Engineering drawing addendums

[GPTX]

Good afternoon,

I've got a very silly question.

Background: My company has thousands of drawings - many of which were created without adherence to any sort of standard. Due to the time crunches and the general culture of the company many drawings get sent out to suppliers without being properly revised or sometimes even released. Drawings often end up using the default tolerances shown in solidworks (x.xxx) with an additional note called out in our title block (x.xxx = +/- 0.005). These dimensions end up on all sorts of parts - wiring, copper tubing, sheet metal with multiple bends, etc. Our suppliers have learned to deal with it and typically don't question us on the dimensions (ie: copper bender knows that when we want a piece that's 12.000" with a radius 1.000" bent to 90.00 degrees that we don't /really/ need it to be like that at all).

Unfortunately this is a huge headache for the quality department because when we inspect parts they (obviously) usually do not meet the spec.

The correct action to do would be to fix the drawings; however, nobody's got the time for that. Furthermore, lots of parts are stored in older, incompatible drawing formats (ie: inventor or even autocad) so would need to be recreated from scratch to be "fixed."

So the question is: is it accepted practice anywhere in the industry to have engineering drawing addendums? I know that they're used in the construction industry where a form is attached to a drawing saying "Zone X: A should be B." Essentially this would be a quality inspection guideline which says "Drawing XXXX: Zone X, dim 0.500+/-0.005 is allowed to be 0.50+/-0.3." This form could be quickly created & attached to the pdf (bumping up the revision a minor revision letter) without redoing the whole drawing. The added benefit of this would be that the discrepancy between the drawing & the part are documented instead of what we do now (just pretend it's not a problem).

Thanks,

GP

 

[KENAT]

Some places allow "Engineering Change Requests" to be attached to drawings for extended periods.

Theory being that eventually these will get incorporated Via ECO into the next rev of the drawing etc.

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[MintJulep]

Approved Engineering Change Requests.

 

[KENAT]

Of course, thanks Mint.

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[1gibson]

A print-out of an email discussing what you really want when you get a quote, that comes in hard copy with the shipping paperwork, is better than nothing. Or set up a deviation request system where right before shipment, supplier can say "the parts are really this size, is that acceptable?" and engineer can approve it and store the form where inspection can access it (and supplier send a copy in with shipping paperwork.)

I'd start with either of both of those, and leave the Band-Aid fixes out of your engineering drawings. If "no good at all" has been uncontested for so long, you will be stuck with "well it's not terrible" forever.

 

[3DDave]

PDF is the all purpose equalizer. Convert whatever is going out to PDF and pick the tools to make the corrections. I did a few hundred that way using Photoshop to make corrections. It's no different than what was done in the previous 1500 years of technical drawings. It saves no time to have another document pasted on that everyone has to make manual incorporations of, incorporations that are not all going to match. If one of the attachments is ignored or lost it's even worse.

Other than that, good luck.

 

[tbuelna]

GPTX-

You did not mention which industry your company conducts business in. But almost every modern manufacturing business operates in accordance with international quality control standards like ISO 9001. And the uncontrolled Configuration Management (CM) situation you describe would not normally be acceptable.

There is an engineering document called an Advance Drawing Change Notice (ADCN) that is used specifically for the situation you describe. Where you want to implement a change against an engineering document, like a drawing or BOM, without changing and issuing a new release of the document itself. This is a common and accepted practice in many industries such as aerospace. And while it sounds like a good idea in theory, in practice it is not of much benefit. Below is an excerpt from "Engineering Documentation Control Handbook" by Frank Watts explaining why the use of ADCNs provides no benefits in terms of cost/effort/time.

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1434074390/tips/why_ADCNs_are_stupid_iaucxd.pdf[/url]

 

[KENAT]

A rose by any other name, at my former UK employer there were 'production permits' that preemptively allowed deviation from the drawing - as opposed to a 'concession' which was to capture deviation from the drawing after the event.

Neither of these guaranteed that a permanent design change had been approved, unlike an approved ECR.

Posting guidelines faq731-376

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(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[GPTX]

Hi guys,

Thanks for all the advice. I admit that it is a pretty terrible idea, but we need something. After further discussions today we're just going to start requesting deviations before releasing anything out of incoming inspection with the idea of drowning the engineering department in paperwork until they start fixing the drawings.

tbuelna: My industry is small-scale commercial food equipment. We are actually not ISO-9000 certified.

Here's an example of the kind of madness I get to deal with. This is a piece of "3/8ths ACR copper" (no specific metallurgical properties noted).

It gets the point across, but when quality receives it and checks the dimensions it becomes a real headache.

 

[3DDave]

You have to admit that parts that meet the print would work great. It's just that there are so many other parts that don't meet the print that would also work pretty well that suggest to people some cost reductions are possible.

I especially like the straight length dimension, because locating that transition from bend to straight is very clear.

I guess they should mention if it's annealed or drawn; also mentioning ASTM B280, unless you're not in the US.

Photoshop would make as quick work of that as an eraser on a pencil drawing. Faster than having to staple a bunch of stuff together. Even if you just pasted a note .xxx = +/-.100, that would take care of a lot of it.

You need more reactive inspectors. Call them in when parts don't fit on the line and not a moment sooner. I'm surprised it isn't like that already. Some people think a lot of money can be saved by just trusting suppliers. Some people are right. Some are very wrong.

 

[truckandbus]

we've addressed with 'permanent deviations' filed in the QA dept. When a part come in for inspection the check the file for any open deviations which modify the print requirement, signed off and approved by engineering, quality, and production. Normal deviations are specified for a specific priduction run number

 

[DiegoLGraves]

GP, coming at this from the other side, as a sheet metal fabrication supplier, when we quote work we add a standard tolerance section to the quote:

LASER/PUNCH LOCATION TOLERANCE ±.015
LASER HOLE SIZE ±.010; PEM HOLES PER STANDARD
FORMING TOLERANCE ±.030, ±1°
SAWING TOLERANCE ±.030, ±1°
WELDING COMPONENT LOCATION TOLERANCE ±.06
WELD SIZE EQUALS THE THICKNESS OF THE THINNER MATERIAL
PLEASE REFERENCE REVISION LEVEL ON YOUR PO

This applies largely to customers who have not done tolerance analysis and specifically applied the results to the drawings, but rely on standard title block tolerances. These are often point of purchase displays where holding ±.015 is not worth paying for. A purchase order for these items is acknowledgement of the terms in our quote

For our OEM customers, commercial and military, we do not include this standard tolerance section in the quote, but request deviation approval for all changes from the drawing and any listed specifications. We do not accept the purchase order (at least in theory) until the deviation is approved, or the drawing is updated.

For all work that we subcontract out, our engineering group prepares the subcontract drawing with our requirements and holds the supplier responsible to meet those requirements or request a deviation before proceeding.

This is a great improvement for us made in the last 5 years. Before that we were pretty much in the same situation you are in. We have not used drawing addendum's to address deviations. It sounds like an interesting way of documenting deviations; here we would rather update the drawing.

Regards, Diego

 

[dgallup]

That has to be one of the worst dimensioned drawings I've ever seen (although it is physically possible to make, unlike some of the stuff we have had to fix when we acquired outside product lines). I'd fire who ever made it and anyone else in the approval/release chain. That's probably not going to happen plus you would then have to find competent people to replace them. I personally like the radius dimension to the centerline, good luck measuring that. While you can handle this with concessions or deviations, etc. that just adds more paperwork and opportunities for mistakes. I would start submitting engineering change requests one by one as each of these come up. I don't care what CAD system they are in, the drawing is a defining contract and needs to be correct.

One proactive thing you could try is getting the engineering department to change their part, assembly and drawing templates to make the default tolerances big enough to provide rational tolerances for non-critical parts like this. I'm a big advocate for large default tolerances.

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