I'm applying for some funds to set up a small makerlab-type metalshop in my department (American research university, although I should note that I'm in the social sciences). My plan is to get a CNC mill and lathe along with some 3D printers for rapid prototyping of equipment.

My question is whether to get metric or imperial CNCs. Yes, it's easy to flip the display controllers between metric and imperial, but the gearing of the mill itself is usually based on a metric or imperial leadscrew, so that 1 turn of the handwheel turns a certain metric/imperial based distance.

I checked the other metalshops at my university and they are use imperial-unit Bridgeport mills and lathes. I myself grew up in a metric country (i.e., somewhere other than the US, Liberia, and Burma) and so find this incredibly backwards.

Is there any good reason to go with imperial-based lathes and mills -- except for the cost of finding a good metric one?

Note 1: For lathes, it is relatively easy to change the gearing for metric, so this is not as much of an issue as it is for mills where the X, Y, and Z leadscrews and indicators would need to be swapped out. Not to mention the difficulty in sourcing metric borers and bits...

  • We really need a Mech E stack exchange, or a maker see. – RoboKaren Jul 12 '14 at 16:20
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    This seems to be a question about metalworking, rather than a question about academia. – David Richerby Jul 12 '14 at 16:36
  • There's no mech e SE and I'm curious whether metalshops at other universities in the USA also only use imperial or if we're an anomaly. – RoboKaren Jul 12 '14 at 16:39
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    A private metal shop can do what the heck it likes, but a university is supposed to promote knowledge and engage in best standards. – RoboKaren Jul 12 '14 at 16:41
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    The funding agency may have an opinion. Beyond that there is no "right" answer. You could ask the people in charge of the other shops on campus what their reasons were. – dmckee --- ex-moderator kitten Jul 12 '14 at 16:49

The decision will be decided based on where, or in what, you think the resulting parts will be used. Since you are in the US, going for the imperial would make most sense.If you start machining metric based parts you will soon find that you may have problems adding off the shelf parts. I think the sound way forward is to figure out if you will depend on parts from elsewhere and to what extent these will likely be metric or imperial. Being able to switch will solve some issues but as you state, if there are mechanical differences in the machinery, you may end up with less accurate parts when switching to whatever system the machinery was not made for.

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