Cam path issues

Hello there. I am a high school student whose experience with CAD in general was limited before I got into Rhino, but I am impressed by how easy to use and learn this software is. I’ve been messing around with it for about six months and am ready to partake in my first ‘serious’ project using it, however, I have hit a quite large dead end.
You see, I do not know how to create a cam path for a cam pin on this device I am designing. As shown in the picture attached, I have where the pin starts, where it first begins to rise, and where it should end; the end result of this should be that the outer piece is pulled back via merely the upward movement of the cam pin.
I do not know how to create the path of the cam pin in a simple and straightforward way, and have been spending the last few hours quite boggled. Any help is dearly appreciated.

Hello - can you post what you have? I guess the path is more or less ‘s’ shaped, correct?


‘up-pull’.3dm (272.4 KB)
More like a straight line, although it’s through a curved surface. In the file I added I put a black line visible on the front layer showing what I mean.

Hello - here’s what I’d do I think to get the ramp shape:

  • Make copies of the cylinders (ExtractSrf>Copy=Yes) at each end of the travel and Untrim those
  • Make a copy of the outer surface of the thickened cylinder that gets the cut and UntrimAll
  • Set point on that surface at the center of the cylinders.
  • ShortPath on the surface between the two points,
  • Fin (Extrude curve normal) the short path inward
  • OffsetSrf, BothSides, Solid=No the fin surface - these will be the walls of the ramp.
  • Clean up =)

@redmccloud - is this on the right track?

'up-pull _Maybe.3dm (65.8 KB)


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I unfortunately have little to no idea of how the commands you have mentioned work (sorry, I am still extremely new to the program, even if I like to pretend otherwise, heh). But I did make copies of the cylinders at the end of travel for both ends, untrimmed them, and have made a copy of the outer cylinder and UntrimAll’d it. I do not know how to set a point on the surface at the center of the cylinders, however.

To the edit: I have no clue how you managed to make this sir, but this is precisely what I am attempting to do, except I am also trying to create a small path between the ‘safety slot’ and then the beginning of this path. I still have a lot to learn, I see.

@redmccloud - here is a little clip with the basics of what I did there:


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Oh wow, this is above and beyond what I was expecting for help! This is extremely clear and well-documented, I think I can understand what to do now. Thank you so much Mr. Golay, you are a life-saver for this project of mine!

Once again, this issue has reared its ugly head once more.
I have been using this method shown in the attached video to great effect, however, when I try it this time, on this specific piece, it doesn’t work at all.

You see, what I am attempting now is to create a very small, very slight cam path, for a pin attached to a central axle that rotates ever so slightly as the central carrier piece moves back and forth, to lock and unlock.

However, even with the instructions provided, all I end up with is this ugly mess instead of a smooth path:

I’ve redone this at least four times now, and this is the best try I have gotten so far. Any feedback and advice on this conundrum would be appreciated, as I still have no idea what to do here and why the previously portrayed techniques didn’t work.
try and try again.3dm (329.3 KB)

Hello - is this the result you’re after?

try and try again_Again.3dm (214.0 KB)

Same idea as before - the cyan curve is the ‘short path’


Mr. Golay, you are a miracle worker. Still, if it’s the same idea as before, I have no clue how I kept ending up at the weird, jagged shape that I kept creating. What you’ve made is extremely smooth and perfectly contoured… I really do suck at this stuff, heh.

Hello - No you don’t suck at it, you just need to mess with it a bit more and think with how the program works and surfacing works, which is not necessarily always obvious. I’ll try to lay out the steps I used in the next day or two in an understandable way and maybe that will be enough to go on, but, basically:

1.Make the cylinders complete and extended well past the eventual inner and outer boundary surfaces (cylinder and plane)
2. ShortPath between the centers of the end cylinders as pulled to the inner horizontal cylinder.
3. OffsetSrf to both sides.
4. ExtendSrf the offsets to pass through the inner and outer boundaries.
5. Ideally the surfaces are already tangent to the small angled cylinders but I used MatchSrf to be sure.
6. Trim all of these back to the inner cylinder and outer plane
7. Trim the shortened cylinders with the edges of the offsets - i.e. get rid of the part of the cylinders that goes into the slot and only keep the 180 degrees or so on each end.
8. Trim the inner cylinder and outer plane with the combined edges of the cylinder halves and the walls of the slot.


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