John, the 1.4375" dimension is of the large end although I have not measured it myself to confirm. The taper data was supplied by a J&S legacy dealer who also supplied a few other details about my machine which actually surprised me as I had no idea such details would be on record. This was the email he sent me: –
Hi Chris
Apologies for the delay
The serial number was correct but the sales order number is BO55567. Ex Coventry Education, 1964 1310EIU.
Supplied with
UJ8022 Hardinge 3C340 Collet system.
34628-105 Collet Draw Tube
34771-104 Collet Adaptor Plate
The taper in the workhead is 1.4375" 3.1/2"/foot.
Incidentally here are some other part numbers on the machine
UJ8021 Workhead
34567-001 Blank Backplate
Unfortunately we do not have stock of any of the above, and cost for a 1-off new collet adaptor plate I would expect to be in the region of £1200.
Best Regards
Alan Fisher