Drawing a cam lobe profile

Is there a technique for drawing a cam lobe profile onto a circle. I’m trying to replicate a part for a sewing machine. It has a cam lobe shape although it doesn’t actually function as a cam.

I have drawn the major parts in the following skip but I’d like a cam lobe profile for the top. The arc tools don’t seem to do it for me. Is there another way>
Kenmore set ring.skp (113.4 KB)

Something along these lines perhaps.
GIF 12-01-2024 9-37-06 AM


Thanks Box. That’s what I’m trying to do. Interesting to see you were able to accomplish with it the basic tools. I’ll be reviewing this several times to learn how you did it.

Do you know if there’s a way for me to to step through it? Every time I pause it, it ends up going back to the start instead of continuing on from the pause. I’m just trying to figure out all of your tool selections and how you position them.

Thank you very much.

I recorded another version which you should be able to pause.
But it is really just the line tool and the 2 point arc. The ‘mirror’ is just copy/rotate.
This time I made the edge tangent to the circle. You can play around with it to get the exact shape you want, you could even use the image to trace it.


Thanks again Box. I’m often guilty of thinking there’s some magic tool out there to solve my problem. You have shown me that mastery of basic tools is sufficient to solve this particular problem. I know I’ll be looking into that mirroring operation, where you copied the left side over to the right. I’ve seen that done before but I haven’t got comfortable with it yet.

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It is really very simple, you simply click and drag the rotate tool to set the axis of rotation, then rotate a copy 180deg.

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Box, I’ve used your techniques to draw the shape I want. But I’ve ended up with an open bottom. Solid Inspector shows a lot of red but do you have any suggestions on how to go about making this solid,(or how to avoid ending up with open surfaces).
Kenmore set ring open bottom.skp (167.4 KB)

I drew it again and checking each step along the way I ended up with a solid object.
Kenmore set ring solid.skp (93.1 KB)

This is normal behavour for PushPull if you are pulling a face that is attached to another face.
I don’t see an attached face in your drawing but you could have erased some edges after the PushPull…
If you ensure it is 1 face before you Pull it should have a bottom!

Thanks for the tip. I’ll try to keep it in mind.

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You didn’t need to redraw it, just tracing an edge will form a face if it is flat, and another edge just to break the inner ring, delete and it is solid.
GIF 13-01-2024 11-50-12 AM

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For some reason, I was drawing lines from one edge to the other edge, not tracing a portion of an edge. My technique didn’t work but yours did!

Thanks again.

Edge to edge should work too, perhaps you didn’t have the component open for editing when you tried that.

Edit: Actually you are correct, edge to edge doesn’t work in this case, there must be something slightly odd with the geometry.

That is something I can’t say I have noticed before, when there is a hole in the face you need to go all the way across for it to work. I guess I never noticed because I usually trace an edge.
GIF 13-01-2024 2-05-50 PM

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Alternatively you can draw two edges between inside and outside.

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That’s what I was trying to do, but I must have messed up some of my geometry so that it didn’t work.

Tried it again, and it worked this time, so I must not have been careful enough in drawing my lines.

In this particular case, if the two faces are to be parallel, you can also use the technique shown in this SU file.

Closing an annular face.skp (266.2 KB)

Thanks for another option to solve this.

It took a few tries but I think I finally got something that will be useful. I learned a lot getting to this point and I have to thank this forum for being so helpful.