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help how to make this part?


Please help

i need to make a part which is a cylinder but with a special cam grove on it. i tried a VSS with a datam graph, but it doesnt work with a 90deg rise in the graph.

anyone know how i can do this?

the cam entrance and exits must be parallel to eachother, and be centered off the axis of rotation. The grove continues from the entrance along the center of the cam until it meets up with the exit part of the vss.

The idea of this cam is convert continuious rotation in the X direction to segmented rotation in the y direction.

View attachment 133

View attachment 134

anyone have any ideaS? sugestions? tutorials ? similar parts? or even know what this form of power transfer is called?


New member
I'm not getting what your part should look like, but maybe this will be useful....

For a groove cut on a cylinder (end mill cut, cutter axis intersects cylinder axis at right angle) I usually create a surface which will represent the cutter axis path and offset that cutter radius in each direction to create the groove sides.

You can wrap a planar curve to the cylinder then project that normal to surface to a smaller cylinder. Blend between the two curves to create the mid surf. (I think it might be best to use over and under sized cylinders so you will have some to trim away for the final surfs and use approximate composite curves for the blend). What you'll want out of the mid surf; if you run a line from any point on the outer edge to intersect the axis of the cylinder, that line should lie on the surface.

Don't know if that's the easiest or cleanest way, but it should give a good rep of the cut groove.


New member
You might try to model one side of the cam profile first then do the other.

It is a little difficult to visualize the problem. If the cam position on the side of the cylinder changes you might try wrapping a datum curve on the cylinder and then sweeping a protrusion/cut along this trajectory.

Do you have the picture of the physical part you can post?


New member
Something like this?

View attachment 393

First part of the curve from equation:




The middle section is sketched, the end transformed.

The second corve is the same, with r=4

VSS the circle along the two curves.

Hope this helps!



New member

Excellent job! I would really like to examine in more detail exactly how you did this.

I'm with puppet - would you mind uploading for all on the forum? If not, please consider emailing it to me:

[email protected]




New member
And here is the file!


In 2001, for your convenience.

(I installed wildfire and tried it, but have not started any projects with it!)

Challenge me with more complex (surfacing) parts!



hey dude. try as i might. i can not find tutoirals or explinations as to how u came up with the equations to drive the geometry.

any chance u can help me out and explain it? or point me to the right place were i can find examples?



Im not sure how the cam profile should work but here is another way, simpler, that may also work. I used a formed curve, used a 90 sector of a circle a horizontal line and another 90 sector. I sletched it and added a relation to make the overall dimensiom, end to end, equal to the circumference of the cylinder. Then a simple sweep to create the cut.

View attachment 394

and a section to match yours.

View attachment 395


Thanks kvision Your reply was the most helpful.

I appreciate the 1st reply but its much to complex for me. I think i need to learn more about using equations to drive geometry.

Anyone know of any good tutorials?

thanks to all that helped

Da- PuPpEt