Precision lathes

[david]

The VECTOR  LATHE is a Sincere lathe (made in China) put into a pretty wooden box and remarketed from Germany.  Due to the magic of designer label mindset,  an assumption is made that because it is sold from Germany, it is also made in Germany.  When all is said and done the Vector lathe is a Sincere lathe with a jacked up price.   Both the Sincere and the Vector lathes are good quality watchmaker lathes and are adequate machines to make staffs, pivots, screws and other small watch size parts.

What is often missed in the discussion of small lathes is the use of a cone bearing vs a ball ball bearing headstock.  No matter what designer label and regardless of the price of a lathe, a cone bearing headstock has a precision limitation of about .0002 (two ten thousandths) of an inch of spindle runout. You can only get so much precision from a cone bearing headstock. The more you tighten the spindle of a cone bearing lathe the less spindle  runout and more precision  you get. The problem is, as you tighten the spindle nut you reach a point where the spindle begins generating heat from friction and  can destroy the lathe. 

A precision instrument size lathe like a DERBYSHIRE or a LEVIN uses ultra precision ball bearings and can hold a spindle runout to about 50 millionths of an inch.  The extra precision can eliminate secondary grinding operations and the risk of losing concentricity  due to removing the turned part from the lathe.

david

[JohnR725]

18 hours ago, david said:

What is often missed in the discussion of small lathes is the use of a cone bearing vs a ball ball bearing headstock.  No matter what designer label and regardless of the price of a lathe, a cone bearing headstock has a precision limitation of about .0002 (two ten thousandths) of an inch of spindle runout. You can only get so much precision from a cone bearing headstock. The more you tighten the spindle of a cone bearing lathe the less spindle  runout and more precision  you get. The problem is, as you tighten the spindle nut you reach a point where the spindle begins generating heat from friction and  can destroy the lathe. 

As nice as that paragraph is? Yes it's all true but most watchmakers lathes use cone bearings. Then are we going to get nitpicky about whether there are hard or soft bearing? Or lump all those bearings together? The basic standard watchmakers Lathe that's been in existence for the last Very long time quite a few years uses cone bearings. Then there's thousands millions I don't know how many people there been using those since the beginning of time no one told them they had crappy lathes and they're still making beautiful staffs doing all kinds a beautiful machining without precision ball bearings.

On 3/5/2022 at 4:49 PM, Angrybear said:

Im spending a lot of time modifying watch cases at the moment, and I would really like the ability to be able to make small adjustments here and there. For example I have a case I would like to take 0.5mm off the opening to accept a larger dial, and another I would like to change the profile of the bezel, one I would like to adjust the case back. None of the jobs I want to do really require removing a lot of material, I certainly don't intend on turning a case from scratch.

One of the problems with moving discussions and combining them in with other discussions is questions get lost perhaps? So did we come up with a good idea for this question that was originally asked?

 

 

 

[nickelsilver]

18 hours ago, david said:

 

What is often missed in the discussion of small lathes is the use of a cone bearing vs a ball ball bearing headstock.  No matter what designer label and regardless of the price of a lathe, a cone bearing headstock has a precision limitation of about .0002 (two ten thousandths) of an inch of spindle runout. You can only get so much precision from a cone bearing headstock. The more you tighten the spindle of a cone bearing lathe the less spindle  runout and more precision  you get. The problem is, as you tighten the spindle nut you reach a point where the spindle begins generating heat from friction and  can destroy the lathe. 

 

Sorry to pile on, but there are advantages and disadvantages to both plain and rolling bearings. With a plain bearing, "runout" can be brought to levels where specialized equipment and temp control etc. are necessary to detect it. Since the spindle itself is the moving part of its bearing, and it will invariably be finish ground internally in its own stationary bearings, the precision is incredible. There does always have to be some freedom, a space for the oil. In use, when well adjusted, the oil forms a film around the spindle that is effectively immoveable, while eliminating metal to metal contact. Plain bearing machines with 100s of thousands of hours of use out of watch factories are often in surprisingly good and accurate condition. Some very sought after precision grinding machine use plain bearings, usually bronze and hand scraped to fit, because of the superior surface finish they can achieve.

 

But, a plain bearing machine won't hit peak performance until up to a certain temperature. Derek Pratt used to use stick-on thermometers on the heads of certain plain bearing machines so that he could use them at a consistent temp when doing really tricky work. A ball bearing machine is always ready to go, will have zero spindle play at any temperature or speed, don't necessarily need daily lubrication (often they are lubricated to run for at least 5 years without being touched, and don't tend to sling an oil film down the front of your shirt, which is one of the nicest features! I do love my ball bearing watchmaker lathe, but have used many plain bearing machines and they were also fantastic. Just wanted to point out that plain bearing doesn't equal lower precision; it is in fact the opposite.

[david]

This is a Derbyshire instrument lathe. It is one of the finest and most precise lathes in the world.    Derbyshire began as Webster Whitcomb which is where WW style lathes came from. Around the late 1940s ball bearing technology, along with the manufacturing of ultra precision spindles,   allowed lathe spindles to rotate faster than cone bearing spindles with a dramatic increase in precision.  Up to this point in time watchmaker lathes, as well as instrument lathes, used cone bearings exclusively.  This is no small machining issue as it allowed  the cutter to be  dialed in to achieve the correct  diameter and a precision finish.  This eliminated  filing, stoning  and sanding a part to achieve the final desired diameter.  Removing  filing and sanding operations from the manufacturing process also removed  dimensional and concentricity errors introduced into the finished part from these secondary machining operations. 

david  

[david]

Pointing out that most watchmaker lathes use cone bearings does not address the precision and speed difference between cone bearing spindles and ball bearing spindles. The reason most watchmaker lathes used cone bearings is, until manufacturing technology improved the precision and performance  of ball bearings (around WW2 and post WW2) cone bearing lathes outperformed ball bearing lathes.  Once the manufacture of ball bearings produced high precision and ultra precision bearings, (ABEC 7 and ABEC 9) the situation reversed. Ball bearings now had tolerances measured in  millionths of an inch and could outperform cone bearings. . 

 Both Levin and Derbyshire produced high quality cone bearing watchmaker lathes. Both companies switched to ball bearing spindles for their watchmaker size lathes; but later stopped producing watchmaker lathes altogether.  Now they only produce instrument size lathes. The major reason for this was a drop in watchmaker size lathe sales due to the availability of factory replacement watch parts. Ordering a replacement staff from the watch factory was easier than making it. At this point in time   watchmaker lathes were no longer required to repair watches and were seldom if ever used. They were  reduced to the role of  display items in the store windows of watch repair shops.

Now that watch factories have stopped selling parts to independent watch repair shops, the role of the watchmaker lathe should gain in importance. If replacement  watch parts are, once again, made in the repair shops instead of being ordered from the watch factory,   the role of a person who repairs watches should also be upgraded from part replacer to watchmaker. 

david