【转帖】specing finishes and materials

yang686526

specing finishes and materials
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?
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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
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.
but what... is it good for?
engineer at the advanced computing systems division of ibm, 1968, commenting on the microchip.
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.
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.
but what... is it good for?
engineer at the advanced computing systems division of ibm, 1968, commenting on the microchip.
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.
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
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
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
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.
you don't care if the part is steel or aluminum (or wood?)