Specing Finishes and Materials

[TDevil]

I am a newly promoted "Mechanical Designer" from Sr. Draftsman (I am only 21) and am responsible for creating new standards and drafting practices for our department.
My question is: How do you normally depict finishes and materials on detail/fabrication drawings? For example, I have a bracket made of 3/8" 316 Stainless I need powder coated black. I usually denote this as notes like:

1. MATL: 316 Stainless Steel, .375 Thk
2. Finish: Powder coat, Black

Any suggestions?

 

[drawoh]

TDevil,

Your title block ought to have boxes for specifying material and finish. This is where your notes, above, go. What you have there is fine as far as I am concerned. My following notes are nitpicks.

- You should specify the material thickness as a dimension on the drawing. This way, it gets a tolerance. I must admit, I am trying to break this habit too.

- If you follow the MIL standard heirarchial naming, your material is STAINLESS STEEL 316. By this standard, your power coat specification is correct.

Please note that these are nitpicks.

JHG

 

[MadMango]

In your title block, if the material or finish cannot fit in the designated space, you can write SEE NOTES then in the general notes include the information.

To add to the nitpicking, we go a step farther and give a limit range to gage thickness for sheet and plate, as it varies form mill to mill.



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[MintJulep]

Whenever possible, your finish call-out should reference an established industry standard, especially for plating.

For paint you need to specifiy surface preparation, primer, and paint type and processes. If it is important, specifiy an exact color, either via manufacture reference number, or one of the many estblished color reference systems. You should also specify the desired finished thickness, and the number of coats allowed to get there.

As a general rule, the less specific your drawing, the less likely you are to get what you want. (and you will have no basis for rejecting the crap that the vendor tries to give you.)

To drawo's point on thickness: I agree that thickness should be shown on the body of the drawing for parts that will alter this dimension from available stock. For things that can be "made from" commonly available stock (sheet metal formings, modifications to common form stock), you should clearly state "Make from...." including reference to the defining industry standard.

 

[MadMango]

You're right MintJulep, I keep forgetting that not everyone has powder coating processes in-house.

Color could be matched to Pantone color system, RAL or to FED-STD-595.

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[ctopher]

The powder coat we call out in a note is "Powder coat semi-gloss black (No 27038) fine texture". It comes from our vendor. Material is, example: 304 CRES.

 

[McLeod]

TDevil,

Do you have a set of national or international drafting standards, or a general drafting manual, to guide the development of your internal standards? I'm going through the same exercise, and have been using the Drafting Zone website. Section 4.4 is "Specifying materials, finishes, and processes", and section 7.0 is "Notes on drawings" (based on ASME Y14.100).

Regarding some of the other comments:

- Material & process callouts can appear in the title block or in the notes. Title block designs frequently do not include spaces for this information, since adequately detailed descriptions often do not fit.

- Tolerances can be expressed in notes, as well as in the field of the drawing, esp. for dimensions which are not easily shown; e.g., coating thickness. If a dimension can be easily called out on a drawing view, then it should be.

- The importance of having a reference standard cannot be overemphasized. If an external one doesn't exist for a particular process, or if it's not specific enough, then you should develop an internal one. It doesn't need to be overly complex. For anodized aluminum, we often have the plating house provide samples at the extremes of their process, which are then given tool numbers and used by Receiving Inspection to evaluate the parts.

 

[cdub772]

TDevil,
Something I've seen at big companies, is they will write their own specifications for all of these things, materials, finishes, etc. It's a lot of upfront work, but it has several advantages:

It keeps the drawing face clean, all thats on the drawing face is a number for material, a number for finish, etc.

It allows you to provide a list of acceptable alternatives to what you want. There may be a dozen types of paint you'd take, or maybe you just have some basic critera that if they are met you will be happy with the results.

It makes it easier to translate into different languages (if not today, down the road). Arabic numberals are pretty universal, then they can get the translated version of their standard.

It standardizes what you are calling out on your print. You don't get A36, A36 M, A36 steel, A36 HRS, and on and on. If you utilize a pdm tool (or even the basic file properties of you CAD system, controlling this can be very powerful.

It lets you write out what you want in paragraph form! No more cryptic sentences where every word is ALL CAPS and abbreviated!

Also, material thicknesses should be on the face of the drawing with dimensions, just to make the point painfully clear. Tolerances can be handled in your separate spec by calling out the appropriate national standard.

Anyway, these separate specs don't have to be very long, and if you create a template up front, you can crank them out pretty quickly (it will take you a lot longer to find all the info you want in them than it will take to write them). Most I've seen are between 2 and 3 pages, with a lot of dead space for headers, footers, titles, etc.

This is just based on a couple systems I've seen that I was pretty impressed with.

The Genium Modern Drafting Manual is a very good starting point for what you are attempting, its a bit expensive ($300), but there is a tremendous amount of information in it.

Finally, your CAD package probably has some default templates that you can use as a starting point.

Hope this helps,

Cameron

 

[Cryo1]

TDevil,

Here's and example of our material and finish callouts. We put this in the note field.

MATERIAL: 2024-T(x) AL ALLOY PER QQ-A-225/6 OR SAE AMS-QQ-A-225/6

FINISH: ANODIZE PER MIL-A-8625, TYPE II, CLASS 2, (color), NICKEL ACETATE SEAL

 

[ctopher]

We never indicate material specs anymore on a dwg. Unless it is necessary. We found that the price quotes are less without them. We don't care which stock is used, it is up to the machinist. For finishes, the spec is always called out as Cryo1 states.

 

[btrueblood]

You don't care if the part is steel or aluminum (or wood?)

 

[MintJulep]

I have been known, for certain "G" jobs, to call-out:

"material: metal"

when I truely didn't care, as anything would be fine.

For real work, it always gets a full call-out to a spec, as illustrated by Cryo1.

 

[MadMango]

I would love to be able to have detailed material specs like these on our drawings. The problem we run into is our purchasing department usually goes for the cheapest mill, and we have about 5 different ones we use. Some are great, others are run like a Mom & Pop gas station.

6061-T6 for example, is it better to spec QQ-A-200/11 OR QQ-A-225/9, or is it safe to spec to ASTM-B209?

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[McLeod]

The vaguest we ever get with material specs in the medical industry is to call out "stainless steel", and then only for non-critical standard components which might be 302 SS from one vendor and 15-7 PH Mo from another. For anything custom or critical, we spec the grade and one or more applicable standards. Serious problems can occur if a material substituion results in lower corrosion resistance, strength, hardness, etc.

Mango - why not call out both standards as an either/or? We've done that for passivation callouts. QQ-P-35C has been obsoleted and superseded by ASTM A967, but some vendors still have all of their certification paperwork oriented around the old standard, so we allow either one.

 

[ctopher]

We care. We just call out the material, i.e. 304L CRES, 303 CRES, 6061-T6 ALUM ALLOY, etc. But leave off the specs.

 

[btrueblood]

Gotcha .

I did create a drawing once for a prototype, in which I really didn't care whether the material was wood, plastic, paper mache', etc. The material spec. called out was "solid".

 

[drawoh]

Cryo1,

I try to specify as little as I can get away with, although I do not think I have ever called up "METAL". Usually, if I want corrosion resistant steel, I specify STAINLESS STEEL. If I have a strict requirement of some sort, I add more information.

A danger of over specification is that people get used to the idea that you really do not mean it. Purchasing and/or your fabricator decide(s) they can make a substitution to save money or meet a tight schedule. Finally, you really do mean it and you get a nasty surprise.

When I call up STAINLESS STEEL 416MX or ALUMINIUM 7075-T6, they know I mean it.

JHG

 

[Cryo1]

drawoh,

Our standards are more rigorious that the average shop. We supply Boeing, Airbus, Lockheed, etc. and we have to know exactly what we are providing the customer. Loose specs are OK for very generic work but even then how do you know what you are getting? There are too many mom-and-pop shops that just can't produce to any standard. We must specify what we want and be exact. It's hard when a customer taps you on the shoulder asking,"What is it?" and you have to give them a blank stare.

 

[ctopher]

Military work has higher standards. For the most part they require mtl specs called out on the dwg. Other than military, mtl specs are not needed. If you have a round part and call out 304L CRES, I don't think a machinist is going to use plate stock. They know what to use. If you callout 304L per MIL-S-5059 (which I have seen), you will be questioned. Also, most likely when any mtl spec is called out on a dwg, the price quote is higher than without it. Just my experience and .02.
thanks

Chris
Sr. Mechanical Designer, CAD
SolidWorks 05 SP0.1 / PDMWorks 05
ctopher's home site

 

[Heckler]

A word of caution when calling out military specifications for materials and processes....do not callout the revision to the spec. We're tooling up for a Honeywell job and the prints callout revisions to the material specs.....trying to get a material supplier to cert material to a specific revision is like pulling nails.

Best Regards,

Heckler

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