GD&T/Sufficient call-outs for bent tubing prints 1

[mturner2003]

Hello everyone. Newbie here. Could someone please help point me in the right direction to acquire proper GD&T call-outs for bent tubing? Specifically exhaust tubing. I work for a small exhaust company that was built from the ground up and has all of their exhaust systems manufactured out of house. We have been using the same bender since the beginning and they did all the up front reverse engineering of tubing so that it could be manufactured. However, we have grown leaps and bounds in the past few years and are gradually starting to bring some manufacturing in house. With that said, we are also looking to get our current products quoted else where. I am their first engineer and was hired to take care of prints and to be a contact to handle all manufacturing related issues. It has been a nightmare trying to get the bender to give us PPAP documentation. It has only been recently the bending company has begin to hand over prints and they are very vague. They have given us prints with XYZ bending coordinates, but I feel there should be more to the tubing prints than just the coordinates themselves. They have us by the you know what, and are playing hard ball. I have been asked by our CEO to scan and model all of our exhaust from scratch and I am only 30% done. However, thinking ahead I will need to produce prints soon. So I found myself here asking for some direction. Sorry for such a long post. Any suggestions would be greatly appreciated. Thanks in advanced.

The print below is an example of the ONLY print the bending company is providing. So in short, is this sufficient enough to request quotes and keep on file?

 

[pmarc]

You are correct that "there should be more to the tubing prints than just the coordinates themselves".
If we just focus on aspect of proper geometry definition, it looks like the XYZ coordinates barely define a location of some points in space. The print does not specify any tolerances for location of these points, not to mention that you have nothing about bending radii. I am asuming that you at least know the size of the tube and its wall thickness.

 

[mturner2003]

10-4. Glad I'm not the only one. Our tubing ranges in size per application. Most of our exhaust are stepped to a larger diameter throughout the system to help prevent exhaust scavenging. In general our tubing ranges from 1.75" to 2.5" O.D. and are all 0.65" wall CRWST AKDQ C1008.

 

[Belanger]

There is an SAE standard that shows some good GD&T principles for a curved hose, and I suppose many of those principles can also apply to bent tubes (such as datum selection and the boundary concept for position).

Below is the link. It's kind of pricey for a not-so-hefty standard, but it's a place to start if nothing else.

[URL unfurl="true"]http://standards.sae.org/j2370_200903/[/url]

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[ajack1]

To be fair to the company that manufacture the pipes if they reverse engineered the parts the chances are they will only have the co-ordinates they manufacture to, almost old school fit and function. It is highly unlikely they will know the flow calculations or what other parts are in the way to create fully dimensioned and detailed drawings. They have done exactly what you asked of them reverse engineered and manufactured something that you can sell.

It is hard to see why they would want to give you something that they don’t need and probably haven’t been paid for so you can take work from them and send it elsewhere.

 

[mturner2003]

ajack1,

I have to agree with you. I think they merely did all that was needed to produce the part. I can understand your mindset about them fretting us taking work else where, and I won't get into how they are really sticking it to us on price, so I will keep the main thing the main thing. We as company, who are ultimately responsible for all product we sell, need to have proper drawings for all of our components. Since, I am starting from scratch, I have a blank sheet of paper, and more importantly I want to do it right the first time. To be candid with all of you, this will be first time I have ever dimensioned and detailed bent tubing. I have the skill set to complete the task at hand, yet lack the experience in this specific area.

Belanger,

Thank you for the link to the SAE standard. I am most likely going to purchase.

 

[fsincox]

JP,
Thank you for the reference!!!
Frank

 

[CheckerHater]

Second that!

 

[fsincox]

JP,
Wow, I did not know this stuff was even out there!! THIS is what I love about this place.
CH,
Thanks also for the heads up on the ISO book.
Frank

 

[pmarc]

mturner2003,
You might also want to take a look at following links:

http://www.geotolmeadows.com/newsletters/2011/jul2011.htm

- Topic: Gages That Measure Positional Boundaries

http://www.tec-ease.com/gdt-tips-view.php?q=128

They are showing some approaches to dimensioning and tolerancing for tubes. I would say that especially link #1 and the techniques defined in SAE J2370 have some things in common.

 

[mturner2003]

Every little bit helps. Thank you for your contribution. I plan reviewing the links this evening when I get home. Regards.