Design for multi-country manufacture - Metric vs. inch stock 14

[BobVo]

We are a US company which recently merged with a European company. How do we design 'common' products, when we can't but metric stock economically here, and they can't buy US gage, or fractional, stock there?

We certainly aren't the first in this situation. What do other companies do? Any suggestions appreciated.

Thanks.

 

[KENAT]

BobVo, we don't have large run rates for most our stuff so we're probably already being hammered on set up costs when we buy things 5 or 10 at a time.

We don't buy stock material much ourselves, we rely on the machine shops etc to buy their own. That said where the 'stock' dimension remains on the part, such as with sheet metal, it's usually inch sizes (or at least AWG).

Our stuff is a terrible mix, we mostly dimension in inches but have quite a few metric threads. However, every now and then, especially when interfacing with something metric, we have mm drawings.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

 

[telecomguy]

I took a shot at compiling some sheetmetal equivalents. Is this roughly what you were looking for?

Sources for the stock sheet thicknesses were:

http://www.sheetmetalguy.com/sheet_metal_gauge_chart.htm

&

http://www.metricmetal.com/products/crsheets.htm

In today's global economy, I think it's a great idea to design so product can be manufactured from the most economical local materials where permissible. I think I'll start putting a material option on my sheetmetal parts where a precise thickness is not mission critical.

-tg

 

[eromlignod]

Steve wrote:

"Oops, I sound like I'm goading. I'm not. I'm just interested. As I mentioned before, the idea that Volts*Amperes gives the same (W) as N*m/s thrilled me as a kid."

I wasn't trying to say that the Metric System isn't superior in some ways. I'm only saying that it's overrated. The fact that it relates directly to electrical units is nice, but not really that useful.

Power is about the only mechanical/electrical equivalent I ever use. I just remember that there are 1.356 ft-lb/s in a watt.

Now I'll stop hijacking the thread!

Don
Kansas City

 

[BobVo]

Telecomguy,

I agree that, for the future, designing so metric or gage sheet metal can be used is a smart way to go.

Unfortunately, I expect that if we start looking closely at the current designs we will find places where changing the stock thickness will effect fit and function, for example where functional parts sit on top of sheet metal parts. Or where dimensions are to the 'wrong' side of the part.

It appears worse for bar stock, tubing, etc. For instance we make rollers by pressing a cap into tubing. Tubing diameters here and there are not close, so the cap diameter needs to vary to make a reasonable press fit. How do we design these to simplify the future?

So trying to build a present metric designed product in the US looks like it will require a redesign to tweak dimensions to compensate for material thickness in places. - A task that results in two sets of drawings for us and them. Which leads to other issues, like trying to maintain control of the design. (When you ECO a part how do you know if there is another metric or inch drawing of a 'similar' part being used overseas?)

When I originally posted I was hoping that there was someone 'out there' who had been through all this and found a simple solution I was overlooking. We haven't found them yet. ;-)

BobVo

 

[vpl]

Bob

This is a little bit more on track: There's another thread in this same forum that's addressing a (somewhat) similar issue in terms of dimensioning on drawing. You might find it useful: thread404-233255

Patricia Lougheed

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[drawoh]

BobVo,

I don't know anything about European sheet metal gauges. I can see two issues with English sheet metal grades.

[ol]
[li]None of them work out exactly to round inch values.[/li]
[li]There are an awful lot of them, and the thickness increments are small.[/li]
[/ol]

On fabrication drawings, you should not call up the English sheet metal grade. You should call up the thickness, with a tolerance.

For example, you prepare a drawing showing aluminium sheet metal thickness of 2mm±0.2mm. English 12[ ]gauge is 2.06mm thick, placing it well within your tolerances. My Google search for "sheet metal DIN" reveals this table of German sheet metal gauges. DIN 13[ ]gauge is nominally 2mm thick.

Specifying the thickness with a tolerance is the right way to do stuff.

The dimension with tolerance can probably be achieved by sheet metal gauges. Thicker plates are a problem, but you can always make your tolerances sloppier. There is not much difference between 10mm and 3/8" for example. Does it really matter to your design?

The same definitely goes for drills and other tools. I specify holes with zero positional tolerance at MMC, and a sloppy diameter tolerance, e.g. Ø5.0/4.4mm. If an English drill or punch does not fall inside this range, you don't have enough English drills and punches.

JHG

 

[telecomguy]

"When I originally posted I was hoping that there was someone 'out there' who had been through all this and found a simple solution I was overlooking. We haven't found them yet. "

I guess the 'simple' solution would be to machine everything. Then all you have to worry about are varying material properties...

 

[BobVo]

Alas, simple would have been, c. 1975, when the US congress voted to make the US metric, if we had actually followed through. By now metric would be in place, instead of just 'on the books.'

 

[ivymike]

Unless you are brought up in the metric system from your first day in school, you are not capable of thinking in metric

feel free to speak for yourself... just remember that the kids on the longer bus might have had a different experience.

 

[drawoh]

BobVo,

Canada has been officially a metric country since the seventies. When I went to college, we used English units, and the SI (MKS) system. I am comfortable with both. I want nothing to do with CGS units.

Right now, Canadian architects work in metric, and Canadian contractors work in feet and inches.

I am looking at my Machinery's Handbook, Twenty Sixth Edition. They did not separate the drills between numbered, fractional inch, and metric. They listed all the drills, in order of size, all in one table, with diameters in inches and millimeters. I can easily see for example, that if I want to be a tiny, tiny bit above .125"[ ]diameter, I need a Ø3.2mm[ ]drill.

JHG