Indexing device for Drummond lathes..

[John Hill]

Can anyone identify, recognise or even explain this indexing instrument?


IMGP9971 by aardvark_akubra, on Flickr

It came with my Drummond 3 1/2" lathe of about 1908, I am sure it is not original to the machine and it has a couple of flaws indicating that it is shop made item. The centre bore diameter and the two holes indicate it is intended to the mounted on the spindle or mayb e one of the change gear positions (which presumably would increase the range of choices for those with suitable mathematical skills).


IMGP9968 by aardvark_akubra, on Flickr

It has a number of circles of index holes, 3, 4, 6, 8, 12 and 60. These strike me as having rather a lot of redundancy but maybe there is something I do not understand.

There are also parallel rows of holes in two places, one of these rows is obviously not on a radial line, again somewhat puzzling.

The front(?) of the instrument has a moving cursor complete with an extension which presumably bore against a fixed point on the lathe. Clearly this cursor is intended to be used with one of the parallel lines of holes as they dont quite line up on the other.


IMGP9969 by aardvark_akubra, on Flickr

The rear(?) of the instrument has another movable arm that can be locked to any hole position. This arm is fixed to the hub and provides a means of fixing the position of the disk in relation to the lathe spindle. The non-radial line of holes line up with this arm.


IMGP9970 by aardvark_akubra, on Flickr
I will be very grateful if anyone recognises the design and can point me to some information that would help me to understand how this device is used as the complexity leads me to believe it can be use for much more than multiples of 6 and 45 degrees.

Thanks