trying to model the ball path for a ball screw

david_lang457

This is a helix where at the end of the helix, there is a tunnel through the body to the other end of the helix. I'm stuck on how to join the ends of the helix, directing the path into the cylinder, then towards the other end of the helix, then back out of the cylinder (all of these through a reasonably gradual curve that the balls have a chance of following

david_lang457

https://cad.onshape.com/documents/f6216bcdc4729fc4af71800f/w/541cac61998a304cd54cf736/e/b0afb2d01ea052af523b128a has a simple cylinder with helix that I'm trying to join

robert_scott_jr_

Hello David. Being a novice, I played around with your document for some time before I could get the sweep to complete end to end. The helix and top 3d fit spline you had created worked ok but I could not get it to complete through the rest of the paths.

I had discovered that the end of the helix bottom end and the end of the next sketch path were in the same plane so I thought I could simply use an arc on a plane I created at one of those two points and parallel to the top plane. The attempt at a sweep failed; I could see that the end of the sweep that would fail to continue to the next path was not perpendicular to the previous path. Using another 3d fit spline in lieu of the arc and putting the sweep profile on a plane using a vertex from sketch 2 and parallel to the right plane got it to work.

https://cad.onshape.com/documents/a877c48d8f7c3008b13a9ad0/w/c8ea01de50575ffc37a3485a/e/4dab626a688d23dd810fb016

david_lang457

so limiting the use of 3d fit splines to operating only on a single plane seems to be the key (although even there, trying to control the amount of curve seems to be non-trivial

John_P_Desilets

@david_lang457 Check out this example. I used projected curves instead of 3D splines. 

https://cad.onshape.com/documents/c1d5dc8c56f732551ddcaefb/w/a415d2db956703919a70eff5/e/d4a34f74ce96c65187dac2cb

david_lang457

I tried projected curves but couldn't get it to work. I guess I didn't have sufficient overlap or something. That would give me the full control I'm looking for.

david_lang457

projected curves was the answer. It seems very picky about what two views you use to form the curve, but I was finally able to get it worked out