The plate is fitted between the  screw on chuck and the indexing head, the holes go to the back which allows the indexing pin to be located in any of the holes when revolving the chuck/shaft assembly, the degree scale provides a guide to the position.

The bottom pictured Unimat SL indexing head the discs with indentations on the circumference are fitted into the back of the head and locked onto the shaft so when revolved the indexing pin locates the indents to allow indexing of the circle, depending of course on the number of indents on the ring, I regularly use 1 with 24 indents.

Emgee

Edited By Emgee on 21/10/2019 15:40:03

Edited By Emgee on 21/10/2019 15:56:14 added pic

Edited By Emgee on 21/10/2019 16:08:13

I suppose that if there are no holes or other detents in the plates shown then one would have to describe this amazing Emco product as an 'Optical dividing head'.

The seller seems averse to showing what the body looks like but it looks to have a very short spindle

Ian P

As Emgee says the back have different mumbers of holes for indexing.

Though the fronts only have angular graduations not hole numbers.

Not sure what is disappointing about the U3 but having one edge that fits directly to the lathe bed was often usefull to me in the past as were the other mounting options eg the two cap heads that can be seen allow it to fit the cross slide. As well as the ability to set it to any angle as shown on the face of the wheels not just what was covered by the index holes. having the standard M14 x 1 spindle nose is also a big improvement as you can easily fit any chucks or face plate with work left in them, with the SL you would have to take work off of it to get at the 3 mounting screws if you wanted to index an part that had been turned on the faceplate. With the U3 just unscrew from lathe spindle and screw onto indexer.

Edited By JasonB on 21/10/2019 17:47:39

It's only the black coating that has come off, no sign of wear in the metal, more a sign of me not pulling back against the pin's spring enough than a problem.

Also compared to the vast number of 5C spin indexers in use the plates are far less "flimsy" being of similar thickness but much smaller diameter. Again like the 5C indexers the holes are through holes but just covered by the scale disc in both cases the pin does not go full depth into the hole, think more like the pin on a dividing head's arm.

None of the sellers pictures showed that the disks had holes (other than at the zero position?) and I'm always wary of sellers not fully describing items so I thought this Emco product relied on the users eysight. In reality having anodised labels is a good feature.

Ian P

I'll take you a close up photo tomorrow. The pin on the Emco is tapered so may have worn the black off around the holes too

.

… or the original Unimat SL version ?

MichaelG.

It won't be easy to mount the old style onto the new style lathe bed but should not be a problem if you want to mount on the cross slide or milling table.