You absolutely have to cheat in CAD sometimes. I have occasion to design structures that have diagonal cross bracing that is secured with bolts at each end. There is absolutely no way that concentric mates will work at both ends of the brace. I'll use a concentric mate at one end and if the holes are very, very close, a tangent mate at the other. If they are too far apart and the holes in the brace are on its centerline, I'll use a 'width' mate (in Solidworks) that acts like a pin in a slot.Why cheat in CAD? We can draw things bang on. I get that the manufacturing process requires tolerances but the CAD itself doesn't need that.
But tell us more about the "width" mate, that is relevant here. I do not recall that from using Solidworks.
Am I missing soemthing here? Why not just draw it correctly?You absolutely have to cheat in CAD sometimes. I have occasion to design structures that have diagonal cross bracing that is secured with bolts at each end. There is absolutely no way that concentric mates will work at both ends of the brace. I'll use a concentric mate at one end and if the holes are very, very close, a tangent mate at the other. If they are too far apart and the holes in the brace are on its centerline, I'll use a 'width' mate (in Solidworks) that acts like a pin in a slot.
+1000 for this!Width Mates
A width mate constrains a tab between two planar faces.
Width references can include:
Tab references can include:
- Two parallel planar faces
- Two non-parallel planar faces (with or without draft)
Examples:
- Two parallel planar faces
- Two non-parallel planar faces (with or without draft)
- One cylindrical face or axis
To add a width mate:
- Click Mate
(Assembly toolbar) or Insert > Mate.- Under Advanced Mates, click Width
.- Under Mate Selections:
- Select two planar faces for Width selections.
- Select two planar faces, or one cylindrical face or axis, for Tab selections.
- Under Advanced Mates, select one of the following constraints:
Option Description
Centered Centers a tab within the width of a groove.
Free Lets the components move freely within the limits of the selected faces or planes with respect to the components.
Dimension Sets a distance or angle dimension from one selection set to the closest opposing selection set of faces or planes.
Percent Sets the distance or angle based on a percentage value dimension from one set of the selection set to the center of the other selection set.- Click
.
The components align so that the tab is mated between the faces of the groove. The tab can translate along the center plane of the groove and rotate about an axis normal to the center plane. The width mate prevents the tab from translating or rotating side to side.
Am I missing soemthing here? Why not just draw it correctly?
Please let me fix my math error: In the second example the tubes would be 12m and 7.48m. Sheesh!Yes, you are missing something. Imagine two tubes each a little more than 10 meters long with a hole 1 cm from each end - holes are exactly 10 meters apart. Assemble them at right angles by thru bolting. The diagonal brace connecting the free ends will need to have its holes
14.142135623730950488016887242096980785696718753769480731766797379907324784{more...} meters apart or the other tubes will not be held at right angles. If I place the holes at a reasonably accurate 1,414.21 cm, the mate won't work.
If I have another structure with tube lengths of 12m and 18.55m, then the same diagonal tube (which must fit both structures without modification) will fit fine in practice, but the mate will fail even if it _was_ perfect in the first example. This situation occurs pretty frequently for me.
Just tried this and you're right.Yes, you are missing something. Imagine two tubes each a little more than 10 meters long with a hole 1 cm from each end - holes are exactly 10 meters apart. Assemble them at right angles by thru bolting. The diagonal brace connecting the free ends will need to have its holes
14.142135623730950488016887242096980785696718753769480731766797379907324784{more...} meters apart or the other tubes will not be held at right angles. If I place the holes at a reasonably accurate 1,414.21 cm, the mate won't work.
If I have another structure with tube lengths of 12m and 18.55m, then the same diagonal tube (which must fit both structures without modification) will fit fine in practice, but the mate will fail even if it _was_ perfect in the first example. This situation occurs pretty frequently for me.
Please let me fix my math error: In the second example the tubes would be 12m and 7.48m. Sheesh!
iirc it's 19 places. But you're right, this is a problem. Not something that comes up in my work so I don't pick up on it. And of course there are ways aroind it but a new constraint for this couldn't hurt.I am told that Alibre actually uses something like 12 or 14 places internally,
Yes, you are missing something. Imagine two tubes each a little more than 10 meters long with a hole 1 cm from each end - holes are exactly 10 meters apart. Assemble them at right angles by thru bolting. The diagonal brace connecting the free ends will need to have its holes
14.142135623730950488016887242096980785696718753769480731766797379907324784{more...} meters apart or the other tubes will not be held at right angles. If I place the holes at a reasonably accurate 1,414.21 cm, the mate won't work.
If I have another structure with tube lengths of 12m and 18.55m, then the same diagonal tube (which must fit both structures without modification) will fit fine in practice, but the mate will fail even if it _was_ perfect in the first example. This situation occurs pretty frequently for me.
iirc it's 19 places. But you're right, this is a problem. Not something that comes up in my work so I don't pick up on it. And of course there are ways aroind it but a new constraint for this couldn't hurt.