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I'm trying to create a persistent boolean on an animation of two cylinders rotating and I want one of the cylinders to imprint the block onto the other cylinder. I have created a short demo below with standard animation boolean.

Example of two cylinders

https://youtu.be/jEWE13mABYY

Is boolean the right modifer? Is there a tool/modifer that would be better in this circumstance? Do I need to use python to boolean and apply each timestep? Has anyone done this before?

I realise this is very niche. The intention is to 3D print the cylinders of the final result.

EDIT 2025-09-08:

I ahve been told another way to do it is to create a volumetric sweep of a solid body along a curve and then boolean that curve from the original. However I don't know if blender can create a swept solid from another solid...

Here is an example that has been tried in Rhino https://discourse.mcneel.com/t/plugin-or-rhino-tool-for-swept-volumes-sweeping-solid-bodies-not-curves/59934/8

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  • $\begingroup$ blender.stackexchange.com/questions/79445/… $\endgroup$ Commented Sep 3 at 9:03
  • $\begingroup$ Thanks Duarte, its essentially a different example as the shape of the boolean in the example is known. As I'm rotating and interferring the "square", which a proxy for something more complete will leave an imprint that is an unknown shape. Its that unknown shape that I'm trying to extract. $\endgroup$ Commented Sep 3 at 9:49
  • $\begingroup$ It looks to me like it would essentially be a Gear Tooth shape, maybe you can calculate it mathematically duckduckgo.com/?iax=images&ia=images&q=gear+tooth I can't immediately think of an easy method to obtain it directly, but maybe a solution using geometry nodes and a simulation zone could do it. beware that boolean based stuff will inevitably be inherently unstable and heavy $\endgroup$ Commented Sep 3 at 10:23
  • $\begingroup$ For gears it is a revolute profile.. I'm actually going to be using all sorts of shapes so I can't calculate it geometrically $\endgroup$ Commented Sep 3 at 10:49
  • $\begingroup$ In that case I suspect only some sort of geometry nodes simulation can help there $\endgroup$ Commented Sep 3 at 12:09

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You could create a copy of the "printer" (make it invisible in render) and use "Child Of" constraints to suddenly change this printer from rotating with cylinder 1 to rotating with cylinder 2:

Child of Result

This way, you use the "printer" copy as the boolean object (you can simplify it later in edit mode, if you want)

How to parent

The process of parenting them can be tricky and must be done following a strict order to avoid complications. It can get pretty confusing if you don't follow this order.

Let's name things:

  • Original: the original cylinder that has the block
  • Copy: the copy of the original cylinder
  • Printed: the cylinder that will have the hole

Sequence:

  1. Go to the frame where you want the copy to be part of the printed (from this frame on, the copy will be following the printed, before this frame it was following the original)
  2. Duplicate the original to make a copy (don't move it)
  3. Clear the animation of the copy (and don't change frames)
  4. In the copy, add a "Child Of" constraint, set the "Target" as the "original"
  5. Move one frame back
  6. Keyframe the "influence" of the constraint
  7. Move one frame forward, set the "influence" to zero and keyframe it
  8. Add another "child of" constraint, now the "target" is the "printed"
  9. Keyframe this new constraint's influence
  10. Go back one frame, set this new influence to zero and keyframe it

Done, now use the copy for the boolean and hide it.

Final Result

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  • $\begingroup$ Thanks for the effort, however it is not what I'm looking for. I'm looking for a mathematrical cut in the geometry that is not predefined, but rather made by the kinematic motion. I will update the question to explain it better. $\endgroup$ Commented Sep 8 at 15:40

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