Surface Offset for mold 4

[ctopher]

I mentioned in an earlier thread that I'm somewhat new to surfacing.

I have a finished part that was created with complex surfacing, I can not change it.

Now, I have offset these surfaces inside to create a mandrel for molding. The complex surfaces don't like to offset very well. Per the pic you see some surfaces are not smooth and there are gaps where the final part has radii.

Are there other methods besides using offsets to create molds for the internal geometry of the part, or how can I fill these gaps? I tried all surface commands like boundary, filled, etc, none work.
I prefer to not use offsets because there are too many surfaces and too many additional steps to fix the offset's overlapping surfaces.

The dark areas are the gaps I need to fill between the 'stepped' surfaces.

Chris
SolidWorks 09 SP4.1
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[TheTick]

Scale?

 

[ctopher]

Full scale model. The picture is probably 2X scale of part.

Chris
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[ajack1]

This is what happens if you create bad surfaces in the first place, you will either need to recreate them with proper tangency etc or offset them and then spend a good amount of time fixing them.

 

[TheTick]

I mean can you scale the model? Many of the mold makers I have worked with account for shrinkage by scaling the model.

Looks like there's a little crud from surfaces not being well-knit. Or is that just the picture? You may end up needing to offset the surfaces individually and extending/ trimming/ knitting them.

 

[ctopher]

I agree the surfaces are bad in the part model, but I can't change them, nor will the originator.
I tried scaling the model, does not work. Scaling will not be proportional overall. I have to offset, then add material to the length for shrinkage.

Chris
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[Theophilus]

Those surfaces are bad. This often happens if you scale in a direction that requires concave areas (such as radii) to shrink in radius very much--there's only so much you can go before hitting zero.

If the whole thing isn't scaled, perhaps you can identify areas that are scaled. Separate your model into chunks (solid bodies) by splitting, scale the chunks you can scale, and then join the bodies again. A bit of a hack, but it might work fine, depending on your limitations of scaling.



Jeff Mowry

http://www.industrialdesignhaus.com

A people governed by fear cannot value freedom.

 

[ctopher]

I tried the scaling, but it doesn't proportionally.
Thanks for the help.
I'm going to have to fake and redo some of the parts.

Chris
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[ajack1]

If it started out as imported data it is well worth spending some time “messing around” with the import / export options as this is where many of the problems can start.

This is especially true with iges where everything comes in NURBS and much of the tangency is lost, I always try and avoid iges if at all possible. Again if the part is modelled a long way from carline this does not help, tweaking the settings can improve this.

If you start of with bad data the problems just get more and more as you try to offset, it is well worth spending some time up front fixing the data it will save you hours down the road. Not to bad on a simple part like the one shown but a real nightmare on anything complicated.

 

[ctopher]

No imported data. The part file that I'm doing the offset from is all surfaces created by our parent company, and it can/will not change. I'm stuck with what they send me. Sure I can modify it, but 40 lashings will follow...I'm also only contract here.

I have to fudge it somehow. Thanks!

Chris
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[TheTick]

You must modify it, at least to repair the scar tissue at the seams. Otherwise, you will waste many painful man-hours.

 

[ctopher]

Yes, I know.
I'm stuck.
Thanks anyway.

Chris
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ctopher's home
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[mjcole]

Chris,

You might try doing a Delete Face with Tangency or Boundary Patch. If neither of those work Filled or Boundary Surface can maintain Tangency and Curvature conditions on boundaries.

It may be impossible or be hard to come close to their crappy model But you can make a 0 distance Surface Offset (copy) feature of the original surface prior to the Delete Face command so you can compare the geometries using SolidWorks Utilities.

Other options.
Get a 3D Print made and sand it down and scan it.

Michael

 

[pierdesign]

for this sort of a job unfortunately it must be repeated:

best way is to have a robust contiguous model first, scale, offset surfaces 0, build other surfaces, trim, knit into solid(s).

Sorry if that doesn't work for you. As you know there are many ways to do same thing, so try again to achieve above result.


Regardless, in Solidworks surfacing, I have resolved to default offset surfaces 0, extend them, frequently individually, beyond required dimension to intersect other offset or built surfaces, then trim and knit to solid.

I have noticed a persistent bug in Solidworks Surface-Extend: frequently it extends linear and contiguous tangent curved surfaces illogically. Delete and try again (not edit existing) works, extending contiguous tangent surfaces evenly.

Surface-Extend up to surface rarely works; always extend beyond to intersect, trim, etc.

If I build a sketch driven surface its dimensions will always be beyond what is required, then trim, knit, etc.

Solidworks surfaces love to orphan themselves like a suicidal cult from their parent child relationship. This is why I repeat others in first statement - best to have robust valid model, scale, offset 0, etc.

If you haven't worked a lot with Solidworks surfaces expect to have the feature tree grow exponentially. Grouping like features into folders, coloring surfaces differently, regularly turning on/off surface / solid bodies - all common.

 

[ctopher]

mjcole,
I have tried all of those commands. The 0 offset first is a good idea, thanks.

pierdesign,
I have been grouping them into folders because there are a lot. Thank for the suggestion.

Chris
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