Offsetting compound surfaces

[SW]

I've had a lot of trouble offsetting and thickening compound
surfaces where the offset value is larger than the minimum radius on the
surface and so Pro/E gets upset. I then spend hours trying to modify the surface
to increase the radius while still getting the surface I want.



I didn't think there was an easy way round this, Automatic offset is usually
pretty poor, and often the outside surface is the critical one so modeling the
inside surface does not make much sense.



However, I've just found the Pro/E will offset the following surface of a
simple extrude and let the inside radius intersect itself. If it can do this,
which seems straightforward enough, why can't it do the same thing with
compound surfaces offsets?



While on the subject, has anyone got any techniques they use when confronted by
the above problem?
View attachment 2883

 

[miked]

I may be missing something but I dont get why you would use an offset as your show surface. Build the outside first and offset inwards, that will give you control over the show side and cure your offset problem. *in this case anyway.


miked

 

[SW]

Sorry, I may have confused things slightly with my explanation.
I used the image in the original post to show that Pro/E can handle self-intersecting
surfaces in some situations, it isn't an image illustration the actually
problem I'm having.



I'm interested to know why Pro/e can't do the same thing when offsetting more
complex surfaces such as the one shown below. As you suggest, I'm trying to
offset the surface inwards, but if I try and increase the offset value to that
required, Pro/E tells me the all the surfaces self-intersect and so it can't
complete the offset. Why can't it just create a point at the intersection like
it does when offsetting the simple extrusion shown above. This may cause
manufacturing difficulties, but at least I'd have a solid model with an even
wall thickness I could work with.



I'm then asking what techniques people use in this situation?
Sam


View attachment 2892

 

[miked]

Sam,

There are a couple of things you could try in these instances:

-use automatic and tweak it until you get the approximate thickness you want.

-create sections of the surface you would like to offset and create offsets of the resulting curves to use a reference for you to manually build the new offset surface

-offset the large surfaces (copy them individually first) and build the connections between them in isdx.

From the jpeg it looks like there is a strange patch on the outside surface. Its probably the odd boundaries that are causing you grief. I would try to fix that before trying anything else. You will have far fewer problems during regens.

I would also watch out for the undercuts you have along the side unless this is a flexible part.



miked

 

[SW]

Thanks mike,

The strange patch is a ISDX surface I added to the main boundary blend to create smooth end caps. Would I have been better creating the whole thing in style?

Sam

 

[miked]

I would just try to straighten out the boundaries on that patch first then.

If you have isdx I would try to build the surfaces in there. You can build it either way but you have more control in isdx, especially when you are tweaking highlights.
Its also more immediate, you can play in real time.
miked

 

[Joe Paul]

I typically find the area of minimum radius and trim a 4 sided cut from the surface to be offset. Then offset the trimmed surface and use the ISDX or bounded surface to add a small surface with tangencies to merge into the offset surface. In the case of the offset absorbing the diminshed round I ususally see this only when it can be completly absorbed. With your suface it only wants to take some of it and cant figure out how much.

 

[SW]

Thanks, I'll see what I can do with the patch boundaries. Trimming the portion with the small radius seems a pretty good idea if I'm still having problems.

Sam