Last updated April 25th. 2012
Screwhead Polishing Lathe
Screws are important part of every watch movement, their pleasing appearance is adding to the looks of it.

Quite a few tools can be, and are, used to polish screw heads to a nice black polish. The most effective and accurate tool in a watchmaker's shop is a screwhead polishing lathe. The set shown below is intended only for watch work, there  of course are similar sets which include larger number of accessories that are used in clock making.

The tool consists of a fixture which is mounted in a bench vice to set it up for work. There is a hand operated runner/spindle with a set of brass collets and a set of brass sub chucks used to hold screws by threaded end. The set contains two laps made of cast iron and bronze. Some Screwhead Polishing Lathes have a third lap made of boxwood that is used for a final step in polishing.  The lathe spindle is rotated by left hand palm, backwards and forwards, while the lap is rotated by the right hand holding it with fingers and at the same time pressing the lap against screw head.  

The iron lap is used first, charged with either the oilstone powder or the coarse diamantine. When finished with coarse polishing the screw head is thoroughly cleaned and then a bronze lap is used charged with fine diamantine powder. 

Cleanliness is precondition for successful polishing, an absolute must.
This image shows a G. Boley Screw-head Polishing Lathe with the set of accessories. 

Cast iron lap, bronze lap, brass collets, brass sub chucks and two lanterns for polishing the threaded end of screws.
Here the Screw-head polishing lathe is mounted in a bench vice with a cast iron lap ready to polish screw heads. 

Instead of laps one can use roller rest (located at front right hand side) for use of file to shape the screw head.

This image shows three tier Polishing Block.  

It has four parts, a cover and three decks each lined with a metal disk.  

Metal disks are used as a base for preparation of the polishing/lapping compound by mixing it with light oil.  

The block is used also as a storage of lapping mixture to keep dust away and to prevent contaminating it.
Here one can see the already prepared diamantine paste, ready to be used on one of laps of the screw-head polishing lathe.
A selection of three grades of diamantine powder. 

Fifteen grams seems to be quite a small quantity, however, it shall last long time and will do a lot of screw heads among many other parts.
Here is a close up of the two lanterns used for polishing the threaded end of the screw. 

Here is also a set of three lanterns which came with my Favorite II lathe.

They do require a larger collet, #55, to hold them while the G. Boley lanterns are for use with collet #33.

Thread on both devices is the same, so the lanterns can be mounted on either carrier and used in the screwhead polishing lathe, thus extending the range of screw sizes.
Here we can see one of the brass collets used for holding the larger screws and two of sub chucks used for holding the very small screws as used in watches. 






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