Emco Unimat 3 Headstock Dividing Plate

I’m not sure why Emco never made a headstock dividing plate for the Unimat 3. They are an essential part of a clockmakers/watchmakers lathe, found on most 8 or 6mm lathes and some larger ones e.g. Schaublin.   They are invaluable for locking the headstock at a particular angle, for cross-drilling, off-centre drilling, filing squares, hexes etc, checking/modifying/recovering the accuracy of gear-wheels etc etc.  Many years ago I made one for my Unimat, steel for the plate, tempered spring-steel for the detant. That has dug me out of so many technical holes.  

I am now refurbishing a spare Unimat, looking to reproduce and improve on some of my tried and tested accessories using 3d Printing.  The headstock dividing head was top of my list.  

This one has a good range of divisions: 12, 26, 42, 46 and 60.  Including the factors of these (achieved by skipping a set number of holes) this gives the best range of steps I could come up with on a small plate.

It seems to take the conversion to plastic surprisingly well, now a permanant fixure. It has a a similarly secure ‘feel’ to the steel one when locking.  The detant locates positively, and its pin takes a fair amount of abuse - in any case it’s easy to print another one.

Materials

PLA seems to work best, the stiffness really counts for both Plate and Detant.

Fitting:

The Plate fits on the spindle between the pulley and the headstock.  It needs 3 x M4 grub-screws, 1 longer than the others.  Mine are 7, 5 & 5 mm but the lengths are in no way critical, so long as they don’t protrude.  The longer one fits into one of the Tommy-bar holes in the spindle stoping any possibility of unwanted rotation. Fit this first. The other two tighten against the spindle to provent movement.  I cut all 3 grub-screws out of a single longer bolt, slotting the ends with a junior hacksaw to allow them to be driven in.  

The Detant is attached to the headstock using a 22mm long M6 hex-socket screw. It fits into the tapped hole on the end of the Unimat Headstock below and in front of the spindle, just above the leadscrew drive hole. 

To fit:  (Remove the outer cover for the pulleys - it doesn’t do anything apart from get in the way)

Plate: Unscrew the pulley.  Slide the Plate onto the spindle, with the grub-screws partially located.  Slightly tighten the longer grub-screw so that it locates one of the two Tommy-bar holes.  Replace the pulley, this will push the Plate into its correct position.  Tighten the grub screws

Detant:  Fit the hex socket screw so it protrudes 1-2mm from the hole in the detant.  Locate the protruding screw in the headstock tapped hole.  Screw in - the head of the hex bolt touches the side of the plate. Leave loose until you need it.  (If that bothers you, its easy to remove without touching the plate.

Use:

Raise the Detant so that the pin locks in place on your chosen range of holes.  Tighten the hex-bolt fully.   Pushing back on the detant lets the spindle move until the next hole is presented.  For factors count holes.   i.e. to get quarters use every 3rd hole of the 12 range.