DReimer
Mechanical
- May 20, 2005
- 55
I'd like to survey the participants in this forum regarding material callouts on part drawings. I'm especially interested in companies that design and fabricate their own parts (rather than design only).
Our company uses an MRP system, and as such every raw material we use has a part number. Our raw material part numbers are significant - e.g. ALF3/8X2 is, you guessed it, aluminum flat bar 3/8" thick by 2" wide.
Our tradition has been to call out the actual RM part number and quantity on the title block. If, for example, we design a part from aluminum and it is 3/8" thick and 2" wide and 7" long, then we would call out ALF3/8X2 (x7.00) in the title block (provided the standard mill tolerance on the material was acceptable for the application).
This aggravates me for several reasons:
- we've got a duplicate bill of material for every part: the MRP bill of material and the drawing bill. This is a significant source of error when you try to maintain parallel BOMs. Inevitably one gets changed without the other, and problems usually follow.
- it adds burden in engineering, because we are responsible for both BOMs. For example, if the planning department finds that we use a lot of 1/4" aluminum plate in certain widths they ask us to create a P/N for plate sheared to width and change the affected BOMs. With both MRP and drawings to change, this is a fair amount of (non value-added) work.
- we've been doing this long enough (on MRP for at least 12 years) that our material cutters aren't even taught how to read the drawing. As a result, if the title block says cut it 7" long, they'll cut it 7" long without regard for the length tolerance or machining allowance. We get an astounding number of requests to change the title block to tell the cutter to cut the part 1/16" too long so the machinist has some material to remove.
- while the RM part numbers may be obvious internally, it can cause problems with outside vendors. An example just came up today. We wanted a bronze-tinted polycarbonate plate with some holes in it, but the part we got was clear. The only material callout was: LEPBRZ1/4. Well I know that is our designation for bronze-tint polycarbonate, and the engineer that designed the part knows it, but obviously it wasn't clear to the vendor. That's a $150 mistake that directly affects our bottom line.
What I'd like to do is call out the material spec on the drawing (e.g. 6061-T6 Aluminum, C1018, Type 304 SS, Bronze-tinted polycarbonate) and let the planning department (or vendor) take ownership of the bill of material. If they're short of flat bar and want to substitute plate, it is their call as long as it meets our material spec.
What does your company do?
Cheers,
Dean
Our company uses an MRP system, and as such every raw material we use has a part number. Our raw material part numbers are significant - e.g. ALF3/8X2 is, you guessed it, aluminum flat bar 3/8" thick by 2" wide.
Our tradition has been to call out the actual RM part number and quantity on the title block. If, for example, we design a part from aluminum and it is 3/8" thick and 2" wide and 7" long, then we would call out ALF3/8X2 (x7.00) in the title block (provided the standard mill tolerance on the material was acceptable for the application).
This aggravates me for several reasons:
- we've got a duplicate bill of material for every part: the MRP bill of material and the drawing bill. This is a significant source of error when you try to maintain parallel BOMs. Inevitably one gets changed without the other, and problems usually follow.
- it adds burden in engineering, because we are responsible for both BOMs. For example, if the planning department finds that we use a lot of 1/4" aluminum plate in certain widths they ask us to create a P/N for plate sheared to width and change the affected BOMs. With both MRP and drawings to change, this is a fair amount of (non value-added) work.
- we've been doing this long enough (on MRP for at least 12 years) that our material cutters aren't even taught how to read the drawing. As a result, if the title block says cut it 7" long, they'll cut it 7" long without regard for the length tolerance or machining allowance. We get an astounding number of requests to change the title block to tell the cutter to cut the part 1/16" too long so the machinist has some material to remove.
- while the RM part numbers may be obvious internally, it can cause problems with outside vendors. An example just came up today. We wanted a bronze-tinted polycarbonate plate with some holes in it, but the part we got was clear. The only material callout was: LEPBRZ1/4. Well I know that is our designation for bronze-tint polycarbonate, and the engineer that designed the part knows it, but obviously it wasn't clear to the vendor. That's a $150 mistake that directly affects our bottom line.
What I'd like to do is call out the material spec on the drawing (e.g. 6061-T6 Aluminum, C1018, Type 304 SS, Bronze-tinted polycarbonate) and let the planning department (or vendor) take ownership of the bill of material. If they're short of flat bar and want to substitute plate, it is their call as long as it meets our material spec.
What does your company do?
Cheers,
Dean
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