# Thread: How to draw Cam lobe

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CAM DRWG.jpgMr Mather Your drawing looks a heck of a sight better than mine but would like for some one to look at it for me.

i know that i am .01 off in the center but what else

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3. Originally Posted by JD Mather
If we assume all of the arcs are tangent and they stop/start at the angles given - there is one solution. (none of the arc centers are on any of the construction lines, but it is fully defined with the given dimensions)
Sounds right.
Originally Posted by JD Mather
(BTW - solution was found in less than 10 minutes.)
In AutoCAD? Seems like someone guessed you would resort to Inventor. Hopefully, AutoCAD can do it, as well. Please post the DWG and explain. I can see how you can constrain the arcs to be coincident and tangent to each other. How did you determine the exact location of the shaft per the given angles? It looks like these are all interdependent and might require trial and error.

4. Originally Posted by AARi
in microstation....
Are you saying you could not do it in AutoCAD? Where is the center of your shaft? Were you able to locate it per the problem?

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6. Originally Posted by neophoible
Sounds right.
In AutoCAD? Seems like someone guessed you would resort to Inventor. Hopefully, AutoCAD can do it, as well. ..
The solution would be identical in AutoCAD - using parametric geometry constraints.
At some point I will try to get around to producing an AutoCAD solution - it is just much faster for me to work in a modern CAD program.

Here is the AutoCAD r2013 edu solution.
Put the hole for the shaft at the origin (0,0,0) I didn't bother with the trivial.

Cam Solution.dwg

7. Originally Posted by AARi
...seems somthing wrong ...
I don't see the specified angles in your "solutions" that were given in the original problem?

Can you turn off the grid in those programs to make it easier to visualize?

8. Originally Posted by JD Mather
The solution would be identical in AutoCAD - using parametric geometry constraints.
At some point I will try to get around to producing an AutoCAD solution - it is just much faster for me to work in a modern CAD program.
Understood. Working out the solution is not quite identical, though, is it? If I ever get a modern computer, maybe I'll switch to a modern program!

Originally Posted by JD Mather
Here is the AutoCAD r2013 edu solution.
Put the hole for the shaft at the origin (0,0,0) I didn't bother with the trivial.
Thanks, JD. I'll try to take a look when I get a chance to convert it to an earlier DWG format. If by trivial, you mean drawing the shaft hole, agreed. If you mean locating it to begin with, well, that seems to me to be a major part of the prob. In fact, it's crucial, as that is where all of the angles are being measured from, right? It seems to me that there would be no unique solution without it.

9. Originally Posted by neophoible
Understood. Working out the solution is not quite identical, though, is it?
The solution is identical. Working out the solution is almost identical. AutoCAD doesn't automatically add coincident constraint to trimmed entities while Inventor does - cuts down on the amount of work a bit (AutoCAD solution took me 24 minutes, working on a laptop, would have been less on my desktop with dual screen larger monitors).

I'll try to take a look when I get a chance to convert it to an earlier DWG format.
I would have saved down myself, except that parametric constraints are critical to the way I found the solution.

If by trivial, you mean drawing the shaft hole, agreed. If you mean locating it to begin with, well, that seems to me to be a major part of the prob.
Rather obvious that it is a circle at the vertex of the angled lines. (keyway is also trivial)

I applied a Fixed constraint at the vertex (at the origin). If the fixed constraint is removed the entire cam can be dragged around the screen without distortion using any point as it is fully constrained (the position constraint being the only one defined by Fixed).

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