Converting dimensions from Metric to English - ISO or other issue?

A lot of our parts that we cut on a laser are simple ID/OD "donuts". As such we often modify a generic program rather than importing a DXF as we're having a hard time getting the layers standardized so we don't have to strip out a bunch of stuff. I am reasonably certain that the shop is converting Metric dims to English for these cases (hopefully in anything more complicated that maybe has notches or cutouts they aren't). Does this present any inherent quality issues; more from an ISO viewpoint that we might be breaking a rule or standard. Just curious. To me, I just wonder what they are really saving. At the very least they've created an opportunity to introduce error (not just in typing it in vs. DXF import but also in the conversion).

Any input here?

PS - getting ready to leave for a 3-4 day weekend; I'm among the lucky who don't have to answer email away from work!

Thanks,
The Dude

Well, if your operation is ISO-certified, it seems to me you likely have a written procedure for conversion of manufacturing data from English to metric and vice versa. If you do not have such, then an ISO audit might turn this up as a finding, unless it's buried so deep in the method of work that it is non-obvious. If the machine you are using for the actual processing is set up to run in English dimensions, I would be doing exactly that task of conversion of mm dims to inch dims.

I don't think you are breaking any rules as seen from the external world's standpoint. If you do have some motivation to create a controlled process for conversion of dimensions, I would recommend just looking at the specs for the machines in use and the tolerances you are quoting, and make sure your conversion process uses enough significant digits to catch all the error contributions. That said, it may be that running a machine controller in metric units may gain a small increase in resolution, based on the digitization process between encoders and controller interpretation.

Don't forget that new batteries for the calculator every 3 months should be in the ISO process.;-)

If you don't have a written procedure for that in your ISO paperwork the auditor could suggest this as an improvement but they don't have a leg to stand on as far as making a deal out of it in my experience.

ISO is more about saying what you'll do and doing what you say - so if you don't say you don't have to do I wasn't here when we implemented ISO but metric to imperial conversions has never come up in my dealings with the auditor and we were just recertified a month ago.

The Dude said:

A lot of our parts that we cut on a laser are simple ID/OD "donuts". As such we often modify a generic program rather than importing a DXF as we're having a hard time getting the layers standardized so we don't have to strip out a bunch of stuff. I am reasonably certain that the shop is converting Metric dims to English for these cases (hopefully in anything more complicated that maybe has notches or cutouts they aren't). Does this present any inherent quality issues; more from an ISO viewpoint that we might be breaking a rule or standard. Just curious. To me, I just wonder what they are really saving. At the very least they've created an opportunity to introduce error (not just in typing it in vs. DXF import but also in the conversion).

Any input here?

PS - getting ready to leave for a 3-4 day weekend; I'm among the lucky who don't have to answer email away from work!

Thanks,
The Dude

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Ahh, Would that be American English, or England English? Imperial would be easier to talk about. Are the English still using barley corns, and stones?

short tons and long tons? And who uses Imperial gallons? The English? ;-)

Hey thanks all. In my haste to get out the door, I didn't explain that we aren't ISO certified yet. Sounds like we can plan for this though in our eventual certification.

The Dude

CalG said:

Ahh, Would that be American English, or England English? Imperial would be easier to talk about. Are the English still using barley corns, and stones?

short tons and long tons? And who uses Imperial gallons? The English? ;-)

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In the US we speak North American English and we use the English system of measurement. If you don't want to call it English, then call it the Inch system. But it is definitely NOT "Imperial" and has never been called that except in a few places where they accept Canadian money...

Oldwrench said:

In the US we speak North American English and we use the English system of measurement. If you don't want to call it English, then call it the Inch system. But it is definitely NOT "Imperial" and has never been called that except in a few places where they accept Canadian money...

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In Canada we typically call it Imperial, or "standard" (I assume because at one point it was the standard)

I'm interested as to what other countries call it...

capital7 said:

In Canada we typically call it Imperial, or "standard" (I assume because at one point it was the standard)

I'm interested as to what other countries call it...

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Near as I can tell (not 100% conclusive, and I only looked it up as a result of this thread), is that here in the US it's called "United States Customary Units". I just don't ever remember it being referred to as such; even in late 70's early 80's engineering classes but it's possible I slept through it (as I did with a few other classes).

The Dude

Hazzert said:

If you don't have a written procedure for that in your ISO paperwork the auditor could suggest this as an improvement but they don't have a leg to stand on as far as making a deal out of it in my experience.

ISO is more about saying what you'll do and doing what you say - so if you don't say you don't have to do I wasn't here when we implemented ISO but metric to imperial conversions has never come up in my dealings with the auditor and we were just recertified a month ago.

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The only thing I can think of related to metric/inch and ISO is exactly what he said, if you don't specify it, you don't have to document or do it a certain way. I would think however, that if a customer supplied you with a metric drawing I imagine they would want a CofC and/or inspection reports in metric. Now, if they are reports generated by typing data into a spreadsheet or whatever, no big deal, just convert them and enter the info. If it is a CMM report that is auto-generated (ours spits out a pdf), you may have to change a setting to make it output the appropriate unit.

What you want to document is how you keep from screwing it up, ISO be damned. Years ago I raided the shop on a weekend and grabbed every scrap of paper in the shop and locked it in my office. Then I issued new drawings for every part, and collected them with all the markups once the parts were made, applying all the changes back to the drawing files. I did this because I kept issuing revised drawings and getting the same parts as the old ones!