Backplate for Myford 254 lathe

Robert Walker finds himself having to make a backplate for a newly purchased chuck.

- Robert Walker

As a member of the Beeleigh Mill Restoration Group I had a requirement to make some square-headed bolts with non-standard pitch threads to replace broken or missing bolts for the steam engine. See this website for further details of the mill and its engine: beeleighmill.co.uk.

The engine was made around 1830, hence the nonstandard threads. A number of articles in Model Engineer discussed the usefulness of four jaw self-centring chucks so I decided to buy one to simplify the manufacture of the bolts. The problem I had was my lathe was relatively old and had the BS 4442 Type-A small cone to locate the chuck with three studs and nuts to retain it. As I could not find a backplate available commercially I had to make my own.

The starting point was to find the specification of the spindle nose. I was fortunate at this point as I still did some part-time university lecturing so I was able to access the appropriate British Standard via the university library. The Myford manual for the lathe also states that the clearance between the face of the backplate and the spindle nose flange should be 0.002 inch. The material I chose was 5 inch diameter mild steel, 1 inch thick. For the studs I decided to use three countersunk head set screws fixed with permanent Loctite 658. As it happened the screws were too short so I used three M10 bolts I had in stock, with the heads cut off and machined flush to the surface.

The chuck I bought was 125mm diameter so a 5 inch blank would allow the outside diameter to be skimmed for appearance. On my existing chucks the tapered recess is 12mm deep and the cone on the spindle is 10mm high but to ease manufacture I replaced the recess with a hole as shown in fig 1. The recess in the back of the new chuck is 5mm deep and 95mm diameter therefore the chuck is located radially on a 95mm diameter recess and the face is between the 95 and 125 diameters.