Scaling an object

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1

I’m after some advice on scaling an object so that I can create two objects that fit one inside the other with a uniform thickness space between them.

Essentially I need to create a mold and a plug to layup fibreglass and resin between them and compress the layers firmly together while it cures.
The mold has been drawn as the primary working object and a reverse solid block created from it with a larger block and the subtract tool.

The negative is the exact size of the inside of the old and needs to be scaled down so there is a 2 mm separation between the mold and the plug.

I tried to simply scale smaller that inner “negative” block so that it could be positioned to leave a known space inside the mold.
The problem is there are several protrusions on the final product and on therefore on the plug.

When the whole plug block is scaled the protrusions move “centrally”.

What I really need the centre of the protrusions staying fixed and the protrusion getting smaller concentrically. ( sorry, hope that makes sense)
What happens with scaling is outer side of the protrusion moves inwards (the correct direction) but the inner side also moves inwards then impinges on the mold.

Is there a method of scaling the plug so that the surface scales “inward”.
Sort of like a solid version of the offset sketch tool?

2

So do you just need tolerance between the molds?

3

If tolerance is needed you can shell.

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Subtract

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4

Hi John,

A tool that might be work for this is Shell. That will give uniform thickness. You may still need to do the reverse solid block again.

A picture could be useful…

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5

Thanks for that. Great idea.

I think that will work. Will try and let you know.

The only problem I could run into will be if the SHELL won’t work on the first block negative.
Something I’ve noticed recently is that the shell command ( in fact a lot of commands - fillets, extrudes especially going in the negative direction and some others ) seem to be very prone to fail once your have done even minimal changes to the original object.
I get the feeling it’s part of the many crappy side effects of the parametric capabilities of the more recent versions of the app.