Handling Metric and Imperial Versions of the Same Part
Handling Metric and Imperial Versions of the Same Part
(OP)
Hi All,
A client has a few sheet metal parts that are each going to be made by two different suppliers. One supplier is in North America and prefers to work with Imperial stock material thicknesses and the other supplier is abroad and prefers metric stock thicknesses.
The suppliers each want DXF files of the nominal geometry. I have been told that the nominal material thickness affects things like bend radii, and thus affects certain dimensions on both the flat pattern and the final part.
The client would rather not have to create and manage two different drawings and two different DXF files for each part. Any ideas on how this type of situation is commonly dealt with?
A client has a few sheet metal parts that are each going to be made by two different suppliers. One supplier is in North America and prefers to work with Imperial stock material thicknesses and the other supplier is abroad and prefers metric stock thicknesses.
The suppliers each want DXF files of the nominal geometry. I have been told that the nominal material thickness affects things like bend radii, and thus affects certain dimensions on both the flat pattern and the final part.
The client would rather not have to create and manage two different drawings and two different DXF files for each part. Any ideas on how this type of situation is commonly dealt with?
Evan Janeshewski
Axymetrix Quality Engineering Inc.
www.axymetrix.ca





RE: Handling Metric and Imperial Versions of the Same Part
If you are using a 3D CAD package like SolidWorks, send them the CAD files. Sheet metal fabricators find these useful. Converting from metric and English is as simple as pulling down the Units button in SolidWorks. I am sure the other packages are similar. Our vendor does this with our metric drawings.
A DXF file can be converted, by the supplier, from metric to English by scaling everything by 10/254. He will have to fix the tolerances and the fonts.
Your client should manage one set of drawings, in the original set of units, with the original tolerances.
Don't specify metal stock. Call up thicknesses and tolerances. Make sure your thicknesses overlap metric and English stock. 2mm sheet aluminium is very close to 12 gauge aluminium sheet, for example.
RE: Handling Metric and Imperial Versions of the Same Part
As to bend allowances, flat pattern... often best to leave it to the shop to specify this and stick with what ASME Y14.5 says in section 1.4 about detailing the finished part.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Handling Metric and Imperial Versions of the Same Part
Thank you for the input, that helps.
I investigated the issue further, and it turns out that the issue is mostly to do with who is going to do the scaling of the DXF file. I had forgotten that DXF is a "unitless" format. I agree with drawoh that any required scaling should be the vendor's responsibility.
Would you recommend using a different neutral file format such as STEP, that encodes the intended units? Is this generally better?
Evan Janeshewski
Axymetrix Quality Engineering Inc.
www.axymetrix.ca
RE: Handling Metric and Imperial Versions of the Same Part
Yes. Though some vendors complain they can't read them.
RE: Handling Metric and Imperial Versions of the Same Part
"Art without engineering is dreaming; Engineering without art is calculating."

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RE: Handling Metric and Imperial Versions of the Same Part
If the drawing says what units it is in, then I don't see the big deal. Don't get me wrong, I've had a few moron facilities guys that couldn't work out why our tool footprints came through a factor of 25.4 off but well, you can't fix stupid.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Handling Metric and Imperial Versions of the Same Part
A DXF copy of your fabrication drawing shows intelligent dimensions, which ought to update correctly when you re-scale everything.
I am surprised your vendor does not want your 3D CAD files. SolidWorks sheet metal is intelligent. I am sure ProE/CREO and Inventor are too. Generating a flat layout requires some skill and knowledge that the fabricator ought to have. Let them do it.
I assume you can scale a STEP file, but I have never done it, and I have no interest in doing it.
At some point, if your fabricator has high end CAD software, he can model the part based on your drawing, reproduce your drawing and your units, check his drawing off of yours, and then change units. I can see no use for an unintelligent 3D CAD file, unless your part is hard to visualize.
RE: Handling Metric and Imperial Versions of the Same Part
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Ben Loosli
RE: Handling Metric and Imperial Versions of the Same Part
Send them the drawing as PDF with dimensions so they know the real size of the part. It's too easy to screw up without the info.
Chris
SolidWorks 10 SP5.0
ctopher's home
SolidWorks Legion
RE: Handling Metric and Imperial Versions of the Same Part
This is not even a can, but rather 55 gallon barrel of worms, especially if by DXF you mean "flat pattern".
One flat pattern will never work with 2 materal thicknesses, unless the tolerances for final product are +- .100"/2.5mm.
And it always will be your fault, because you supplied "wrong" flat pattern.
The best you can do, is to supply drawing of final, formed part.
The drawing of the flat should be concidered "reference", with note like "Generated using arbitrary values of thikness so-and-so, bend radius so-and-so, K-factor so-and-so. It is vendors responsibility to generate flat pattern"
Sorry, but IMHO there is no good way out of your situation.
RE: Handling Metric and Imperial Versions of the Same Part
Step file should also be useful, provided your suppliers have the required software to read/use them.
NX 7.5
Teamcenter 8
RE: Handling Metric and Imperial Versions of the Same Part
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Handling Metric and Imperial Versions of the Same Part
Along with STEP, Parasolid is a format commonly used by many / most CAD packages now.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com