How do I create a sketch or path to machine along that varies in Z?

[hooverwelding]

I would like to make a marble roller of sorts....In the attached file I made a sketch that I would like to machine with a ball end mill to make a trough for a marble to roll in.

 

I want to start at maybe .050" deep and drop maybe another .025" along each line, progressing down, and then drop out the center hole.

I'm trying to figure out how to make a line or path to follow with trace or similar in the CAM side.

I usually just make 2d sketches and extrude, but it doesn't look like that's going to work here.....

Thanks for looking!

  Carl

[chrisplyler]

Your spiral path needs a bit of work before this can happen successfully, but you can loft a shallow shape to a deeper shape along the spiral path.

[etfrench]

Here's another way:

I just picked some random sizes.  Pathagorean theorem will help you determine how wide to make the offsets.

[chrisplyler]

@etfrench

Your method is cool, no doubt. But if you need a constant slope - for a marble to roll down - it does not achieve that.

[etfrench]

The marble will roll down it, it just rolls faster at the bottom

The path would need a constant exterior width in order to have the same slope at the top and bottom.

[chrisplyler]

In addition to that, slope is not even consistent on any one leg. It increases and decreases on every leg as the path gets nearer the center and then farther away from center. In fact, depending upon the pitch of the lofted coil and the relative placement of the square, it could actually slope UP on the higher legs as it gets farther away from center.

 Hey, I'm not criticizing! I don't know what the OP wants. Just pointing out the differences. They methods achieve different geometry and it might be something the OP needs to consider.

[hooverwelding]

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@chrisplyler wrote:

I don't know what the OP wants.

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Yes, your first reply is what I was looking for. I didn't have much time to play around with this yet......still trying to figure out how to make my sketches and spiral to get loft to work properly.

 Carl