Negative of a model

[kstrauss]

I have a customer supplied 3d model (.STL file) that I have successfully milled using VCarve Desktop. He now wants the negative of his model. That is, he supplied a 3d model of an ear and he now wants a mould to cast ears. Any suggestions regarding how to do this? Hopefully this is clear; he considers the model proprietary so I can't post it here.

[4DThinker]

A negative mould might be better created by doing a silicone casting of the positive model.

[garylmast]

A negative model would probably have undercuts, where it would require slicing and doing a double-sided job. Not seeing the model but I don't see a big problem do it.

Gary

[kstrauss]

Yes, undercuts on an ear mold would probably be an issue; mentioning an ear was a poor example. For this particular job the 3d model is more like a coin so there would definitely be no undercuts required for a mold. If I can adjust the model to be a negative there should be no problems cutting it.

[FixitMike]

I am unable to visualize how a positive model without undercuts will produce undercuts in a negative model.

In any case, if you use the subtract mode to combine with the base material it will be a negative model.

[WNC_Ed]

This sounds like exactly what you need
Vectric | Live Stream - Two Part 3D Mold - Dragons Claw

https://www.youtube.com/watch?v=D9B9VOpSAPg


He does everything in positive and then switches to a negative.

[WNC_Ed]

Working link this time:

https://www.youtube.com/watch?v=D9B9VOpSAPg

[kstrauss]

Thanks WNC_Ed; that is exactly what I was looking for! For anyone reading this thread in the future the "How to cut a negative" information starts around the 34-minute mark in the video. Note that although one is not warned you will have to recalculate your toolpaths after making the changes described in order to get the desired results.

[WNC_Ed]

Awesome, glad it helped.
Hoping you can share pictures at some point.
But we understand if it is proprietary.

[martin54]

Just to add, not sure what the tutorial says, haven't watched that one in a while but if you are machining a model below the material surface then you will need to add a zero plane

[kstrauss]

Thanks for the reminder. The video STRONGLY recommends adding a zero plane.

[kstrauss]

I would normally be happy to post pictures but not in this case... The parts are aluminum pieces for a pneumatic rotary vane actuator and the "reverse" part is an O-ring retainer that matches the curve of the body of the rotary vane. See for a video of a competitive design which is similar to what I need to cut. Definitely not your average sign with a 3d rose in the corner!

[mtylerfl]

Went from an ear, to a coin and now to an actuator. Must be a mighty interesting-looking part!

[kstrauss]

An ear was a poorly chosen example of what I wanted. A coin demonstrated the true problem. The video is what I'm actually making!

[TReischl]

Actually is for an alien space ship in Area 51, ET has phoned home.