Chuck Backplate

MozamPete

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Jun 26, 2014
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I have a Grayson lathe (cira. 1930) which I recently brought to temporarily keep me amused (I'm moving countries so don't have all my normal machines and tools at present and thought this would be good to keep me busy, tidy up and eventfully pass on when I ship my stuff over). Main positive is that is has a lot in common with my Myford (same spindle thread, same change gear size/DP, same T slots on the cross and top slide, etc) so any tooling I buy or make I may keep when it arrives so wouldn't be a total waste.

It came with a small 3 jaw chuck and I have brought a larger 4 jaw and now need to make a back plate. Problem is I don't have the reverse jaws for the 3 jaw chuck, so holding a larger backplate to machine it is going to require some fiddling.

Spindle nose is a 1-1/8", 12 TPI thread. I have a 4" 3 jaw chuck (without the reverse jaws) and a 5" catch plate, but no face plate. New backplate is for a 5" chuck and my raw stock is 6" diameter cast iron. If it works I may also make myself a 6" face plate.

Here is the order of operation I have come up with which I think will work but I'm open to any suggestions/improvements/alternative.

1) Cut a copy of the male spindle thread as a basic go/no go-gauge for when doing the female thread so I can test it without having to remove the work piece (already done this).

2) Cut a ~35mm slice of 6" dia cast iron. I have some material but only have a portable band saw so will set up some type of jig/guide to cut it as even as possible to start off with.

3) Drill a hole in the center of the stock - probably about 16mm diameter.

4) Mount in the lathe, against the catch plate with a draw bar through the spindle. Will turn up something with an OD that is a close fit to the hole in the stock and the hole in the center of the catch plate to make sure it is aligned central. Draw bar will be M12 threaded rod (M16 is too large for the spindle bore). This is the first sketchy bit but I can't see any other way I have available to hold it. May use some double sided tape or hot glue between the catch plate and the stock to maximise the friction.

I did consider turning between centers, with a drive fixture bolted to the outside 1/2" of the stock (which ill eventually be turned down anyway), but I'm not sure how stable that would be as it is wide and short. I could still add a positive drive to the above if the friction wasn't enough to stop the stock slipping.

5) Turn the outside of the collar on the back down to around 45mm

6) Turn the workpiece and hold it by the collar in the 3 jaw chuck and bore and thread the inside 1-1/8" 12TPI all the way through. Do an initial facing cut on the front to smooth it out.

7) Turn the workpiece and thread it backwards on the spindle, face the rear surface on the collar and bore out the register diameter. This is another sketchy bit as I would much rather do the threading and facing/boring of the back surface in one setup but can't see anyway around it. Will need a spacer on the spindle to allow the back plate to only partially thread on (so I can bore the collar) and as that side of the back plate wont have the proper register diameter to bottom out on (but will at least be flat as I faced it in the previous step).

8) Turn the workpiece and thread it on the spindle fully home the correct way around.

9) Face the front and turn the register diameter for the 4 jaw chuck. Turn the diameter down to size.

10) Fit, drill the mounting holes and and bolt on the chuck.


Well that's the plan at present but will probably keep thinking about it and doing some prep until the weekend when I would have time to really get stuck in.

Is it going to work? Am I missing something obvious and making it harder than it needs to be?

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Your careful planning will pay off and your sequencing seems right to me. One other thing: Gray matter is
way more active at night and I see you have given your brain time to study the details of the operations. I fully expect
it will turn out just fine. I wish you the best of luck.:encourage:
 
could you possibly attach a flanged stub to the rough sawn disc? This would allow you to hold the stub in your current chuck while you face, bore, thread, and cut the register, all in one set-up. if the flange was large enough, the bolt holes would be outside the threaded stem of the new backplate, and not interfere with the eventual chuck mount. Worst case, you might need to do some facing cuts on the headstock side of the backplate after it is on the spindle.
 
could you possibly attach a flanged stub to the rough sawn disc? This would allow you to hold the stub in your current chuck while you face, bore, thread, and cut the register, all in one set-up. if the flange was large enough, the bolt holes would be outside the threaded stem of the new backplate, and not interfere with the eventual chuck mount. Worst case, you might need to do some facing cuts on the headstock side of the backplate after it is on the spindle.
That is sort of what I would of done had I had a faceplate - bolted through the faceplate directly into a part of the stock that would be eventually machined away.
But if I had to buy anything to actually machine it then it would be easier to just buy a machined backplate. As it is the economics are marginal, cost me about a third of the cost of a machined backplate just to buy the cast iron for one.
 
Well I got step 2 and 3 done today.
I had tried to buy some 5” cast iron and all they had available was 6” so I said OK - hadn’t thought it threw that my portaband only has a 5” throat. So cutting became a bit of work. Set up my saw as I had intended, shimmed to the thickness I wanted and cut as much as I could, then hacksaw for the middle 2-1/2” that the band saw couldn’t reach.593E7946-7378-47E4-954B-6689F2BBA8C2.jpeg
102B9927-A5BA-4E45-BB0B-3021972CA537.jpegDrilled a hole in the center.
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And ready for the lathe.
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Got steps 4, 5 and half way through 6 done on the weekend.
Slow work, at the larger diameters I could only take very light cuts (5 thou) without the belts slipping and the chuck stalling. May need to try cleaning the belt as it seems to have got a bit of oil on it over the years which I don’t think was helping. Got better as the diameter decreased.

4DEF1AA8-2C8A-43D1-8427-D98956160D66.jpeg

C8FDE0BB-59AB-4ACA-AAC9-A77C2A333934.jpeg
 
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