Does anyone have a source for a back plate for a Lot 4
A semi finished one would probably be preferred but the 1.25X 12 threaded hole is the key feature I need.
I thought I had one lined up but it seams to have evaporated.
TIA Greg

I've not seen one anywhere with the right threads.

Best I've found is either a blank or one with a smaller hole that could be bored out and threaded.

Steve Jordan on Youtube suggests using an exercise weight as a source for a blank.? I don't know whether that's a good idea or not.



You can also get taps of that size, but IIRC, Dennis said the spindle thread is a little off from 1-1/4x12 and it's best to cut it to fit.

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+1 for Dennis’s suggestion of boring the internal thread to fit.

I can see the attraction of the weights.

Backing plate is a pretty simple piece, especially a blank one.? Yet they're like $50 and up.
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That's about 1/3 to 1/2 the price of the associated chuck.

Yet when I take a trailer full of iron/steel to the scrap yard, it barely pays for the gas to get there.

I don't get it.

Does a backing plate need to be cast iron or can steel be used?? Seems like a 4" puck about 1-1/2 long of steel is around $25 on ebay.? Lots to machine away, but it's good practice.

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The last three back plates I've made were made using a somewhat elaborate method, the reason being a backplate for massive old belt drive lathe I could'nt bore/thread on the lathe (no pick off gears), and the other two were for the Select lathe out in the hangar, neither of which I wanted to go back and forth with a dismounted backplate to test on it's spindle.

?My method worked so well I'll probably do it again for every time it comes up.

?I took a scrap piece of round bar big enough to make a thread on one end and a turned copy of the register area on the other end, and used a thread mike with exceedingly careful and numerous thread diameter checks on the threads of the spindle. The register area I likewise carefully measured.
?In both cases when I got the plug gage made thus I used it to bore and thread the backplates on my lathe at my shop.

?My goal was a thread and register that only just goes on by hand, and used antiseize compound lightly in case it wanted to gall. Neither needed the antiseize though, and both were as close to a perfect fit as I've ever done and on the first try. Normally I've taken it out and tried to fit it to the spindle and then re-chuck carefully and try a bit more etc etc.

?When I was done with the one huge lathe's backplate I gave the plug to my customer, he protested he'd never need it again but I insisted, since he paid for it and it may come in handy.

?The 1 3/8" plug I made for the little select I oiled up and placed in a box under the lathe.

?Please let me ramble on a bit, because I learned a new method to turn a cheap chuck into an adjust-true type chuck recently.

? Because I had bored and threaded the chucks backplate I turned the register to be a slight press fit into the back of the chuck, yet even so the chuck itself had runout .015" at 4" away from the jaws so I knew it wasn't accurately made. This is a three jaw which runs true just outside the chuck jaws, so I know the jaws tenons aren't true to the axis.

?What to do? I'd turned regular chucks into adjust true chucks before by using setscrews at four places that bear against what would be a register, but of course the register needs a few thousandths of play to make that work, and typically backplates aren't thick enough to have 3/8" to 1/2" registers sticking out, most small chuck backplates are more like 1/8" stickout.

?But even having two small setscrew at each of the four points is shifty because they don't have much area. because that shoulder only extends 1/8". If they can, Under heavy turning things will move, adjust tru chucks use large area setscrew pads between the setscrews and the registers.

?So I was watching a youtube video () and seeing the long register on the guys backplate, and I wished I had room for one on mine, when it hit me.

?Pretty simple of course, I just trepanned a groove in the face of the backplate and am making a steel ring to bolt down into the groove, then I can used 3/8" setscrews at (The closest to) four opposing points to adjust the chuck with. This ring will be a light press into the face both inside and outside the groove and the length sticking out will be far enough to seal out chips, the chucks inside "chip seal" plate I cut away down to the inside diameter of the ring, but outside the groove the ring will be turned down .015" smaller than the chucks former register, which is the inside of the body of the chuck, and there is plenty or room for the pinions to turn and for the setscrews to adjust the body to run true.

?As for the runout at 4" I'll mark the back plate opposite the largest runout and scrape it until it runs true at 4" or even 8".