Design for multi-country manufacture - Metric vs. inch stock
Design for multi-country manufacture - Metric vs. inch stock
(OP)
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.
We certainly aren't the first in this situation. What do other companies do? Any suggestions appreciated.
Thanks.





RE: Design for multi-country manufacture - Metric vs. inch stock
On the fasteners issue, I willl say that metric is probably easier to get in the US than Unified is in most other places.
So it may be you have to look at each category and see if one way or the other has advantages.
I'd be interested in seeing what others post as we have some similar issues and haven't yet forged a clear path forward.
KENAT,
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RE: Design for multi-country manufacture - Metric vs. inch stock
RE: Design for multi-country manufacture - Metric vs. inch stock
RE: Design for multi-country manufacture - Metric vs. inch stock
My boss likes to point out that the U.S. is one of only three countries that isn't metric, and another of those is Libya.
RE: Design for multi-country manufacture - Metric vs. inch stock
So, as has been mentioned, it is no big deal to specify metric equipment for use in America, though it might be a bad idea to use imperial elsewhere.
We don't hate the Metric System in America, we just think it's overrated.
Don
Kansas City
RE: Design for multi-country manufacture - Metric vs. inch stock
eromlignod, I think you may slightly everestimate how 'bilingual' many US engineers are, but certainly agree they're probably more bilingual than anyone except Perhaps Brits, Canadians and maybe a couple other commonwealth places.
I'd almost be more concerned about things like stock material sizes such as scructural tubing, plate etc.
KENAT,
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RE: Design for multi-country manufacture - Metric vs. inch stock
I buy from Parker Steel Company. http://www.metricmetal.com
They have everything metric, no minimum orders, and sales people are very helpful. If you can use short pieces, they sell cut-offs at reduced prices.
Larry
RE: Design for multi-country manufacture - Metric vs. inch stock
RE: Design for multi-country manufacture - Metric vs. inch stock
the automotive industry in europe has put up with such a scheme for years (brakehosecouplings and tapered roller bearins only have become available in metric sizes only in recent years). still engines are sold with a SAE size bell housing flange and trucks with fifth wheels that require an imperial size kingpin....
it all illustrates that in a global world global standards are more then ever needed.
RE: Design for multi-country manufacture - Metric vs. inch stock
A mix of imperial, metric and then a ratio thrown in for good measure.
Does anyone manufacture metric wheel rims?
- Steve
RE: Design for multi-country manufacture - Metric vs. inch stock
RE: Design for multi-country manufacture - Metric vs. inch stock
- Steve
RE: Design for multi-country manufacture - Metric vs. inch stock
Rim thickness = 3.75 mm ± 0.25 mm
Flange thickness = 5.5 mm ± 0.5 mm
Lug hole diameter = 16 mm ± 0.5 mm
I suppose the wheel width from bead seat to bead seat is "noncompliant" at 216 mm, as is the wheel diameter from bead seat to bead seat (436.6 mm).
The solid model, drawing, calculations, dimensional measurement, and testing are all metric, so I think it is safe to call it metric.
RE: Design for multi-country manufacture - Metric vs. inch stock
- Steve
RE: Design for multi-country manufacture - Metric vs. inch stock
Hydraulic fittings - Imperial, O-ring face seal
--Metric fittings are hard to get and $$$ in North America, whereas imperial can be found in EU and to a lesser extent Asia.
Fasteners - Metric
--Watch the differences in head sizes of cap screws between EU, Japan and North America.
--Many of the large components will be metric anyway (transmission, engine, axles, etc.)
Steel - Try to design with thicknesses which can be interchanged with minimal effect. Make sure the design can accept either, and specify either on the drawing.
--This depends on what you can live with, but <0.005" should be OK.
example: 3mm (0.1181") vs. 11 gage (0.1196")
6mm (0.2362") vs. 3 gage (0.2391")
8mm (0.3150") vs. 5/16" (0.3125")
16mm (0.6299") vs. 5/8" (0.625")
Batteries - designed to accommodate either
-- was a pain, but is doable
Tires - Off-road tires aren't an issue, pretty much the same worldwide.
ISZ
RE: Design for multi-country manufacture - Metric vs. inch stock
RE: Design for multi-country manufacture - Metric vs. inch stock
Many say so but they do not know what they are talking about.
Unless you are brought up in the metric system from your first day in school, you are not capable of thinking in metric - you are constantly converting, no mater how hard you try. The Obama administration should make the hard choice:" First day in the new school year - all metric!!!Period. No transition over 5 and 10 years - that is a bunch of crap.They will just nickel and dime it to death. If we fail, we will just raise another generation of young people who are practically illiterate,as far as being able to converse with the rest of the world when it comes to engineering and manufacturing. If you need any proof, look at what happened to the conversion of TV to digital. Years of preparation and than- politics.
Yes, it is a handicap for US manufacturing trying to manufacture to metric dim's because materials like sheet and bar sizes are bought at a premium price and if you buy inch sizes you have to machine it down to the next metric size. So anybody out there rooting for the continuation of our present situation is just secretly trying to keep the inch system in place.
RE: Design for multi-country manufacture - Metric vs. inch stock
I do think that metric (or SI) is overated although the advantages of 1 global system are obvious.
I did junior school in Imperial, senior school in SI, and unversity back in Imperial. No wonder I am mixed up!
RE: Design for multi-country manufacture - Metric vs. inch stock
I can think in metric all I want. When I estimate the metric size of an object, I picture a metric ruler in my head, just like I do with imperial. There is no conversion to it. I know the temperature in my office right now feels about 22C. I can pick up an object and tell you approximately how many kilograms it weighs. What do you want?
...and it's still overrated.
Don
Kansas City
RE: Design for multi-country manufacture - Metric vs. inch stock
RE: Design for multi-country manufacture - Metric vs. inch stock
There are some things in the US that are sold as inch sizes but made to mm. The best example is plastic sheets and films. Even if custom extruded in the US a 1/4 sheet is really a 6mm sheet. I have also seen this with some Al sheet.
I heard the US military switched to metric for new milspec components. Is this true?
(Ever since the 90s most engineering courses are taught in metric with English units only used where they are tricky like slugs in thermodynamics.)
RE: Design for multi-country manufacture - Metric vs. inch stock
However, please note that most so-called "metric" electronic components have pin pitches of 1.27mm or 2.54mm spaced at 7.62mm, 10.16mm and so on at standard conversions of imperial fractions, spindles are 6.35mm and panels have 12.7mm holes and these aren't because they're American, many are Japanese, French, German or Chinese, but it is the "Industry Standard" so we all live with it.
Here in the UK, all the aluminium and brass extrusions we buy are sold in imperial fractional inch dimension for the sections and in multiples of metres for the length! Timber is metric but sheets of ply are so many millimetres thick but still sold in sheets eight by four (feet).
Us old wrinkly's can cope OK, but it's the kids I feel sorry for, they haven't been taught imperial measurments for years now, but all the speed limits are in MPH, road sign distances are in miles with local warnings in yards or fractions of a mile, petrol is sold only in litres, but car mileage is qouted in MPG. Finally, milk and beer is in pints! This is our country's metric policy and I don't see any of this changing much anytime soon!
RE: Design for multi-country manufacture - Metric vs. inch stock
I never heard of a slug in thermodynamics, it was all in lbm or kg. I've seen that in a few old books, but never used in school. I think it went out of style along with dynes, poises, etc. Unlike kg-f, bars, calories, and other non-SI units which I still see.
RE: Design for multi-country manufacture - Metric vs. inch stock
We're international too, and have had many issues just as described. We make small valve parts from spring steel, and so the difference between 4 thou and 0.1mm is significant in terms of bending stiffness. We've standardized metric as we see this as the long term global direction.
RE: Design for multi-country manufacture - Metric vs. inch stock
So you use metric stock..
How do you address dimensioning the parts? Do you dimension them in all metric, and shops in the US live with that? Or dual dimension the prints? Or...
What about punched hole sizes? Do you call for standard metric hole diameters? What do US companies do to punch those hole sizes? (Buy metric punches?) Or...
Bob
RE: Design for multi-country manufacture - Metric vs. inch stock
"lbm" are strictly bush-league. Try putting lbm in a formula as simple as F = ma and you'll see what I mean. The imperial unit of mass is slugs, force is in pounds.
1 lb = 1 slug-ft/s^2
As long as you use slugs for mass you can use all the same simple formulas that you use in metric.
Don
RE: Design for multi-country manufacture - Metric vs. inch stock
The US used to be the leader in machine tools and wrote the book on many standards like tapers, CNC, machine building and design etc. etc.. Unfortunately that is no longer true. Many new Standards being written for ISO seem to have very little US input or am I just plain wrong on this?
It looks to me like most are an exact copy of the German DIN Standard.
Neglecting our manufacturing sector has changed our society to one more resembling some in the Near East or Mediterranean area where the preferred way of making money is not by engineering and making a product but by buying and selling. Nothing against it - it's the way capitalism works.
However, the results of a free wheeling and unregulated capitalistic society are now coming to haunt us. I am by no means promoting socialism but something needs to be in place to assure that critical industries and skills are still available for future generations.
We have to make sure that one thing is kept under control, and that one thing is "Greed".
We do not need politicians who forever are looking to make sure they do not offend anybody. We need leaders in Washington who can lead and make decisions that are good for the future of the country, even if these decisions are sometimes not very popular.
Otherwise we might es well be governed by a bunch of bureaucrats who than make decisions by plebiscite.
One of these decisions should be to make a final and clear cut to convert this country to metric asap.
And "yes" the US Army is metric - has been for a long time. It was not easy to teach soldiers how to direct Artillery fire and call in adjustments by meters when they where all thinking in feet. But that was in the seventies and now we have GPS.
RE: Design for multi-country manufacture - Metric vs. inch stock
Katmar Software
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RE: Design for multi-country manufacture - Metric vs. inch stock
Then they gave us a consistent unit set. Brilliant, absolutely brilliant. I was so thrilled that power and energy from electrical systems was interchangeable with power and energy from mechanical systems.
- Steve
RE: Design for multi-country manufacture - Metric vs. inch stock
m=w/g
F=ma=wa/g
In the English system, you can ignore slugs and just substitute w/g. Now, you can convert units between inches, feet and millimters to your heart's content, as long as you do not screw up your arithmetic. Since the Newton is a unit derived from meters and seconds, you have to be disciplined about using meters and seconds as your units in SI calculations.
Don't forget that the SI system is mks (meters, kilograms, seconds). Lots of metric types still use cgs (centimeters, grams, seconds).
In the English system, slugs are the derived unit. This is an excellent reason not to use slugs.
RE: Design for multi-country manufacture - Metric vs. inch stock
KENAT,
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RE: Design for multi-country manufacture - Metric vs. inch stock
Knowing that BobVo's question has been answered, and that this thread has gone off on a tangent about units and a further tangent about the word "slugs"...
I have to add, that beer is a good way to get rid of slugs. Whether you drink it, or they do.
Patricia Lougheed
Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.
RE: Design for multi-country manufacture - Metric vs. inch stock
While perhaps not quite as common as inch series, common mm size tools are I believe fairly readily available.
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?
RE: Design for multi-country manufacture - Metric vs. inch stock
Regards,
Mike
RE: Design for multi-country manufacture - Metric vs. inch stock
Using pounds-mass is as stupid as using kilogram-force (which you do see sometimes). As long as you use slugs for mass you can use all the same, simple mechanics formulas as for metric.
How much force does it take to accelerate a 3-slug mass at 15 ft/s/s? Simple:
F = ma = (3 slugs)(15 ft/s^2) = 45 lbs
What torque results from 20 lbs exerted on a 3-ft lever arm?
T = Fr = (20 lbs)(3 ft) = 60 lb-ft
How much work is exerted when you push on a block with 5 lbs over a distance of 10 ft?
W = Fs = (5 lbs)(10 ft) = 50 ft-lbs
Force is in pounds, torque is in pound-feet, energy is in foot-pounds. In all of these units pounds are force, not mass. This is how these quantities are expressed in the engineering world. When you look at spec. sheets and standard tables, this is what you find, not "pounds and poundals" (how confusing). Pounds are force.
Don
RE: Design for multi-country manufacture - Metric vs. inch stock
Pounds and Kilograms are traditional units, frequently, however improperly, used for mass and force respectively, as you noted. Slugs and Newtons are derived from force equations involving the traditional units. If you write an equation with slugs or Newtons, you have to convert all your units into whatever units were used to derive the slugs and Newtons. If your equations use pounds and kilograms, you can use whatever units you want, although you have to be consistent.
I have never seen a mass scale calibrated in slugs. On a good day, force scales are not calibrated in kilograms and grams.
In English units, I almost always use inches as my length units. I am pretty certain this rules out the use of slugs, which I believe are derived using feet. I cannot be bothered to look this up.
I must admit that when I am doing calculations in metric, methodically converting all units to the SI MKS is trivial.
RE: Design for multi-country manufacture - Metric vs. inch stock
We quoted metricmetal.com on some sheet stock.. but found they want $247 for an aluminum sheet similar to a .060 sheet our vendor pays $55 for. And $690 for a metric sheet similar to a 16 gage sheet our vendor pays $138 for. At these prices 130 sheets per week of metric sheet metal would obviously drive our costs through the roof.
I'll discuss metic punches with our vendors... (but fear they might be forced to raise part prices to cover the cost of the additional metric tooling.)
Also, as some of our low priced suppliers don't have state of the art presses which can store many more punches than needed, press setup times will increase, as the 'normal' tools in the press will never be the ones we need.
BobVo
RE: Design for multi-country manufacture - Metric vs. inch stock
So how do you unite the mechanical and electrical systems. What are the equivalent imperial units for current and voltage that allow seamless working between the two domains?
- Steve
RE: Design for multi-country manufacture - Metric vs. inch stock
- Steve
RE: Design for multi-country manufacture - Metric vs. inch stock
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,
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RE: Design for multi-country manufacture - Metric vs. inch stock
Sources for the stock sheet thicknesses were:
http:/
& 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
RE: Design for multi-country manufacture - Metric vs. inch stock
"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
RE: Design for multi-country manufacture - Metric vs. inch stock
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
RE: Design for multi-country manufacture - Metric vs. inch stock
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: Significant Figures On Dimensioned Drawing When Converting Units
Patricia Lougheed
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RE: Design for multi-country manufacture - Metric vs. inch stock
I don't know anything about European sheet metal gauges. I can see two issues with English sheet metal grades.
- None of them work out exactly to round inch values.
- There are an awful lot of them, and the thickness increments are small.
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.
RE: Design for multi-country manufacture - Metric vs. inch stock
I guess the 'simple' solution would be to machine everything. Then all you have to worry about are varying material properties...
RE: Design for multi-country manufacture - Metric vs. inch stock
RE: Design for multi-country manufacture - Metric vs. inch stock
feel free to speak for yourself... just remember that the kids on the longer bus might have had a different experience.
RE: Design for multi-country manufacture - Metric vs. inch stock
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.