cavity feature

revisions to a

inconsistent

John, all I can say is you need to get with your VAR and this needs to get ironed out quickly in the next Service Pack (hopefully SP 1.0 due out soon).

Bo

John, it just may be that putting in a cavity with "0" shrink is what might cause the problem, if SWks programmers didn't consider that some people do NOT want to use shrink in that way.

Worth checking.

Bo

Bo,

You never have been able use it because it works as an offset and not a scale. It makes the cavity the right size, but the core is 2X the factor too small. I guess they'll never fix it at this point.

I've been scaling parts and using "0" shrink for years, never had a problem. I think it has more to do with some rebuild weirdness myself. 2005 rebuilds way to much when it doesn't need to, and not at all at times when it does. Go figure

Mark

Any surfaces in your model?

Was the cavity feature originally created in 2005?

-Jason S.

Hi jk Very seldom has the cavity feature failed on a "rebuild" once it has been successfully completed (for me anyway). I normally run the cavity routine on a raw block, then I use the block as a "base part" for my cavity "components" putting in partingline cuts, waterlines , etc. I then use those "components" for my mold assembly. This way the "cavity" feature is not in my "mold" assembly, saves on some rebuild times. Since the "cavity" routine is in a different part away from the "mold assembly" it never has to rebuild unless "raw block" has been modified. I'm sure you were aware of this, but I thought I'd put it out there for any newer mold designers. Just another way to "skin a rabbit"

Mike

Yes cavity feature and also the original part were created in 2005. Really simple part, too with no surfaces.

I did indeed contact my VAR and sent in a file with instructions on how to break it. They have not confirmed it yet, but they are buried in stuff from people yearning for sp1.

Here is the workaround they suggested and it did indeed work, but there is still a bug in there. I always work with the `verification on rebuild' box checked. If I go into my options and uncheck that box, then I can open my assembly and make the change I was trying to do and everything re-builds with no problems. I can then save and close; go back to options and re-check the box; open the model; do a ctrl.q and everything is still fine and I proceed.

This is a bug.

In regard to that verification box, I have found that I get corrupted models eventually if I leave it unchecked. Also, I sometimes get a SW part for a mold design and it won't scale for shrinkage-SW tells me that doing so would result in inconsistent geometry. When I call the engineer who modelled the part I always ask about that verification box and in these cases they always say that it is unchecked. I see this as proof that this should remain checked. Only way to proceed with models like that is to roundtrip them through parasolids;run import diagnostics;fix bad faces and THEN I can scale it for shrink. I lose features, but at least I can get a model.

Anyway, that is off the topic in a way. Thanks for the replies.

jk

inconsistent

Yes, that is exactly the way I usually do it too. This part was really simple and `in-the-solid' in a MUD base. The quickest way to deal with it seemed to be to just stick it in there and do the cavity at the same level as the design. Just more confirmation on why this is not a good idea.

jk

inconsistent

Damn! What in the heck is wrong with SolidWorks programmers if "Scale" doesn't work right? I mean, how basic a task is that. In fact why leave it in if it is NOT right?

I obviously do not understand what is wrong with the Cavity Feature! This is scary.

Can you describe easily how you get a non-equal scale when using Cavity?

There is more going on here than I thought. When I have checked, my cavitie's scaled sizes came out right when I embed a model in a block and use the cavity feature.

Bo

In my 2nd sentence "...if "Scale" doesn't work right?", I obviously wrote too quickly and it should have been "Cavity Feature's Scaling" doesn't work right.

Obviously the stand alone Scale feature is working right.

In some situation Cavity Feature's Scaling does NOT, but I am confused on that part.

Thanks - Bo

Bo,

I was talking about the "shrink factor" in the cavity dialog. It uses offsets so the female cavity gets bigger (right), and male core gets smaller (wrong). It's only half right. It's been this way forever, and is totally usless for mold design.

What I've allways done is apply a scale to the part, and subtract the core/cavity features usink "0" shrink factor.

Non-uniform also doesn't work right with regards to molds. It turns bosses with circular cross sections into ellipses. We both know an ellipse isn't going to shrink into a circle. You have to manually edit these features to make them circular again. This was probably just a generic Parasolid function that they simply turned on, without taking the time and effort to make it usefull. It's also very sensitive to marginal geometry. Your model has to be clean.

Regards

Mark

Cavity Feature's Uniform Scaling when a model is put inside of a single "block" seems to work correctly.

Hence, I am still unsure how to do the "male core gets smaller" routine.

Thanks - Bo

Bo,

Well,,, I guess I gotta eat my words on this one, they fixed it (sorta). I don't think I've tried it since SW99.

It still has problems though. If your subtracting the whole part from a solid block, and then cutting away the parts, it works correctly. This , however, will only work for very simple parts. If you build up the core and cavity inserts from two seperate pieces, like I do, it becomes a problem because the "cavity with shrink" operation wants to extend the edges of the parting line. Much easier (for me at least) to use a scaled configuration of the part. There's alot fewer potential rebuild errors.

Another possible source of our mis-communication would be if your using "mold tools". I don't use them. I played around with them in 2004 and 2005, but couldn't see any benefit. Mold tools creates to much unnecessary geometry, (surfaces), and most of what I did with them was prone to rebuild errors. I guess they figured that most mold guys are used to working with surfaces that way, and designed the tool based on these ASSumptions. The truth is, I can (most times) create cores and cavities without using surfaces at all. Sometimes reference surface for the parting line, but that's about it. This results in a much more robust (hate that word, to "geekish") mold assembly, that rebuilds correctly when changes are made to the model. This is important to me because, sometimes, I'll have to design the tool before the parts are finalized.

Regards

Mark

Mark, that bit about more stability using the cavity feature vs. surfaces is exactly why I don't like the mold tools.

They basically now have a tool that doesn't do anything well except demo well with a pre-selected part. I bet there are some pretty frustrated new users who thought they were getting automatic core/cavity generation.

jk

JK,

Yea,, It's pretty useless for real molds.

For years mold designers have been have been shouting for better "surfacing" tools to design molds. Most of these guys were probably used to designing molds in CAM packages like Cimatron, Mastercam, or Powershape. They responded to the shouting litteraly, instead of taking the time to think through a "smarter" way that took advantage of the SW environment.

You have to be carefull what you wish for I guess

Regards

Mark

configuration

Mark & John, I pretty much agree with you guys. My plastic parts I design gain nothing from using sophisticated tools which are more prone to errors or limitations of one type or another. I, too, virtually never need to use surfaces for my types of parts.

I don't design molds any more, but I need to be able to accurately plan layouts for all sorts of things (some indeed 'weird') with multiple sleeves and core pins and removable inserts, water jackets, etc. and need to be able to 'rough out' a cavity set layout before I take it to the mold maker. I would look real foolish if my use of Cavity Scaling for shrink were off for simple parts.

As a side note, I have watched the use of "organic" cell phone shapes come, and, now somewhat surprisingly, receed into the background. I suspect the manufacturing issues and costs associated with making weird shaped cell phones weren't worth it to consumers and the manufacturers listened.

I don't care what software package a designer uses, it is going to take a lot more worki creating all those off-beat curvy 3D shaped mating parts with all their little mating, assembly and locking devices.

Bo

Is it possible that those shapes just weren't what people wanted? Personally, I think a somewhat blocky shape is easier to handle than many very curvy ones.

getting pretty far from my original topic here, but SW has indeed improved it's surfacing capability in areas that I regularly take advantage of. Untrim is a fantastic tool. I also use `replace face a lot. I am starting to use the `move face' function too. All of these little tweaky features weren't around until recently and I appreciate having them.

It's the full-on surfaces approach to core/cavity split that I think is being applied wrong by SW. On the other hand SplitWorks also uses a surfaces based system and it works pretty well. It's all in the way the application is implemented.

jk

JK,

I agree. Surfacing has improved alot, and I do take advantage of it when appropriate. I look at it as more wrenches in the ol toolbox.

As far as thier implementation, it is pretty lame. Myself, and others, have offered to collaborate in the development of usefull mold tools. Never got a response. I kind of get the feeling that ther person responsible has read books, and had molds carefully described to them, but has never seen one first hand.

Regards

Mark