Lathe Chuck Backplate
Hello,
I have a lathe spindle from an Emco 220P but sadly the drawbar threads on the power chuck was damaged during shipping. (Picture of the spindle nose attached) I've since purchased an old front-mounted Burnerd 35B 4 jaw chuck which I intend to mount on this spindle but I'll need to make a backplate for it as both the mounting holes and locating recesses are different.
The spindle was designed for a 3 jaw chuck and used a total of 6 M5 bolts in three pairs. The spindle also has three M5 plugged holes next to each group and three larger M7 holes in the gaps. The Burnerd chuck uses a total of 4 M8 bolts. (Actually I think the Burnerd bolts are imperial, but it doesn't matter as they are clearance holes anyway.
I've attached a picture showing the bolt holes aligned in CAD with the chuck holes highlighted, sadly the PCD of all of the holes line up which means that I can't use a full set of bolts. My plan was to use all four of the chuck bolts, four of the M5 spindle bolts and one of the M7 bolts in the gap. (Drawing attached showing the spacing of the holes I intend to use - The thickness of the backplate is not final) Will I have any issues doing this, where I'm not using symmetrical bolt holes in the spindle?
As an aside, for the production of this as I don't have a lathe I was intending to make this on the spindle itself. I can see two options:
The first would be to start with two pieces of 100mm bar stock - The first (A temporary mounting jig) would have the holes for the spindle drilled / counter-bored and would be bolted to the spindle directly without any recess being cut. The second (The actual backplate) would be bolted to the first with three bolts within the middle 1" area where the through-bore will be. (I could expand this area to 40mm if needed) - I'd probably also super-glue the two pieces together for extra support. From there the recess for the spindle can be cut and once completed, the spindle mounting holes / counter-bored can be cut in the backplate on a mill. The parts can then be split and the real backplate can be mounted directly to the spindle with its final mounting bolts, allowing the chuck-facing parts to be cut in-situ.
The second option would be to do the same process but instead to start with 100x100mm square plates which can be bolted together in the corners in order to provide a bit more support. The corners can be cut off once the spindle recess has been cut to the correct size.
I'm not sure if the first option would provide enough support. For the first option, I'd start with two pieces of 100x25mm EN3B bar stock.
Thank you.
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