Assembly Level Cuts - Good or Bad?

[TomU]

I would like to get feedback from the community on the use of assembly level cuts. The pros and cons, the hidden dangers, etc. I have been trained from one perspective, but I am interested in hearing the opinions of others. I am familiar with copy geometry, publish geometry, skeleton models, top down design, etc. Thanks.

Tom U.
This thread is inactive and closed by the PTC Community Management Team. If you would like to provide a reply and re-open this thread, please notify the moderator and reference the thread. You may also use "Start a topic" button to ask a new question. Please be sure to include what version of the PTC product you are using so another community member knowledgeable about your version may be able to assist.

[ptc-1932745]

Just my $.02

If the cuts are truly made after assembly, why not make the assembly cuts?
I have done this for boring holes in parts at assembly, with no problems, and it seems logical.
When you open the part models, you see the rough holes (or lack of holes). When you open the assembly the holes exist, or the holes are a different size.

But what do I know, I just heard at a user group meeting yesterday that family tables are out, and inheritance is the new hotness.


Christopher F. Gosnell

FPD Company
124 Hidden Valley Road
McMurray, PA 15317
PH:724.941-5540
FX:724.941.8322
www.fpdcompany.com
-----End Original Message-----

[cying]

Tom,
To me it's all about the design intend, show the cut at the proper level.

Calvin

[mpollagi]

I have found It will slow the regeneration time down.
But, I am a firm believer in creating the model/assembly as it
will be manufactured. This method over the last 25+ years
of what I have worked on has kept us out of trouble. There is a trade
off, I will take the slower regeneration speed over "rigging" models.







Mark J. Pollagi
Elliott Group
Steam Turbine COE
901 N. 4th Street
Jeannette, Pa. 15664
Mail Drop CB - 200
724-600-8830 - Office
-
www.elliott-turbo.com

[cprice]

I don't usually have problems with assembly cuts, but the threaded hole - thru definitely needs work in assembly.

One of the techniques I have been using when I come up with a difficult assembly cut, is to make the cut in the part, suppress it in the part and then use "make flexible" on the part in the assembly and resume the cut (or hole, etc.)

This seems to work well.

Charlie Price
Strategic Technical Services LLC
Phone 330.887.9295 Desk/Mobile/FAX
Main 888.479.1566x127
charlie.price@stechservices.com
----------

[StephenW]

If you do large assemblies, you might want to test speed of assembly cuts. At a previous job, they didn't want to use assembly cuts due to speed concerns. I personally tested it and it did make a difference but that was in Wildfire 2 or maybe even pre-wildfire. It's been a while and things might have changed.

At my present place, we do large weldments with complicated machining and sometimes multiple levels of welding and machining. We merge assemblies to do the machining. Everything stays parametric. Merge has its own issues though and I wouldn't recommend using it without doing a lot of trials and a good written procedure to tell everyone exactly how to do it and how to update it.

[TomU]

Let me muddy the waters a bit by discussing our current use case.

We have a single assembly with two parts in it. The first part is the "master" and the second is simply a mirror part. The parts are only detailed at the assembly level, but individual CAD models of each part are provided for build. 90% of the time this is fine, but recently we've had situations where changes need to be made to one of the parts, but not to the other.

Since anything done to the first will necessarily be done to the second, the workaround was to use assembly level features to modify the first without impacting the mirrored part. The problem is, if the first part is opened by itself, the assembly level features are missing (think scrapped parts). Since the assembly level features do not exist in the individual part's CAD models, the stand-alone parts do not reflect what is shown on the assembly drawing. If the assembly level features are instead pushed down into the first part they will show up in the mirror, defeating the point of assembly level features in the first place.

It seems like this needs to become either two independent parts driven by a skeleton model or the second model needs to be built with an inheritance feature instead of mirror part.

Thoughts?

[ptc-1932745]

I would go with an inheritance feature for the mirrored part, (if possible), but it sound like the 'mirrored' part is really a mirror after all, and should probably be an independent model.

Christopher F. Gosnell

FPD Company
124 Hidden Valley Road
McMurray, PA 15317
PH:724.941-5540
FX:724.941.8322
www.fpdcompany.com
----------

[dgschaefer]

You can make a family table of the master part with an instance where the features not required in the mirrored part are suppressed. Then, redefine your mirror feature in the mirrored part and select a new model, picking the instance instead of the generic.

--

[dmartin]

It's been a while since I've done assembly-level cuts, but I remember an issue around WF2 & WF3. I always recommended that people turn off Automatic Update from the Intersect tab. IIRC the problem with Automatic Update was that the cut would consider that it intersected any part that was added to the assembly after the creation of the cut, regardless of whether it actually intersected it or not. This would cause really long regeneration times, and for some reason errors on check-in to Intralink (3.x, if I recall, not Windchill).

I was consulting for a large defense company that couldn't get their top level to regenerate or check in. Once I had them turn off Automatic Update for all their assembly-level cuts, it would regenerate and check in.

Then I told them if you added any parts that you knew a cut should intersect, Edit Definition of the cut, go to the Intersect tab, and click Add Intersected Models.

I don't know if this issue persists, but take it into consideration.

David R. Martin II

Senior CAD Application Specialist

Amazon

[DonSenchuk]

Until they add the feature 'mirror except for some stuff' anyway.

[Chris3]

Behind the scenes an assembly level cut is creating family tables to turn the cuts on and off at the part level. The family tables are hidden from the user and there is no way to see them. I know this because in one of the versions of Wildfire I had one fail on me and it opened up the hidden generic. I asked PTC about it and they confirmed this is how it works.

Every time you make an assembly level cut you double the number of components in session because of the family tables. This is what decreases the performance.

[DonSenchuk]

I can confirm this, having had basically the same conversation with some PTC engineer. It creates hidden family tables in every part intersected.