Detailing Complex Geometry

[ArchusDsr]

We have a part that is very complex. Our vendors can make if from a parasolid, but we have yet defined it on a drawing. The part has three features; one end is slotted and flat, the other round and tapered. In between is a complex twist extrusion. Overall length is about 2 inches. How can we detail the twist? Does anyone have sample drawings?

thanks,

Stumped in Seattle

 

[ajack1]

I always wonder why people want to do this?

If a company can machine to a solid model they will, even if you can cut enough sections and show enough points to create a cutter path they will never be used, no machinist is going to start trying to create new geometry from a 2D drawing when they have perfectly workable 3D data.

Other than adding many hours to the job and the possibility of the drawings being misinterpreted what use are they? Of course you need to show tolerances.

 

[ctopher]

A lot of companies have to have something to check against.

Chris
SolidWorks 07 3.0/PDMWorks 07
AutoCAD 06
ctopher's home (updated 03-26-07)

 

[ajack1]

Then why not use the model? At least as I see it about 95% of the advantage of solid models is you design them, run any FEA on them, machine to them and check against them.

 

[fcsuper]

Archus,

Our rating is for diaganosis. I'll apologize for not immediately knowing the actual standard we hold to. However, the solid model is as much part of the control as the drawing. At the risk of making a general comment, I will say that many engineers these days are actually uncomfortable with drawings all together since the design intent is captured best by the solid model itself, and the drawing is only an interpretation of that solid model, thus creating a second layer where mistakes can/will occur.
Beyond this, I can't answer further if you need factual specifics. (I guess I can say that I do not believe that the FDA has any drawing standards at all.) From my experience, it's up to the company to determine their own system, and the FDA simply checks that system against a very specific publically available audit check list.

Matt
CAD Engineer/ECN Analyst
Silicon Valley, CA

http://sw.fcsuper.com/index.php

 

[KENAT]

I know places do use the model as the master, hence 14.41 etc but I will admit I still have concerns based on the fact that I've seen a lot of lousy models. You know the kind that when you try to revise them for very minor change the whole thing falls apart and you have to rebuild it.

I've also seen a lot of poor control of model & electronic drawing files.

The latter problem can probably be solved with either PDM/PLM or just good practices & procedures but I'm not sure about the former. The only really good configuration control system I've ever seen relied on signed hard copies of drawings(which did get scanned afterwards) but this seems archaic.

I would have thought that for an application like medical you'd have to have these areas covered. I would think that having a drawing, be it a partial one, was one tool to help with this.

ajack1, not everyone can fully check against the model. Also sometimes it's useful to have the option of just checking certain critical dims without having to put the part on a CMM machine. For this you either need an annotated model to reference or a drawing. Otherwise you’d have to interrogate the model which can be time consuming.

 

[ajack1]

Sorry KENAT but I cannot agree, if I want to produce a cube with a hole in it then yes I could use a mic, vernier, DTI or many other ways of checking it, and as such a 2D drawing may be of some use. However the OP’s question was about a “complex twist extrusion” now just exactly how are you going to check that except on a CMM?

I still cannot believe companies can waste this amount of time and money and still be in business.

 

[ctopher]

In a lot of businesses, a drawing is required for checking a product between a company and their customer. most companies and their vendors/customers do not share the same CAD software, or the knowledge of them, to check against the model. The dwg can be shared, stamped, signed and filed for parties involved to see.
I also agree with KENAT.

Chris
SolidWorks 07 3.0/PDMWorks 07
AutoCAD 06
ctopher's home (updated 03-26-07)

 

[ewh]

I'm afraid that I don't agree here. The fact that a model was poorly constructed only affects the editing of said model. We have inspected to unparameterized parasolids for a while. There only purpose is for customer use and our inspection. Soon we will be migrating to have the ability of inspecting to the native models, and the situation will not change for inspection, other than our having to control one less model file.
As for a poorly constructed model, that is another issue, and should be addressed by training and company standards along with vigorous checking of the models before release.
I am not familiar with FDA requirements, but do know that FAA requirements now allow a completely digital definition for aircraft.

 

[KENAT]

This may be getting off topic but:

ewh, I was talking about editing of the model, this combined with poor file storage/config control practices can lead to problems. However, of course the same thing can happen if you lose the master drawing in old school systems so it's not specifically just a 3D issue. Although I’d think re-creating a drawing (and associated model if applicable) from a print may be easier then doing it to a dumb model. Given that drawing check has more or less gone the way of the Dodo in the 2D world, do places that rely on MBD really spend significant time auditing models? From my experience this could be even more time consuming than checking drawings.

As regards checking certain critical dims without CMM, many if not most of the 'complex shape' items I've looked at in detail still have interfaces (especially mounting points) somewhere with not so complex shaped items and it can be useful to check these interfaces with non CMM inspection methods. I’m not suggesting you try and check the complex shapes with it but for instance it may be you have a part on which you want 100% inspection of the mounting hole interface, which can be achieved with Vernier etc, while only every 10th, 50th or 100th… needs the complex area inspected.

I know plenty of people are making MBD work and presumably more efficiently than just using the model to feed 2D drawings or they wouldn’t still be doing it. However, I’d really like to understand how they make certain aspects of it work. I wasn’t saying the OP shouldn’t go MBD, in fact I was the first one who brought it up, I just think there are issues to address and I’m not sure I even know all the issues, let alone the solutions so was hoping posters that use MBD could elaborate, both for the OP benefit and for others (including me).

 

[KENAT]

Looks like thread1103-182896 may be a better place to continue the aspect of the thread regarding advantage of MBD and any problems/issues that need to be taken into account.

 

[ewh]

I do agree with that, KENAT. It boils down to a configuration management control issue. Some CAD systems let you "check" aspects of the model before you release it, and this can go a long way in easing the burden of model auditing.
Most of the parts we make do not have "simple" interfaces that lend themselves to non-CMM inspection, but I do agree with where you are coming from.

 

[KENAT]

Yes, I think many/most of my concerns are either explicitly or implicitly configuration control issues rather than product definition issues as such.

My current place barely has the configuration control standards adequate for the drawings which are fed from models. I can only imagine the mess it would be if the model were the master. In fact our sister site does use the model for some complex castings etc and have had configuration control issues.

I used to work in Aerospace/Defence in the UK. Our confguration control for the printed out, signed off drawings was probably the best I've ever seen, and I've done work with major US contractors. However the control there for the original CAD data was almost non existent.

My current commercial place in the US treats the CAD data as master and relies on 2D drawings fed by 3D models. However while they do manage the data it's not very rigourous and in my opinion no where near rigorous enough to support MBD.

I may post on the other thread to pose the config control questions but better go do some work first.