More surfacing questions

[KENAT]

Finally making some progress in the vacuum formed part I mentioned in thread562-258988.

I have an external shape for the base part but I'm having trouble thin walling it to the correct thickness. I need .125 and can only get .068. I get the error message "Thinwall failed. The faces contain a curvature which is smaller than the offset distance" which would be fine but the radii are a lot bigger than the thickness.

Any ideas?

Rather than a thinwall do you think creating an inner surface would be more successful and doing a boolean?

I'd post the model but it was too big when I tried before. Here's a jpeg though.

http://files.engineering.com/downlo...0-a736-99701bdd27cb&file=thinwall-problem.JPG

Any help appreciated.

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[beachcomber]

Hi Kenat,
Try offsetting the surfaces highlighted individually - if that works you know they aren't really the problem.
Do you have small fillets where some of these sufaces join?
If so that could be the problem.

bc.
2.4GHz Core2 Quad, 4GB RAM,
Quadro FX4600.

 

[KENAT]

Thanks Beech.

I offset the individual faces using 'Offset Surface' and they all offset however...

They all split into multiple surfaces and the front & rear corners 'bubbled'.

Looking in the tree, all except the little 'sliver' are offset from surfaces created from variable radius rounds. As memory serves I had to use variable radius even though I use a single radii value.

I'd already looked at the small fillets and don't think that's the issue, I went back in the tree and tried doing a thinwall before adding them and there were more problem surfaces highlighted when it failed.

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[KENAT]

Oops, meant to attatch an image.

http://files.engineering.com/downlo...a-b7a3-0e908c68fbce&file=individual-faces.jpg

Also, to say thanks and if anyone has any more input, it's appreciated.

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[HDS]

You can try using surfaces for the radi instead of rounds.

Which side of your model will be used to cut the tool? Is it a male tool using the inside surfaces or a female tool using the outside surfaces? Those are the surfaces that will really make the part and have to be perfect. The other surfaces are only used in your model. This is because in the real part they made by the sheet and the thickness will not be perfectly uniform. Did I explain that well?

That said the accuracy of the other surfaces can be reduced. So if something does not offset well you can delete the bad part and model it in a way that works. This might give you non uniform wall thicknesses.

NOTE: if you are using a two sided model such as an injection molded part than both sides must be perfect. Also uniform wall thickness is very important for the molding process.

 

[KENAT]

Interested what you mean by using surfaces instead of rounds. I tried using blended surfaces instead of variable radii in the round command. Are you talking about sweeping a surface along the face intersection or something?

I'm just showing one of 5 'parts' that go together to form finished article. It's a bit of a russian doll situation with molded in liners which is why I'm modelling from the outside in as it were. Also it has a access cover that closes up the opening.

It will actually be a male mold for this part so yes the internal surfaces are arguably more important from that point of view. I fully understand what you mean and have been trying to keep the essence of that in mind when modelling, though maybe I've missed some nuance.

Also, this is a very aesthetic part and everyone upto the division VP wants to give input on it. It started out as a very simple shape based around suiting the manufacturing process then we had to get an industrial designer look at it and now it's more complex, though admittedly prettier.

I have a rough external outline model from the industrial designer (made in SW and I only have a step of it) but it has been modelled without really taking account of some of the finer details of the manufacturing method.

So I'm basically trying to take the ID pretty design combining it with some changes requested by the VP and address manufacturability.

Thanks for the help.

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[HDS]

Yes blended surfaces or sweeps are both options.

I would model the male surfaces first on the next part. That will be easier anyway because most of the offsets will get bigger.

If the outside surfaces will be textured or smooth or painted makes big differences in the details of the model. The flow of one surface into another or the rounds is more important with a painted part.

 

[beachcomber]

Try replacing the wobbly surfaces with new ones. You should be able to do those with blue-surf using top & bottom curves as the cross-sections and the side curves as the paths.
Alternatively, use a surface by boundaries and I think you can get tangenciy with the surrounding surfaces.

bc.
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[KENAT]

Blended surfaces instead of variable radii in the round command didn't work when I tried it on a couple of them.

The part will be painted to look similar to covers on other tools.

The way the part is shaped, to fit it's eventual 'contents' it's conceptually simpler (at least for me) to model the exterior surfaces first. However, if I can't crack the nut that way I'll have to try the opposite approach.

I replaced wobbly surfaces on some of the earlier face offsets. If I can't get the thin wall to eventually work then this was the approach I was looking at but thanks for confirming my thoughts.

Thanks both of you, just to further complicate things my manager just came by all excited about the EM sheilding of it.

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