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.

Sunday, 21 February 2016

Adventures with a Watchmakers Lathe - Part 1.

NOS Balance staffs for a size
16 watch - these for a Moeris
are particularly simple ones!

As with all pictures here click on
 the image for a larger view
There are a few watchmaking repairs that can only be done with a lathe and similar tools, the most critical being the manufacture of replacement balance staffs. Whilst replacement staffs are available from New Old Stock (NOS) for most watches by Waltham and several of the Swiss makers such as Cyma/Tavannes and Revue (that is one reason I deal in those makes) it is becoming increasingly hard to find them and prices are correspondingly rising, also NOS staffs are not available for any English watch made pre WWII.

For sometime I have been contemplating buying the necessary equipment and investing a considerable amount of time learning how to use it - several weeks full time I suspect before usable staffs are produced -  I haven't used a lathe since my apprenticeship days which was rather a long time ago and that lathe was about 6 foot long.

Having bitten the bullet and decided to do it I have finally managed to buy a second hand lathe and whilst I am closed for business awaiting the new financial year and for the supply of watches to pick up I will be writing a few blog entries to chart progress and to describe key aspects of the lathes use.

The first problem is the cost of a lathe, a new fairly comprehensive (but not complete!) set up by Bergeon, a premium supplier of quality watch and jewellers tools, is currently £27,594 (plus cutting tools and other bits and pieces) so that is clearly out of the question, even a "budget" watchmakers lathe by "Star" to a basic specification and with no motor is £2,874 and would require quite a few extras to make is usable for making staffs.

My Pultra 10 Lathe after
a days worth of restoration.

So clearly second hand was the way to go, after several failed attempts I was very fortunate to acquire an excellent English lathe by Pultra probably made in the early 1950s and with a very good specification. I was particularly fortunate in that some one tried to "snipe" me with a bid in the last 10 seconds of the eBay auction and I won by 12 pence!

A couple of the collet chucks (more of which in a later post) need replacing at between £20 and £45 each new (depending on size) or £10 - £15 used and I may want a few more, but apart from that it has all of the pieces necessary, except a motor which the seller has yet to auction.

However I have decided to go with a new electronically controlled motor which is on order, it is not designed for this type of lathe so will need some work to mount it and the lathe onto a base board and to connect them up.

One interesting feature of watchmaking lathes in general is that they are operated very much like a wood turners lathe with the cutting tool hand held, this close up shows the tool rest (not in position in the picture - in use it would be closer to the centre line). This particular one is a premium "tip over" type which can be folded back to allow access to the work for measuring etc. and then tipped forward, back into position without having to reset its position.

The whole lathe is 10.5 inches long and the tool rest only an inch long so this is pretty small precision engineering!

It was missing a few, mainly non essential but nice to have things, most of which I have now sourced and hopefully they will all be here in a week or so.

So far the total cost is about £1.2k but small compared to £28k for a Bergeon!

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