Sunday, 28 February 2016

Adventures with a Watchmakers Lathe - Part 2.

A week has gone by since my first post on this subject and the lathe is now operational.

The new motor, when it finally arrived, turned out to have tapped mounting holes underneath as well those at attaching it to the mounting plate for the Unimat lathe it was intended for, so mounting the motor was easier than expected.

The original mounting plate was retained to support the control box but underwent major surgery to get it out of the way.

The motor is on a 4 sided carrier of angled aluminium I had available and runs on two rails of the same. Holes are at 1” centres on the carrier and ¾” centres on the rails so there is plenty of room for adjustment fore and aft without having to change the height of the lathe. The adjustment is required so that the belt can be moved to each of the three wheels on the lathe, giving different speeds, to take up slack from stretch and to compensate for any errors in making the belt which is plastic, cut to length and then the ends melted and pressed together. It is important not to have the belt too tight which can damage bearings, too slack and the belt will slip.

The best arrangement is for the belt to slip only if you are too heavy handed with the lathe tool, protecting the motor and hopefully the tool and work piece.

I didn’t care for having the speed control changed every time it was switched off and also thought it would be a good idea to be able to turn it off in a hurry so I put added on/off switch with an emergency off button.

The motor gives all of the power (110W continuous 100 – 5,000 rpm) I will ever need (and more). I just need to pain the original mounting plate, get a better mains cable and some clamps to avoid pulling the cable from the switch box and its done.

8mm WW standard Collet
The second picture shows the lathe with a four jaw traditional lathe chuck and a cross-slide tool carrier. Both of these features are useful but the vast majority of work will be done with a hand held "graver" cutting tool and using an 8mm Collet (or "wire")chuck in the configuration of the first picture.

I had though of writing a piece on the benefits of the Collet chuck in watchmaking but it would have been a bit technical and I found this article on Wikipedia that covers the ground.

The following table is taken from that article:

"The collet's advantages over other chucks is that it combines all of the following traits into one chuck, a valuable combination for repetitive work:"
-ColletScroll chuckIndependent-jaw chuck
1. Fast chucking (unclamp one part, switch to a new part, re-clamp)ReliablyReliablyGenerally not
2. Self centeringReliablyReliablyNever
3. Strong clampingReliablyUsuallyReliably
4. Resistance against being jarred loose (untightened)ReliablyTo varying extentsUsually
5. Precise centering (run-out less than 0.005 in (0.13 mm) TIR and usually less than 0.001 in (0.025 mm))ReliablyNot reliablyReliably (but requires time and skill)

Click on "Lathes" under labels to the right of the page for other articles in the series.

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