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Detailing Complex Geometry

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ArchusDsr

Mechanical
Apr 21, 2005
9
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
 
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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)
 
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.
 
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
 
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
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(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
 
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.

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

David
 
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?
 
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
 
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