Originally posted by John Echternach:
The runout on the Taig headstock is reported to be better than .0005". The reports from the manufacturer and from users is that it usually exceeds that number(.0003" to .0005").
Hi John,
My Southbend "Heavy 10" (10L) specs specs less run out than that! For those that don't know what a 10L is, it is a mid priced engine lathe with a 10 inch diameter swing. I wouldn't use it to replace a pivot on a watch.... Well, not anymore ;-)
The runout of a typical cone bearing is 1 or 2 /100,000ths of an inch. That is, 0.00001-2". The typical high quality ball bearing watch lathe, such as a Levin, will have 0.0001" maximum runout. Just as a point of reference, bearings of the same size and quality as those that go in a Levin lathe cost about $120 each. The Taig lathe, in a simple form, costs about $400. I rather doubt that they have spent 1/2 the sales price of the lathe in bearings.
Now, why do we care? Well, the runout of a cone bearing shows up as the spindle's mechanical axis revolving around the true rotational axis. The runout of a ball bearing is complex. You get an axial component that is just like the cone bearing's, but you also get a component that appears to be random, called rumble. Rumble is due to imperfections in the spherical nature of the individual balls.
The axial runout shows up as an eccentric offset when you take a round piece of stock, and turn a diameter. The rumble shows up as a rough surface finish. Both are show stoppers when you are trying to put a new pivot on the arbor of some wheel in a wrist watch.
[On the bright side, you can get some really cool looking moire patterns on a fine turning on a ball bearing lathe (using power
feed).]
It happens that the cheaper bearing (cone bearing) is the better bearing for a watch maker's lathe. Ball bearings are a better bearing for bigger lathes that take heavier spindle loads.
-Chuck
Steven ThornberryUser Administrator