If you imagine the outermost layer, unrolled, and laid flat… If you wanted that to be square, where 1mm in your drawing in x ended up being the same distance as 1mm of your drawing in y ended up being, then:
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You’d have to compute your steps/mm based on the outside radius of the object spinning. It’s a simple calculation, pi * diameter gives you one entire rotation, so:
steps per rotation / (pi * diameter) -
If you want the deeper cuts to be aligned underneath the top layer*, then you don’t need to do anything else. The key (for me at least) is to think about how much the surface has to move to make a repeated cut. If the first pass is 5cm long, and that ends up rotating it 180degrees, then if the second pass was also 5cm (the drawing hasn’t changed) then the second cut would be 180 degrees as well. The cuts will end up being perpendicular to the surface. The distance the bit travels at the bottom of the cut will be smaller than the distance it travels at the top, and that’s a good thing.
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If you don’t have the axis of rotation aligned with the x-axis, then the bit will enter the material at an angle, which is going to be bad for milling and will end up with strange results on multiple passes. It’s probably not as big of a deal with the laser, but with the laser, it will have a hard time staying focused everywhere. Just thought I’d point that out.
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If you have a material that isn’t a constant radius, then the design will be stretched/pinched when the outside radius changes.
This is completely wrong if what you want is to project the image from a single viewpoint. i.e. If you want an image that looks square when you look at it straight on. You can imagine cutting a design that you want to look correct from straight on, but will be stretched when looking at it with the blob rotated. For that, you’d probably want to do something to “wrap” the design around the object, but it really wouldn’t even require a 4th axis, You would just have to adjust the z-axis and cut with the normal 3 axes. EstlCAM has a tutorial where they cut a design into the surface of a mouse. This would be more like that. Here that is:
- I can’t think of a better sentence to describe that. But I’m thinking the lower layers are just what you would have if you just cut a lot deeper the first time.