Why Won't This Fillet?

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 From:  OSTexo
4249.1 
Hello,

I'm building an AC adapter using a combination of MoI and SCE. I am trying to fillet the back of this to 3mm. For some reason this doesn't work too well in SCE or MoI. Interestingly it works when I set to 3.01mm, but not 3 exactly. For some reason when I apply a 3mm fillet to the entire model it works fine, but I am unable to use the variable radius fillet in SCE. Thoughts? Thanks.
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 From:  Frenchy Pilou (PILOU)
4249.2 In reply to 4249.1 
sorry what is SCE ?
---
Pilou
Is beautiful that please without concept!
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 From:  OSTexo
4249.3 
Hello,

Spaceclaim Engineer
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 From:  Michael Gibson
4249.4 In reply to 4249.1 
Hi OSTexo - the difficult situation you've got there is trying to apply a second fillet that tries to hug the contour of the previously placed fillet at the same radius.

That kind of creates a situation where the fillet is collapsing down on itself, it's kind of degenerate situation.

I'm talking about the fillet surface that is going to be attempted to get constructed between these 2 faces:



You can kind of get an idea of what is difficult by starting with a smaller radius and making it progressively larger.

Here's with radius = 1:



Here's with radius = 2:



Here's with radius = 2.5:



So notice as you approach radius = 3 the edge on this side is basically collapsing down:



That kind of collapsing creates complications - particularly in a case like you've got here where the surrounding surfaces are a bit swoopy and not just at an exact 90 degree angle to one another. The previous fillet kind of has an upwards swoop to it which you can see if you look at it in the Right-side view:



Because of that swoop there will be some differences in spacing and alignment between the fillet pieces with kind of one side not quite collapsing down to the same point as the other side within the same fillet surface piece, until you go to a bit higher radius, that's why something like that can start to work again at a higher radius.


When you do the whole object, those areas where there is a collision between 2 fillet pieces of the same radius get done with a special corner-patching technique instead of it trying to actually build a regular tubular kind of fillet surface between them, that's why you can see different results when you do a fillet all in one go instead of in separate stages. It can be difficult to a fillet of the same radius that collide into each other in multiple separate passes instead of all at once because of this.

I'll see if I can come up with some tips for you on how to finish the construction.

- Michael

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 From:  BurrMan
4249.5 In reply to 4249.4 
A Constant Distance fillet of 3mm will go on it if that will work for your situation.....
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 From:  BurrMan
4249.6 In reply to 4249.5 
You can create a different kind of corner patch on it also by applying a 3mm fillet to just the 2 verticle edges first, then applying a G1 fillet to the top horizontal edge:

EDITED: 19 Jun 2012 by BURRMAN

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 From:  Michael Gibson
4249.7 In reply to 4249.1 
Hi OSTexo, I've attached a version that I finished up by splicing together some pieces.

I separated out the top surface and untrimmed it and then stretched up the side walls and then retrimmed it to get back to an original sharp corner shape like this:



Then filleted that, doing those areas all at once to make this:



Then kind of harvest these faces here and paste them into your other model and trim the other model to splice them in:



One tricky part with this is that the fillets made by Moi and SCE have slightly different rotations to their cross-sections, so they don't quite meet up directly - I had to erase the longer fillets along the upper sides and replace them with a sweep to make the pieces meet up easily.

- Michael

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 From:  OSTexo
4249.8 
Hello,

Thank you very much for the tutorial, it worked flawlessly (as usual). I saved my original rough versions of the model so following the steps took just a few minutes. I made some modifications to the model and the variable fillets to more closely match the actual adapter.


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