Dual Drawings vs. Dual Dimensions?
Dual Drawings vs. Dual Dimensions?
(OP)
I work for a global company with 90% of our part design coming from Europe. As a result the European group controls the drawings. When I present these drawings to local vendors in the US the qoutes come back very high because of the metric shapes (square, round & rectangular tubes, mm size plate, etc.) Of course I can have the parts fabricated from inch size material and they will work just fine. The problem is that if I go to a "close" inch size the dimensions on the drawings are all off a little. Using dual dimensions helps with the the finished part but not the bill of material. I was thinking of having a 2 page drawing with metric on page 1 and imperial on page 2. I would also propose an alternate bill of material to cover the imperial dimensioned page. Has anyone ever done something like this or tried. Did it work? Thank you for any input.





RE: Dual Drawings vs. Dual Dimensions?
KENAT,
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RE: Dual Drawings vs. Dual Dimensions?
If you start re-dimensioning everything to take into account the fact it will be made from imperial stock you are opening up a whole can of worms.
RE: Dual Drawings vs. Dual Dimensions?
The tolerance cannot be relaxed to that extent.
RE: Dual Drawings vs. Dual Dimensions?
Which means having the same part number for each is a bad idea.
I suppose you could still have a common drawing, with different "-" numbers for the metric or inch parts but this might be messy.
You would have to have different BOMs as you say for metric or inch.
At a previous employer we'd sometimes re-design American designed equipment to use metric standard sizes etc. It was never as simple as it sounds.
Unless you have fairly high run-rates it may cost more to create the inch equivalent than the extra cost of the metric material.
In some instances dimensioning at the assy level and just calling up stock can accomodate this but that has its own issues.
KENAT,
Have you reminded yourself of FAQ731-376: Eng-Tips.com Forum Policies recently, or taken a look at posting policies: http://eng-tips.com/market.cfm?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Dual Drawings vs. Dual Dimensions?
RE: Dual Drawings vs. Dual Dimensions?
RE: Dual Drawings vs. Dual Dimensions?
How much money will it cost to do these extra drawings, is it worth it?
KENAT,
Have you reminded yourself of FAQ731-376: Eng-Tips.com Forum Policies recently, or taken a look at posting policies: http://eng-tips.com/market.cfm?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Dual Drawings vs. Dual Dimensions?
I think design change rules apply here. Any change to form, fit or function or any combination of the above, requires a new part number. Any two parts with the same part number must function identically in the same application.
If you can open up tolerances enough to allow inch or metric material, go ahead. If you need to re-design your assembly to use inch components, they must have separate part numbers.
It is possible that at the assembly level, the inch system is interchangable with the metric one. Your maintainance people still need to know what components were used. You could tabulate the assembly drawing.
Maintaining two versions of an assembly at the same time is more complicated than revising the assembly, changing metric components to inch components. The assembly drawing and/or parts list revision letters allow you to distinguish between inch and metric, assuming that the metric design is not manufactured any more.
Is there any chance you can contain the inch modifications to a functionally identical sub-assembly?
RE: Dual Drawings vs. Dual Dimensions?
RE: Dual Drawings vs. Dual Dimensions?
RE: Dual Drawings vs. Dual Dimensions?
HOWEVER - BE CAREFULL. We have seen some drawings over the years shrink or grow as people converted back and forth between Imperial and Metric. The conversion is NEVER exact.
RE: Dual Drawings vs. Dual Dimensions?
First mistake: Change all DIN print size to nearest print size used by the company - they have their own sizes.
Result: Once the company print sizes were put on the company computer file (only the symbol for the company print size was listed and filed) the system mixed and listed our existing US prints with the DIN prints since all had the same company size listed.
End result: Nobody could find a print unless you knew whether it was a German or US part. Now that the DIN sizes were all filed in DIN cabinets by DIN size (A0, A1, A2, A3 etc) you had to guess what US size was closest to the DIN size. You always needed to look in separate file cabinets.
Than they employed a draftsman to re-draw all German part prints in inches. Total disaster. Not only did the lack of know how and understanding of both systems (Tolerances in DIN or ISO) turn out to be a big hurdle, but after retiring the original German print and issuing new prints among others to "receiving inspection" another problem occurred.
We had hundreds of vendors in Europe and all of these had our original print on file (and parts in stock). Now when we received parts they were checked against the new English prints and often returned to the vendor because of a difference in tolerances or material spec's. What a mess!
Part two.
Each part had a manufacturing route in German.
First mistake: 1300 routes, average 20 operations ea. Decision was made by top management to use computer translations from a reputable translating company. The asked whether we wanted a straight computer translation or a manual translation. It was decided to use a straight computer translation. Cost - over $10000.00 vs. a price into the millions for a manual translation (the translating co. would have to send a team to Germany and the to the US company to learn all the terminology specific to the product line).
End result: Nothing but garbage.
Part three.
Building tools and dies to German prints.
Since I was the foreman of the tool room I was able to influence that part (after some flack).
I decided to build all the tooling and gages as they were drawn in metric and to DIN. From our company in Germany I ordered a computer printout listing all tooling and DIN print sizes. Had the DIN tool print cabinets separated from the mixed up part prints.
As to actually building the tools.
At first we tried to save money by keeping the material sizes listed in metric to the nearest inch size. The idea was to cut down on cost for milling inch sizes down to metric dim's. Sounded OK at first but we soon found out different. Many of these tools were very complicated multi-station CNC-tools on top of comlicated milling-, drilling-. grinding and other fixtures and gages. When the tool & die makers started working with metric print specifications and inch material they soon found themselves in deep trouble. It proved very difficult to work in both systems and finally we decided to build the tool as drawn in metric and start cutting our inch material down to the correct metric size (in time we bought more and more metric material)
The lesson learned here: DO NOT MIX THE TWO SYSTEMS!.
I had our German company send me some DIN - books from "Beuth" so we could look up all the DIN standards.
The problem with translating manufacturing routes was finally solved (after suggestions of using someones German speaking grandmother). I insisted (finally finding an open ear) on a line for line manual translation. We found a very intelligent bilingual young lady who would spend hours with me and keeping detailed notes. After some time she got better an better and all I needed to do was proof read her translations. It took a few years, but the job got done right and no parts were scrapped because of errors in translating.
Final analysis: Don't ever mix the two systems. Make your prints either completely in metric or in inches.
If you get a metric print, leave it. If you try to change part of it you are already asking for trouble.
Now that all NEW parts are in metric (we are still fighting this) we decided that all tooling for metric parts would be in metric. This is very important.
P.s.: I can see some "very simple" parts or tooling being made using solid inch material to save cost. Nothing complicated.
Nordern - I hope this helps you in you decision.
RE: Dual Drawings vs. Dual Dimensions?
RE: Dual Drawings vs. Dual Dimensions?