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Reasons to use metric
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Gerald J.
Posted 7/23/2014 01:50 (#3981547 - in reply to #3981229)
Subject: RE:Metric lathes



Friend of mine has a couple sturdy Swiss Lathes. One has about 0.5 meter swing and 2 meter bed. The quick change gear box drive change gears can be set for metric or english, but neither has a threading dial. In cutting metric threads both have geared spindles with fast acting brakes and reversing, so once the half nut is closed, it stays closed until the threads are finished. The lead screw is 4 or 8 to the inch. They just don't expect to be able to use a threading dial on metric threads even on a lathe made for metric work. And that's because of the lead screw drive a threading gauge won't work.

The quick change gear box on a pure metric lathe is completely reversed from the drive we are used to. Where we in english threads work in threads per inch, metric are never in threads per mm, but in mm per thread. So a quick change gear box on a completely versatile lathe that will do both metric and fractional has nearly twice the gears and for metric the drive gears change size, while in fractional the driven gears change size or they are mixed and have odd sequences. My friend's big lathe takes a 127 to 50 or 50 to 127 to cut metric in the change gears that didn't all come with it 17th hand.

For my little Atlas 6" lathe I have a hand crank I can mount on the left end of the spindle so I can cut fast threads up to a shoulder without having to open the half nut quickly. That makes for easy backing out for the next pass too.

Gerald J.
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