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Mixed unit issues?

Gears Phenom Gears Phenom
Gears Phenom

Up until now, our projects have all been in inches, but now we have one that there is a desire to do in metric.

 

I can create a metric model seed file easy enough, but if we don't create metric drawing format files, will we have any (real) issues?  Other than not being able to work on the model, from the drawing (master model setup), due to the unit issue.

 

What about CAM files, will our CNC guys need to use metric CAM files?

 

Will parts export as DXF to scale for the water jet, or will they be 25.4 times too big?

 

How about working with hardware in the reuse library?  will we just get the mixed units warning?

 

Personally, I have concerns about mixing units, and imagine issues like the Mars Climate Orbiter occuring.

-Dave
NX 11 | Teamcenter 11 | Windows 10
6 REPLIES

Re: Mixed unit issues?

Siemens Valued Contributor Siemens Valued Contributor
Siemens Valued Contributor
Hi Dave, are you familiar with the ug_convert_part utility? This post isnt answering your questions directly, but the utility is worth mentioning. More information on the utility is located in the NX documentation.

Re: Mixed unit issues?

Siemens Phenom Siemens Phenom
Siemens Phenom

As long as you don't try to set an Imperial unit Component to be the Work Part while working in context of a Metric unit Assembly, or vice versa, there should be no real problems.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA

Re: Mixed unit issues?

Gears Esteemed Contributor Gears Esteemed Contributor
Gears Esteemed Contributor

On the CAM side, it doesn't matter too much either, BUT...

If your holes, threads, fillets, etc. are metric sizes, you'll need metric size tools to cut them.  I.e. if you form a fillets using a ball mill, and you have a 5mm fillet, if you try to use inch tooling, you may have to surface it (not just planar mill & let the corner radius cut the fillet in one pass).

 

Not sure about the DXF issue

 

Ken

 

 

Ken Akerboom Sr CAx Systems Engr, Moog, Inc.
Production: NX10.0.3.5 MP16/TC11.2
I'd rather be e-steamed than e-diseaseled


Re: Mixed unit issues?

Siemens Legend Siemens Legend
Siemens Legend

You will not have more problems than you have today :-)

 I think(?) that today , there are more Metric users then Imperial users.

 

Regards,

 Tomas

Re: Mixed unit issues?

Pioneer
Pioneer

Dave,

I used mixed units all the time (not by choice).

 

I would try and keep the units of the drawing the same as the model (though you are not forced to). You can use "inch sized sheets" e.g A,B,C,D with "metric" unit models

 

CAM is not a problem if using master model approach. CAM file can be inch and model file (component) metric

 

hardware shouldn't be a problem - will only scale if you are importing geometry (I think). If you're adding hardware as a component, then there is no issue.

 

DXF's typically export with a known set of units in the dxf file, using the header "INSUNITS" 1= inch and 4=mm, so unless exported as zero (unitless) it should always translated in the correct size.

 

The biggest drawback is that you can't have the displayed part and work part (work in context) where the units are different

 

Geoff Donohoo

NX10.0.3.5 & TC 10.1.4.2
Dell T3600 32Gb Ram, Nvidia Quadro 4000
Windows 7

Re: Mixed unit issues?

Experimenter
Experimenter

Speaking as someone whose spent a lot of time working at a firm that mixed units. In general it's not a problem. But I expect you'll wnat dual dimensioning ? E.g. Inches [mm] or mm [inches]

 

If so two caveats

- Be careful regarding tolerance on high precision parts - the displayed decimals and rounding errors can result in a displayed dimension where the inches rounded one way, the metric the other, and as a result the limits displayed on the blueprint are significantly different (as a percentage of the tolerance).

 

Example 25.04 +- 0.04 mm could display as [.986 +- .002] but 25.04 = .98740 not .98800.

 

You have to decide if that discrepancy matters, and adjust the displayed decimals accordingly.

 

- Be careful to turn on the automatic conversion of tolerance and lock it.

 

I suppose those caveats also apply to any other engienering you do - be it in excel or whatever.