1071 lines
49 KiB
Plaintext
1071 lines
49 KiB
Plaintext
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This is a reference manual for MechSketch. This document is not intended
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for new users; to learn about this program, see the video tutorials.
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<h2>General Navigation</h2>
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Two windows appear on the screen: a larger window that contains
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graphics, and a smaller window that contains text. The graphics
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window is used to draw the geometry, and to view the 3d model. The
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text window provides information about the model, and may also be
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used to modify settings and numerical parameters.
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<h3>Graphics Window and Model View</h3>
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To pan the view, right-drag with the mouse.
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To rotate the view, center-drag with the mouse. This turns the
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part over, so that the surfaces that used to be hidden (because
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they were facing backwards, away from the viewer) become visible.
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To rotate the view within the plane of the monitor,
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Ctrl+center-drag with the mouse.
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It is also possible to pan by Shift+center-dragging, or to rotate
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by Shift+right-dragging.
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To zoom in or out, rotate the scroll wheel. It is also possible to
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zoom by using the View menu, or the associated keyboard shortcuts
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(+ and -).
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To zoom to the extent of the part, choose View -> Zoom To
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Fit. This adjusts the zoom level so that the part fits exactly
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on the screen, and then pans to center the part. The rotation
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of the part is not affected.
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If a workplane is active, then choose Sketch -> In Workplane (or
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press W) to align the view to the workplane. After doing this,
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the plane of the screen is coincident with the workplane.
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The x, y, and z coordinate axes are always drawn at the bottom
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left of the graphics window, in red, green, and blue. These axes
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are live. They can be highlighted and selected with the mouse, in
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the same way as any other normals. (This means that the coordinate
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axes are always conveniently available on-screen, which is useful
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e.g. when constraining a line parallel to the x-axis.)
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<h3>Dimension Entry and Units</h3>
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Dimensions may be displayed in either millimeters or inches.
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Millimeter dimensions are always displayed with two digits
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after the decimal point (45.23), and inch dimensions are always
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displayed with three (1.781).
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Choose View -> Dimensions in ... to change the current display
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units. This does not change the model; if the user changes from
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inches to millimeters, then a dimension that was entered as 1.0
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is now displayed as 25.40.
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All dimensions are entered in the current display units. In most
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places where a dimension is expected, it's possible to enter an
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arithmetic expression ("4*20 + 7") instead of a single number.
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<h3>Text Window</h3>
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The text window appears as a floating palette window. It may
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be shown or hidden by pressing Tab, or by choosing View ->
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Show Text Window.
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The text window works like a web browser. Any underlined text
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is a link. To activate a link, click it with the mouse. The links
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may be used to navigate to other pages in the text window. For
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example, the "home" screen is a list of groups in the sketch:
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<img src="/pics/ref-text-window.png" />
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To navigate to a group's page, click on that group's name (e.g.,
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"g002-sketch-in-plane". The links may also taken actions in the
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sketch. For example, in the above screenshot, all of the groups
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are shown. To hide a group, click on the word "yes" in the
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"show" column.
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As a convenience, the text window will sometimes automatically
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navigate to a page that is likely to be relevant. For example,
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when a new group is created, the text window displays that new
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group's page. It's always possible to navigate to a different
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page, by clicking the "home" link at the top left corner (or
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pressing Esc), and following the links from there.
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<h3>Show / Hide Entities</h3>
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As the sketch becomes more complex, it may be useful to hide
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unnecessary information. MechSketch provides several different
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ways to do this.
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In the second and third line of the text window, links are
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provided to hide and show different things. These are:
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wrkpls -- When a new "Sketch In New Workplane" group is
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created, an associated workplane is created
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automatically. If wrkpls is hidden, then that
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workplane is visible only when its associated
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group is active. If wrkpls is shown, then the
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workplane is always visible.
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normals -- By default, normals are drawn as blue-grey arrows,
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in the direction of the normal. These normals may
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be hovered and selected with the mouse, for
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example in order to constrain them. This link
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may be used to hide them.
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points -- By default, points are drawn as green squares.
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These points may be hovered and selected with the
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mouse, for example in order to constrain them.
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This link may be used to hide them. If points are
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hidden, then they will still appear when the mouse
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hovers over them, and may still be selected.
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constraints - When a constraint is created, a graphical
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representation of that constraint is displayed
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in purple. The constraints in a group are
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visible only when that group is active. To hide
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them even then, use this link.
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shaded -- The 3d part is displayed as an opaque solid,
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with lighting effects to give the impression of
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depth. This link may be used to hide that
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view.
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faces -- Some surfaces on the 3d model may be selected.
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For example, the user can select a plane face
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of the part, and constrain a point to lie on
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that plane. If faces are shown, then the faces
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will appear highlighted when the mouse hovers
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over them. The user can click the mouse to
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select the face, as they would for any other
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entity.
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As a convenience, faces are automatically
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hidden when a new sketch group is created,
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and automatically shown when a new extrusion is
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created. If this behavior is not what's desired,
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then the faces can be shown or hidden manually
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with this link.
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mesh -- The 3d model of the part consists of many
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triangles; for example, a flat polygon with
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n sides is broken down into n - 2 triangles.
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Use this link to show the triangles on the
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model. In general, this is useful only for
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debugging, or to see how fine the mesh is
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before exporting it.
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hidden-lines - With the part in a given orientation, some of
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the lines in the part will be invisible,
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because they are buried inside the solid part.
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To show those lines anyways, as if the part
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were transparent, use this link. This may be
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useful when drawing a sketch that lies within
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the volume of the part.
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In addition to the above options, it is possible to hide and show
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entire groups. If a group is hidden, then all of the entities
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(line segments, circles, arcs, points, etc.) from that group
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are hidden.
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To hide a group, go to the home screen in the text window, by
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pressing Esc or choosing the link at the top left. A list of
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groups is displayed, along with their visibility. If a group is
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visible, then the "show" column contains the word "yes" in green.
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Click the "yes"; it now appears as a greyed "no", and the group
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is hidden.
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The show / hide status of groups is saved in the part file. If
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a part is imported into an assembly, then entities that were
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visible in the part file will be visible in the assembly, and
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entities that were hidden will be hidden.
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<h3>Active Workplane</h3>
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MechSketch represents all geometry in 3d; it's possible to draw
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line segments anywhere, not just in some plane.
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This freedom is not always useful, so MechSketch also makes
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it possible to draw in a plane. If a workplane is active, then
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all entities that are drawn will be forced to lie that plane.
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The active workplane ("wrkpl") is indicated in the top line of
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the text window, at the right.
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When MechSketch starts with a new empty file, a workplane parallel
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to the XY plane is active. To deactivate the workplane, and draw
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in 3d, choose Sketch -> Anywhere In 3d.
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To activate a workplane, select it, and then choose Sketch ->
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In Workplane. When a workplane is activated, the view is aligned
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onto that workplane. (The workplane remains active until the
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user chooses Sketch -> Anywhere In 3d, or a different workplane
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is activated. If the user rotates the view, so that the view
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is no longer aligned onto the workplane, then the workplane
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remains active.)
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In a "Sketch in New Workplane" group, the group's associated
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workplane may be activated by choosing Sketch -> In Workplane;
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there is no need to select it first.
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<h3>Active Group</h3>
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When a new line, circle, or other curve is created, it will be
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created in the active group.
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Geometry from the active group is drawn in white; geometry from
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earlier groups is drawn in brown. Later groups are hidden.
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In the text window's home screen (press Escape, or choose the
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link in the top left corner), the active group's line in the
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list of groups has "yes" in the "actv" column. All other groups
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(except g001-#references, which cannot be activated) have "no"
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in that column. To activate an inactive group, click on the "no".
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<h2>Sketch Entities</h2>
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<h3>Construction Geometry</h3>
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In normal operation, the user draws line and curves in a
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sketch. Those curves describe the geometry to be manufactured;
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ultimately, the endmill or the laser or some other tool will
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cut along those curves.
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In some cases, it is useful to draw a line that should not appear
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on the final part. For example, the user may wish to draw a center
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line for a symmetric part; but that center line only exists as
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a guide, and should not actually get exported with the CAM data.
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Or the user may wish to draw the axis of revolution for a lathe
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group. These lines are called construction lines.
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To mark an entity as construction-only, choose Sketch -> Toggle
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Construction. A construction entity will behave just like any
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other entity, except that it is drawn in green, and does not
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contribute to the geometry for export (or for extrusion or
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lathing or sweeping).
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<h3>Datum Point</h3>
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This entity is defined by a single point.
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If a workplane is active when the datum point is created,
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then that datum point will always lie in the workplane. If no
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workplane is active, then the datum point will be free in 3d.
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(This is the same behaviour as for all points, including e.g. the
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endpoints of a line segment.)
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Datum points are typically used as construction geometry. The user
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might place datum points in order to simplify the dimensioning
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of line segments or other entities.
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<h3>Workplane</h3>
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This entity is specified by a point and a normal. The point
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defines its origin, and the normal defines its orientation.
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A workplane makes it possible to draw a section in 2d. If a
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workplane is active, then any entities that are drawn must lie
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in that workplane.
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It's almost never necessary to create workplanes explicitly.
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Instead, create a new Sketch in New Workplane group.
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<h3>Line Segment</h3>
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This entity is specified by its two endpoints. If a workplane is
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active, then the two endpoints will always lie in that workplane.
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To create the line segment, choose Sketch -> Line Segment, and
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then left-click one endpoint of the line. Then release the mouse
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button; the other endpoint is now being dragged.
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To create another line segment, that shares an endpoint with
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the line segment that was just created, left-click again. This
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is a fast way to draw closed polygons.
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To stop drawing line segments, press Escape, or right- or
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center-click the mouse. MechSketch will also stop drawing new
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line segments if an automatic constraint is inserted. (For
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example, draw a closed polygon by left-clicking continuously, and
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then hovering over the starting point before left-clicking the
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last time. The endpoint of the polyline will be constrained to
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lie on the starting point, and since a constraint was inserted,
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MechSketch will stop drawing.)
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<h3>Rectangle</h3>
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A rectangle consists of two vertical line segments, and two
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horizontal line segments, arranged to form a closed curve.
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Initially, the rectangle is specified with the mouse by two
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diagonally opposite corners. The line segments (and points)
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in the rectangle may be constrained in the same way as ordinary
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line segments.
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It would be possible to draw the same figure by hand, by drawing
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four line segments and inserting the appropriate constraints. The
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rectangle command is a faster way to draw the exact same thing.
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A workplane must be active when the rectangle is drawn, since
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the workplane defines the meaning of "horizontal" and "vertical".
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<h3>Circle</h3>
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This entity is specified by its center point, by its diameter,
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and by its normal.
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To create the circle, choose Sketch -> Circle, and then left-click
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the center. Then release the mouse button; the diameter of
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the circle is now being dragged. Left-click again to place
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the diameter.
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If a workplane is active, then the center point must lie in
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that workplane, and the circle's normal is parallel to the
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workplane's normal (which means that the circle lies in the
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plane of the workplane).
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If no workplane is active, then the center point is free in space,
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and the normal may be dragged (or constrained) to determine the
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circle's orientation.
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<h3>Arc of a Circle</h3>
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This entity is specified by its center point, the two endpoints,
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and its normal.
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To create the arc, choose Sketch -> Arc of a Circle, and then
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left-click one of its endpoints. Then release the mouse button;
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the other endpoint is now being dragged. The center is also being
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dragged, in such a way as to form an exact semi-circle.
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Left-click again to place the other endpoint, and then drag the
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center to the desired position. The arc is drawn counter-clockwise
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from the first point to the second.
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The arc must be drawn in a workplane; it cannot be drawn in
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free space.
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Tangent arcs may be created automatically. To do so, first select
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a point where two line segments join. Then choose Sketch ->
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Arc of a Circle; the arc will be created, and automatically
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constrained tangent to the two line segments.
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The initial line segments will become construction lines, and
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two new lines will be created, that join up to the arc.
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The arc's diameter may then be constrained in the usual way, with
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Distance / Diameter or Equal Length / Radius constraints. This
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is a simple way to round a sharp corner.
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<h3>Bezier Cubic Segment</h3>
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This entity is specified by its four Bezier points: two endpoints,
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and two (in general, off-curve) control points.
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To create the Bezier cubic, choose Sketch -> Bezier Cubic
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Segment. Then left-click one endpoint of the cubic segment.
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Release the mouse button; the other endpoint of the cubic segment
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is now being dragged.
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The two control points are intially placed on the straight line
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between the endpoints; this means that the cubic originally
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appears as a straight line. Drag the control points to produce
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the desired curve.
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<h3>Text in a TrueType Font</h3>
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This entity is defined by two points, at the top left and bottom
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left of the text. The distance between the points determines the
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height of the text; the angle of the line between them determines
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the orientation of the text, and their position determines the
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text's position.
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To create the text, choose Sketch -> Text in TrueType Font. Then
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left-click the top left point of the text. The bottom right point
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of the text is now being dragged; left-click again to place it.
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To change the font, select the text entity. A list of installed
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fonts appears in the text window; click the font name to select
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it. To change the displayed text, select the text entity and
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click the [change] link in the text window.
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<h2>Constraints</h2>
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<h3>General</h3>
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To create a constraint, first select the geometry to be
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constrained. For example, when constraining the distance between
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two points, first select those two points. Then choose the
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appropriate constraint from the Constrain menu.
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Depending on what is selected, the same menu item may generate
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different constraints. For example, the Distance / Diameter menu
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item will generate a diameter constraint if a circle is selected,
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but a length constraint if a line segment is selected. If the
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selected items do not correspond to an available constraint,
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then MechSketch will display an error message, and a list of
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available constraints.
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Constraints are drawn in purple on the sketch. If a constraint
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has a label associated with it (e.g. a distance or an angle),
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then that label may be repositioned by dragging it with the
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mouse. To modify the dimension, double-click the label; a text
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box will appear on the screen, where the new dimension can be
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entered. Then press enter.
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<h3>Reference Dimensions</h3>
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By default, the dimension drives the geometry. If a line segment
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is constrained to have a length of 20.00 mm, then the line
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segment is modified until that length is accurate.
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A reference dimension is the reverse: the geometry drives the
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dimension. If a line segment has a reference dimension on its
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length, then it's still possible to freely change that length,
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and the dimension displays whatever that length happens to be. A
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reference dimension does not constrain the geometry.
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To change a dimension into a reference dimension, choose Constrain
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-> Toggle Reference Dimension. A reference dimension is drawn with
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"REF" appended to the displayed length or angle. Double-clicking
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a reference dimension does nothing; the dimension is specified
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by the geometry, not the user, so it is not meaningful to type
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in a new value for the reference dimension.
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<h3>Distance / Diameter</h3>
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This constraint sets the diameter of an arc or a circle, or the
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length of a line segment, or the distance between a point and
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some other entity.
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<h3>Angle</h3>
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When two lines intersect, four angles are formed. These angles
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form two equal pairs. For example, the pictured lines interesect
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at 30 degrees and 150 degrees. These two angles (30 and 150) are
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known as supplementary angles, and they always sum to 180 degrees.
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<img src="/pics/tut-line-cross-angles.png" />
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(Notice that in the sketch, three of the angle constraints are
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reference dimensions. Given any one of the angles, we could
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calculate the other three; so a sketch that specified more than
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one of those angles would be overconstrained, and fail to solve.)
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When a new angle constraint is created, MechSketch chooses
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arbitrarily which supplementary angle to constrain. An arc is
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drawn on the sketch, to indicate which angle was chosen. As the
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constraint label is dragged, the arc will follow.
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If the wrong supplementary angle is constrained, then select the
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constraint and choose Constrain -> Other Supplementary Angle. A
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constraint of 30 degrees on one supplementary angle is exactly
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equivalent to a constraint of 150 degrees on the other.
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<h3>Horizontal / Vertical</h3>
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This constraint forces a line segment to be horizontal or
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vertical. It may also be applied to two points, in which case
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it applies to the line segment connecting those points.
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A workplane must be active, because the meaning of "horizontal"
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or "vertical" is defined by the workplane.
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It's good to use horizontal and vertical constraints whenever
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possible. These constraints are very simple to solve, and will
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not lead to convergence problems. Whenever possible, define
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the workplanes so that lines are horizontal and vertical within
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those workplanes.
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<h3>On Point / Curve / Plane</h3>
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<h3>Equal Length / Radius</h3>
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<h3>Length Ratio</h3>
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<h3>At Midpoint</h3>
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<h3>Symmetric</h3>
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This constraint forces two points to be symmetric about some
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plane. Conceptually, this means that if we placed a mirror at
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the symmetry plane, and looked at the reflection of point A,
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then it would appear to lie on top of point B.
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The symmetry plane may be specified explicitly, by selecting a
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workplane. Or, the symmetry plane may be specified as a line in
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a workplane; the symmetry plane is then through that line, and
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normal to the workplane. Or, the symmetry plane may be omitted;
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|
in that case, it is inferred to be either parallel to the active
|
|
workplane's vertical axis or its horizontal axis. The horizontal
|
|
or vertical axis is chosen, depending which is closer to the
|
|
configuration in which the points were initially drawn.
|
|
|
|
<h3>Parallel / Tangent</h3>
|
|
|
|
In 2d (i.e., when a workplane is active), a zero-degree angle
|
|
constraint is equivalent to a parallel constraint. In 3d, it
|
|
is not.
|
|
|
|
Given a unit vector A, and some angle theta, there are in general
|
|
infinitely many unit vectors that make an angle theta with A. (For
|
|
example, if we are given the vector (1, 0, 0), then (0, 1, 0),
|
|
(0, 0, 1), and many other unit vectors all make a ninety-degree
|
|
angle with A.) But this is not true for theta = 0; in that case,
|
|
there are only two, A and -A.
|
|
|
|
This means that while a normal 3d angle constraint will restrict
|
|
only one degree of freedom, a 3d parallel constraint restricts
|
|
two degrees of freedom.
|
|
|
|
<h3>Same Orientation</h3>
|
|
|
|
A normal has a direction; it is drawn as an arrow in that
|
|
direction. The direction of that arrow could be specified by
|
|
two angles. The normal specifies those two angles, plus one
|
|
additional angle that corresponds to the twist about that arrow.
|
|
|
|
(Technically, a normal represents a rotation matrix from one
|
|
coordinate system to another. It is represented internally as
|
|
a unit quaternion.)
|
|
|
|
For example, the picture below shows two workplanes, whose
|
|
normals are constrained to be parallel:
|
|
|
|
<img src="/pics/tut-parallel-normals.png" />
|
|
|
|
Because the normals are parallel, the planes are parallel. But one
|
|
plane is twisted with respect to the other, so the planes are not
|
|
identical. The line on the left is constrained to be horizontal
|
|
in the leftmost plane, and the line on the right is constrained
|
|
to be horizontal in the rightmost. These lines are not parallel,
|
|
even though the normals of the workplanes are parallel.
|
|
|
|
If we replace the "parallel" constraint with a "same orientation"
|
|
constraint, then the two workplanes become identical, and the
|
|
two horizontal lines become parallel.
|
|
|
|
This is a useful constraint when building an assemblies; a single
|
|
"same orientation" constraint will fix all three of the imported
|
|
part's rotational degrees of freedom.
|
|
|
|
<h3>Comment</h3>
|
|
|
|
A comment is a single line of text that appears on the drawing.
|
|
When the comment is created, it appears in the center of the
|
|
screen. To move the comment, drag it with the mouse. To change
|
|
the text, double-click it.
|
|
|
|
The comment has no effect on the geometry; it is only a
|
|
human-readable note.
|
|
|
|
|
|
<h2>Groups</h2>
|
|
|
|
<h3>General</h3>
|
|
|
|
To view a list of groups, go to the home page of the text window.
|
|
This is accessible from the link at the top left of the text
|
|
window, or by pressing Esc. To view a group's page, click on
|
|
its name in the list.
|
|
|
|
All groups have a name. When the group is created, a default name
|
|
(e.g., "g008-extrude") is assigned. The user may change this name;
|
|
to do so, go to the group's page in the text window, and choose
|
|
[rename].
|
|
|
|
Groups that create a solid (e.g. extrudes or sweeps) have a "MERGE
|
|
AS" option, which is displayed in the page in the text window.
|
|
The group can be merged as union, which adds material to the
|
|
model, or as difference, which cuts material away.
|
|
|
|
These groups also have a color, which determines the color of
|
|
the surfaces they produce. To change the color, click on one of
|
|
the swatches in the group's page in the text window.
|
|
|
|
The group's page in the text window also includes a list of all
|
|
requests, and of all constraints. To identify a constraint or a
|
|
request, hover the mouse over its name; it will appear highlighted
|
|
in the graphics window. To select it, click on the link in the
|
|
text window. This is equivalent to hovering over and clicking
|
|
the actual object in the graphics window.
|
|
|
|
<h3>Sketch in 3d</h3>
|
|
|
|
This creates a new empty group, in which the user may draw lines,
|
|
circles, arcs, and other curves.
|
|
|
|
<h3>Sketch in New Workplane</h3>
|
|
|
|
This creates a new empty group, similar to a new "Sketch in 3d".
|
|
The difference is that a "Sketch in New Workplane" also creates
|
|
a workplane. The workplane is created based on the entities that
|
|
are selected when the sketch is created.
|
|
|
|
A point and two line segments
|
|
|
|
The new workplane has its origin at the specified point. The
|
|
workplane is parallel to the two lines. If the point and
|
|
two are two edges on a plane face of the part, and a vertex
|
|
on that plane face, then the resulting workplane will be
|
|
coincident with that face (i.e., the user will be drawing
|
|
on that face).
|
|
|
|
A point
|
|
|
|
The new workplane has its origin at the specified point. The
|
|
workplane is orthogonal to the base coordinate system; for
|
|
example, its horizontal and vertical axes might lie in the
|
|
+y and -z directions, or +x and +z, or any other combination.
|
|
|
|
The orientation of the workplane is inferred from the
|
|
position of the view when the workplane is created; the
|
|
view is snapped to the nearest orthographic view, and the
|
|
workplane is aligned to that.
|
|
|
|
If a part consists mostly of ninety degree angles, then this
|
|
is a quick way to create workplanes.
|
|
|
|
The new group's associated workplane is automatically set to be
|
|
the active workplane.
|
|
|
|
<h3>Step Translating</h3>
|
|
|
|
This group takes geometry in the active group, and copies it
|
|
multiple times along a straight line.
|
|
|
|
If a workplane is active when the step translating group is
|
|
created, then the translation vector must lie parallel to that
|
|
workplane. Otherwise, the translation vector may go anywhere in
|
|
free space.
|
|
|
|
The number of copies to create is specified by the user. To
|
|
change this value, click the [change] link in the group's page
|
|
in the text window.
|
|
|
|
The copies may be translated on one side, or on two sides. If
|
|
the copies are translated on one side, then the original will
|
|
appear to the left of (or above, below, etc.) all the copies. If
|
|
the copies are translated on two sides, then the original will
|
|
appear in the center of the copies.
|
|
|
|
The copies may be translated starting from the original,
|
|
or starting from copy #1. If the translation starts from the
|
|
original, then the translation will contain the original. (So a
|
|
1-element step will always produce the input geometry exactly.)
|
|
If the translation starts from copy #1, then the original is
|
|
not included in the output. (So a 1-element step makes a single
|
|
copy of the input geometry, and allows the user to translate it
|
|
anywhere in space.)
|
|
|
|
If the active group is a sketch (sketch in 3d, sketch in new
|
|
workplane), the the sketch is stepped and repeated. In that case
|
|
the user would typically draw a section, step and repeat that
|
|
section, and then extrude the step and repeat.
|
|
|
|
If the active group is a solid (extrude, sweep, lathe), then
|
|
the solid is stepped and repeated. In this case, the user would
|
|
draw a section, extrude the section, and then step and repeat
|
|
the extrusion.
|
|
|
|
In some cases, these two possibilities (extrude the step, vs.
|
|
step the extrusion) are equivalent. If the translation vector
|
|
isn't parallel to the section plane, then only the second option
|
|
will work.
|
|
|
|
<h3>Step Rotating</h3>
|
|
|
|
This group takes the geometry in the active group, and copies
|
|
it mutiple times along a circle.
|
|
|
|
Before creating the group, the user must select its axis of
|
|
rotation. One way to do this is to select a point, plus either
|
|
a line segment or a normal; the axis of rotation goes through
|
|
the point, and is parallel to the line segment or normal.
|
|
|
|
If a workplane is active, then it's also possible to select just
|
|
a point; in that case, the axis of rotation goes through that
|
|
point, and is normal to the workplane.
|
|
|
|
By default, three copies are created. If a different number is
|
|
typed in (to the group's page in the text window, as for Step
|
|
Translating), then the copies will be spaced evenly along a
|
|
complete circle.
|
|
|
|
To place the copies along less than (or more than) a complete
|
|
circle, drag a point on one of the copies with the mouse; all
|
|
of the rest will follow, as the step rotation angle is modified.
|
|
Constraints (for example an angle constraint, or a point-on-lie
|
|
constraint) may be used to specify the angle of rotation exactly.
|
|
|
|
THe step and repeat options (one side / two sides, with original /
|
|
with copy #1) are the same as for step translating groups.
|
|
|
|
<h3>Extrude</h3>
|
|
|
|
Before creating a new extrusion, the active group should contain
|
|
a sketch that consists entirely of closed curves. The extrude
|
|
group takes that flat sketch, and extrudes it to form a solid.
|
|
|
|
The sketch may be extruded on one side, or on two sides. If the
|
|
sketch is extruded on one side, then the new solid is either
|
|
entirely above or entirely below the original sketch. (Drag a
|
|
point on the new surface to determine the extrude direction,
|
|
and also to determine the extrude depth. Once the extrusion
|
|
depth looks approximately correct, it may be specified exactly
|
|
by using constraints. For example, select a line on the side of
|
|
the extrusion, and constrain its length.)
|
|
|
|
If the sketch is extruded on two sides, then the original sketch
|
|
lies at the exact midpoint of the new solid. This means that
|
|
the solid is symmetric about the original sketch plane. Later
|
|
dimensioning often becomes simpler when the part has symmetry,
|
|
so it's useful to extrude on two sides whenever possible.
|
|
|
|
If a workplane is active when the group is created, then the
|
|
extrude path is automatically constrained to be normal to that
|
|
workplane. This means, for example, that a rectangle is extruded
|
|
to form a rectangular prism. The extrusion has one degree of
|
|
freedom, so a single distance constraint will fully constrain it.
|
|
This is usually the desired behaviour.
|
|
|
|
If no workplane is active when the group is created, then the
|
|
extrude path may be in any direction. This means that a rectangle
|
|
could be extruded to form a parallelepiped. The extrusion has
|
|
three degrees of freedom. This is not typically useful.
|
|
|
|
By default, no workplane is active in a new extrude group. This
|
|
means that constraints will apply in 3d; for example, a length
|
|
constraint is a constraint on the actual length, and not on the
|
|
length projected into some plane. This is typically the desired
|
|
behaviour, but it's possible to activate a workplane in the usual
|
|
way (by selecting it, then choosing Sketch -> In Workplane).
|
|
|
|
<h3>Lathe</h3>
|
|
|
|
Before creating a new lathe group, the active group should contain
|
|
a sketch that consists entirely of closed curves. The lathe group
|
|
takes that flat sketch, and sweeps it around a specified axis,
|
|
to form a solid of revolution.
|
|
|
|
To create a lathe group, first select a line segment. Then choose
|
|
New Group -> Lathe. The line segment is the axis of revolution.
|
|
|
|
The section must not intersect itself as it is swept along the
|
|
curve. If the section crosses the axis of rotation, then it is
|
|
certain to intersect itself and fail.
|
|
|
|
<h3>Sweep</h3>
|
|
|
|
<h3>Helical Sweep</h3>
|
|
|
|
This group sweeps a section along a helix. It might be used to
|
|
draw a screw thread, or a coil spring.
|
|
|
|
To create a helical sweep, first draw the section to be swept
|
|
along the helix.
|
|
|
|
<h3>Import / Assemble</h3>
|
|
|
|
In MechSketch, there is no distinction between "part" files and
|
|
"assembly" files; it's always possible to import one file into
|
|
another. An "assembly" is just a part file that imports one or
|
|
more other parts.
|
|
|
|
The imported file is not editable within the assembly. It is
|
|
imported exactly as it appears in the source file, but with an
|
|
arbitrary position and orientation. This means that the imported
|
|
part has six degrees of freedom.
|
|
|
|
To move (translate) the part, click any point on the imported
|
|
part and drag it. To rotate the part, click any point and Shift+
|
|
or Ctrl+drag it. The position and orientation of the part may be
|
|
fixed with constraints, in the same way that any other geometry
|
|
is constrained.
|
|
|
|
The Same Orientation constraint is particularly useful when
|
|
importing parts. This one constraint completely determines the
|
|
imported part's rotation. (Select a normal on the imported part,
|
|
select some other normal to constrain it against, and choose
|
|
Constrain -> Same Orientation).
|
|
|
|
Import groups have a special "MERGE AS" option: in addition
|
|
to the usual "union" and "difference", they have "assemble".
|
|
The "assemble" option is identical to "union", except that
|
|
it displays a warning if the components intersect with each
|
|
other. This is useful when checking to see if the assembled parts
|
|
interfere. If the parts interfere, then a warning is displayed
|
|
underneath the "MERGE AS" line in the group's text window page.
|
|
The interfering surfaces are also highlighted in the graphics
|
|
window, in red with black stripes.
|
|
|
|
When an assembly file is loaded, MechSketch loads all of the
|
|
imported files as well. If the imported files are not available,
|
|
then an error occurs. When transfering an assembly file to another
|
|
computer, it's necessary to transfer all of the imported files
|
|
as well.
|
|
|
|
<h2>Analysis</h2>
|
|
|
|
<h3>Trace Point</h3>
|
|
|
|
MechSketch can draw a "trail" behind a point as it moves. This
|
|
is useful when designing mechanisms. The sketch shown below is
|
|
a four-bar linkage:
|
|
|
|
<img src="/pics/ref-point-traced.png" />
|
|
|
|
As the linkage is worked, the midpoint of the top link moves
|
|
along the cyan curve. This image was produced by drawing the
|
|
linkage, tracing that midpoint, and then dragging the linkage
|
|
through its full range of motion with the mouse.
|
|
|
|
To start tracing, select a point, and choose Analyze -> Trace
|
|
Point. When the point moves, a cyan trail will be drawn behind it.
|
|
|
|
To stop tracing, choose Analyze -> Stop Tracing. A dialog
|
|
will appear, with the option to save the trace as a CSV
|
|
(comma-separated value) file. To save the trace, enter a
|
|
filename. To abandon the trace, choose Cancel or hit Esc.
|
|
|
|
The trace is saved as a text file, with one point per line. Each
|
|
point appears in the format x, y, z, separated by commas. Many
|
|
programs, including spreadsheets like Excel, can read this format.
|
|
The units for the coordinates are determined by the export
|
|
scale factor. (If the export scale factor is 1, then they are
|
|
millimeters, and if it's 25.4, then they're inches.)
|
|
|
|
If the mechanism is worked by dragging it with the mouse, then
|
|
the points in the trace will be unevenly spaced, because the
|
|
motion of the mouse is irregular. A plot of x vs. y (like the
|
|
cyan trace above) is not affected, but a plot of x or y vs. t
|
|
is useless, because the "speed" along the curve is not constant.
|
|
|
|
To avoid this problem, move the point by stepping a dimension,
|
|
rather than by dragging with the mouse. Select the dimension to
|
|
be stepped; this can be any distance or angle. Choose Analyze ->
|
|
Step Dimension. Enter the new final value for that dimension,
|
|
and the number of steps; then click "step dimension now".
|
|
|
|
The dimension will be modified in multiple steps, and solved
|
|
at each intermediate value. For example, consider a dimension
|
|
that is now set to 10 degrees. The user steps this dimension to
|
|
30 degrees, in 10 steps. This means that MechSketch will solve
|
|
at 12 degrees, then 14 degrees, then 16, and so on, until it
|
|
reaches 30 degrees.
|
|
|
|
The position of the traced point will be recorded at each
|
|
intermediate value. When the trace is exported, it represents
|
|
the position of that point, as the dimensioned link rotates with
|
|
constant angular speed.
|
|
|
|
The step dimension feature can also improve convergence. In some
|
|
difficult cases, the solver will fail to find a solution when a
|
|
dimension is changed. If the specified constraints have multiple
|
|
solutions, then the solver may also find an undesired solution. In
|
|
this case, it may be useful to try stepping the dimension to
|
|
its new value, instead of changing it in a single step.
|
|
|
|
|
|
<h2>Export</h2>
|
|
|
|
<h3>Bitmap Image</h3>
|
|
|
|
This option will export a bitmap image of whatever is displayed
|
|
on-screen. It is equivalent to taking a screenshot. This option
|
|
is useful for producing human-readable drawings.
|
|
|
|
Choose File -> Export Image. The file is exported as a PNG,
|
|
which most graphics software can open.
|
|
|
|
<h3>2d Vector (DXF)</h3>
|
|
|
|
This option will generate a 2d vector file that represents a
|
|
specified plane in the part. Most 2d CAM software, including the
|
|
software that ships with laser or waterjet cutters, will accept
|
|
a DXF file.
|
|
|
|
Before exporting a DXF, it is necessary to specify which plane of
|
|
the part should be exported. This may be specified by:
|
|
|
|
a face:
|
|
|
|
Any surfaces coplanar with that plane face will appear in the
|
|
file. The faces must be shown before they can be selected;
|
|
click the link in the third line of the text window.
|
|
|
|
a point, and two lines or vectors:
|
|
|
|
The export plane is through the point, and parallel to
|
|
the two lines or vectors. If the two lines or vectors are
|
|
perpendicular, then they will become the x and y axis in the
|
|
DXF file. Whichever line is more horizontal in the current
|
|
view becomes the x axis, and the other one becomes the y.
|
|
|
|
This means that it's possible to rotate the exported DXF
|
|
through ninety degrees by rotating the view through ninety
|
|
degrees (in the plane of that face). Similarly, by rotating
|
|
the part around to look at the face from behind instead of
|
|
in front, the exported DXF is mirrored.
|
|
|
|
the active workplane
|
|
|
|
If a workplane is active, and nothing is selected when the
|
|
export command is chosen, then MechSketch will export any
|
|
surfaces that are coplanar with the active workplane. The
|
|
workplane's horizontal and vertical axes become the x and
|
|
y axis in the DXF file.
|
|
|
|
The units of the DXF file are determined by the export scale
|
|
factor, which may be specified in the configuration screen.
|
|
|
|
<h3>3d Mesh (STL)</h3>
|
|
|
|
This option will generate a 3d triangle mesh that represents
|
|
the entire part. Most 3d CAM software, including the software
|
|
for most 3d printers, will accept an STL file.
|
|
|
|
The mesh from the active group will be exported; this is the
|
|
same mesh that is displayed on screen. The coordinate system
|
|
for the STL file is the same coordinate system in which the part
|
|
is drawn. To use a different coordinate system (e.g., to rotate
|
|
or translate the part), create an assembly with the part in the
|
|
desired position, and then export an STL file of the assembly.
|
|
|
|
The units of the STL file are determined by the export scale
|
|
factor, which may be specified in the configuration screen.
|
|
|
|
<h2>Configuration</h2>
|
|
|
|
<h3>Material Colors</h3>
|
|
|
|
In the text window screen for certain groups (extrude, lathe,
|
|
sweep), a palette of eight colors is displayed. This palette
|
|
allows the user to choose the color of any surfaces generated
|
|
by that group.
|
|
|
|
These eight colors are specified here, by their components.
|
|
The components go from 0 to 1.0. The color "0, 0, 0" is black,
|
|
and "1, 1, 1" is white. The components are specified in the order
|
|
"red, green, blue".
|
|
|
|
A change to the palette colors does not change the color of any
|
|
existing surfaces in the sketch, even if the color of an existing
|
|
surface no longer appears in the palette.
|
|
|
|
<h3>Light Directions</h3>
|
|
|
|
The 3d part is displayed with simulated lighting, to produce
|
|
the impression of depth. The directions and intensities of these
|
|
lights may be modified according to user preference.
|
|
|
|
The lights do not have a position; they have only a direction,
|
|
as if they were coming from very far away. This direction is
|
|
specified in 3 components, "right, top, front". The light with
|
|
direction "1, 0, 0" is coming from the right of the screen.
|
|
The light with direction "-1, 0, 0" is coming from the left of
|
|
the screen. The light with direction "0, 0, 1" is coming from
|
|
in front of the screen.
|
|
|
|
The intensity must lie between 0 and 1. A light with intensity
|
|
0 has no effect, and 1 is full brightness.
|
|
|
|
Two lights are available. If only one is desired, then the second
|
|
may be disabled by setting its intensity to zero. When the part
|
|
is rotated or translated, the lights do not move.
|
|
|
|
<h3>Chord Tolerance</h3>
|
|
|
|
MechSketch does not represent curved edges or surfaces exactly.
|
|
Any curves are broken down into piecewise linear segments,
|
|
and surfaces are represented as triangles.
|
|
|
|
This introduces some error. The chord tolerance determines how
|
|
much error is introduced; it is the maximum distance between
|
|
the exact curve and the line segments that approximate it. If
|
|
the chord tolerance is decreased, then more line segments will
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be generated, to produce a better approximation.
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The chord tolerance is specified in units of screen pixels. This
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means that when the user zooms in on the model, a better
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approximation is produced.
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The same tolerance is used for the mesh that's displayed on
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screen, and for the mesh that is used to export to a file. It
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may be helpful to use a large chord tolerance (2-5 pixels) while
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|
drawing, for fast response, and then temporarily specify a small
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|
chord tolerance (~0.5 pixels) before exporting an STL or DXF file.
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<h3>Perspective Factor</h3>
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To display a 3d part on-screen, it must be projected into 2d. One
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|
common choice is a parallel projection. In a parallel projection,
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|
any two lines that are parallel in real life are also parallel
|
|
in the drawing. A parallel projection is also known as an
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|
axonometric projection. Isometric and orthographic views are
|
|
examples of parallel projections.
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|
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|
Another way to transform the image into 2d is with a perspective
|
|
projection. In a perspective projection, objects closer to the
|
|
"camera" appear larger than objects that are farther away. This
|
|
means that some lines that are parallel in real life will not be
|
|
parallel in the drawing; they will converge at a vanishing point.
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|
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|
A perspective projection will often look more realistic, and
|
|
gives a better impression of depth. The disadvantage is that
|
|
the perspective distorts the image, and may cause confusion.
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|
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|
By default, MechSketch displays a parallel projection. To display
|
|
a perspective projection, set the perspective factor to something
|
|
other than zero. The distance from the "camera" to the model is
|
|
equal to one thousand pixels divided by the perspective factor.
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|
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|
<h3>Edge Color</h3>
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|
|
|
The surfaces of the 3d part are shaded according to the specified
|
|
lighting. Different faces will catch the light at slightly
|
|
different angles, and will therefore appear slightly brighter
|
|
or darker. This permits the viewer to distinguish the boundary
|
|
between the faces.
|
|
|
|
Depending on the lighting, this may not provided very much
|
|
constrast. To make the edges of the part more visible, it's
|
|
possible to emphasize them with a solid-color line.
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|
|
|
If the edge color is specified as "0,0,0", then no emphasized
|
|
edges will be drawn. If any other color is specified, then the
|
|
edges will be drawn in that color. The edge color is specified
|
|
in the same format as for the material color.
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|
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|
<h3>Export Scale Factor</h3>
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|
|
|
Internally, MechSketch represents lengths in millimeters. Before
|
|
exporting geometry to an STL or DXF file, these lengths are
|
|
divided by the export scale factor. This scale factor determines
|
|
the units for the exported file.
|
|
|
|
If the scale factor is set equal to 1, then exported files are
|
|
in millimeter units. If the scale factor is set equal to 25.4,
|
|
then the exported files are in inch units, since 1 inch = 25.4 mm.
|
|
|
|
MechSketch works in a right-handed coordinate system. If the
|
|
scale factor is negative, then the exported file will appear in
|
|
a left-handed coordinate system (so that a right-handed screw
|
|
thread will become left-handed).
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|
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|
<h2>Licensing</h2>
|
|
|
|
As downloaded, MechSketch does not include a license file. This means
|
|
that it cannot create files with more than seven groups. Larger files
|
|
may be opened, but not modified. This light version of MechSketch
|
|
is intended for evaluation, but non-commercial / personal use is
|
|
also permitted.
|
|
|
|
The licensed version of MechSketch can create files with an unlimited
|
|
number of groups.
|
|
|
|
When a license is purchased, a license file ("mechsketch.license")
|
|
will be sent via email. To activate the license, save this file
|
|
somewhere on your computer. In MechSketch, choose Help -> Load
|
|
License... A file dialog box will appear; select the license file.
|
|
|
|
No license server or dongle is required, and licenses do not expire.
|
|
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