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Detailing Complex Geometry

Detailing Complex Geometry

Detailing Complex Geometry

(OP)
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

RE: Detailing Complex Geometry

Can you show a pic of it?
You can try section views or call out the twist, similar to a screw thd.
Hard to tell without seeing it.

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

RE: Detailing Complex Geometry

My initial thought would be showing sections at intervals along the twist like Ctopher said.

This is how I've seen it done on pre CAD drawings for aerofoil type shapes.

Depending on what standards you draw to this may be a case where Model Based Definition makes sense (ASME Y14.41).  

If nothing else you could give outline/interface information on the drawing, along with material notes, tolerances etc.  You'd then refer to the model file on the drawing as defining anything not on the drawing.  If you go this route you need to carefully consider how you are going to control the 'rev' of the model etc but it can make sense.

RE: Detailing Complex Geometry

You could put a note on the drawing saying that the CAD model controls the shape within some tolerance band.

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli
Sr IS Technologist
L-3 Communications

RE: Detailing Complex Geometry

Nice Haiku, Chris!

To define the twist:

1. Take as many sections as needed.  (Is the section a constant?)
2. Define the distance between the twist (path).

3. Define the diameter that the twist (helix) follows.

Heckler
Sr. Mechanical Engineer
SWx 2007 SP 3.0 & Pro/E 2001
XP Pro SP2.0 P4 3.6 GHz, 1GB RAM
NVIDIA Quadro FX 1400
      o
  _`\(,_
(_)/ (_)

(In reference to David Beckham) "He can't kick with his left foot, he can't tackle, he can't head the ball and he doesn't score many goals. Apart from that, he's all right."  -- George Best

RE: Detailing Complex Geometry

Thanks Heckler!bigglasses

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

RE: Detailing Complex Geometry

(OP)
Thanks Guys. I believe we will pursue the Model Based Definition. However, this is a medical device and design controls may dictate more robust documentation.

Also, the twist I described was not created with a helix. It's less pronounced. Sort of like grabbing a piece of licorice, twisting 10 degrees and raising one end.

RE: Detailing Complex Geometry

ArchusDsr,

I'm in a medical device company with FDA approved products, and ISO-9001/ISO-13485 certification.  There are no requirements for "robust drawings".  Only that you fully document what you make and change.  We have many parts that are defined in the way that looslib suggested.  Have at it. :)

Matt
CAD Engineer/ECN Analyst
Silicon Valley, CA
http://sw.fcsuper.com/index.php

RE: Detailing Complex Geometry

ASME Y14.41 is a "robust" standard. The problem is that most CAD systems don't have the features to support it completely. I would get a copy and look it over.

David

RE: Detailing Complex Geometry

(OP)
I've obtained a copy of the ANSI Y 14.41 and believe that is how we will proceed.

Thanks for the encouragment Matt. Hearing from the industry helps immensely.

Phil

RE: Detailing Complex Geometry

(OP)
Also, you are right David. The standard is rather robust, but SW2005 does not appear to be able accommodate the requirements. Does SW2006 or SW2007?

Don't ask why we are still on 2005; there's not enough room here...

Phil

RE: Detailing Complex Geometry

One thought is to show three views of the part with a axis included and provide points similar to a NACA wing.
Anyone would be able to build it from that data no matter what system they are using..

After all we made the SR71 without computers LOL


Cheers

I don't know anything but the people that do.

RE: Detailing Complex Geometry

...or so they would have us believe, thundair, or so they would have us believe.  ::que x-files music::

Matt
CAD Engineer/ECN Analyst
Silicon Valley, CA
http://sw.fcsuper.com/index.php

RE: Detailing Complex Geometry

Use of helictical cross sections are a good start, but, as in ye olden times(ink & linen) We used and auxilary views and sections to get our point across. Consistantly refering to a Doc that has been revised as many times as y14 has. Trust the force grasshopper. Think about if you are the Machineist......How would you build it? What information would get the point across? With CNC as it has evolved we can make some really cool stuff the we could not manufacter before, without some complex jig of sorts.
Regards,
Namdac

RE: Detailing Complex Geometry

Ink & linen, good times.  I only ever had to amend them not create them but that in itself was a skill!  I still recall the tales I was told of actually creating them.

In fact the drawings I was referring to on my first post were on linen.

You can describe it in 2D if you need to, just may take a lot of time & effort.  If however you can ref the model without violating whatever standards you work to (be they industry, company or just your training/experience) and the people making it can work from the model then why not use it?

I worked on one project with a fairly complex shaped conduit several years ago, (before I'd heard of 14.41 and in the UK anyway) and it basically had a drawing with tolerances, material and overall/interface dimensions plus a couple of sections to give you a general feel for the part.  It then referenced the model for the rest of the geometry.  So even if your software isn't fully 14.41 compliant in 3D you should be able to find a way around it.  I thought 14.41 allowed for hybrid model/drawing definition so the CAD systems limits shouldn't be a problem but I may be wrong.

RE: Detailing Complex Geometry

Yes, 14.41 does allow for hybrid part definitions.  We just note critical dimensions and every thing else is governed by the model (with a tolerance applied).

RE: Detailing Complex Geometry

Kenat,

It does allow for a combination 2d/3d definition but you still need to be able to give someone a model that they can query for the feature information not specified on the 2d print.

David

RE: Detailing Complex Geometry

The problem is mostly the tolerances as applied to the model.

David

RE: Detailing Complex Geometry

That's how I'd understood it and what I meant to imply by saying in both posts that the drawing had tolerances and in my second post about manufacturer working from the model.  

So as long as your 'drawing' or spec details what tolerances to use on 'model geometry' that isn’t detailed on the drawing, and you are able to export your model in a format the manufacturer can use, you should be covered right?  Maybe not as simple as it seems (especially as sometimes when creating/translating ‘generic format models’ like step, iges, stl etc things go wrong) but manageable by most 3D CAD systems I would have thought?

RE: Detailing Complex Geometry

(OP)
Back to looslib and Matt's suggestion about referencing the model; this can certainly be done per 14.41, but we make class III orthopedic implants. Class I devices do not have to follow design controls as layed out in 21 CFR, section 801.

Matt, if you produce Class II or III devices, I'd like to know how your regulatory department controls electronic files if you are not compliant with 21 CFR part 11.

thanks,

Phil

RE: Detailing Complex Geometry

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.

RE: Detailing Complex Geometry

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)

RE: Detailing Complex Geometry

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.

RE: Detailing Complex Geometry

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

RE: Detailing Complex Geometry

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.

RE: Detailing Complex Geometry

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.

RE: Detailing Complex Geometry

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)

RE: Detailing Complex Geometry

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.

RE: Detailing Complex Geometry

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).

RE: Detailing Complex Geometry

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.

RE: Detailing Complex Geometry

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.

RE: Detailing Complex Geometry

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.

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