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Test 1-1/2”-8 TPI Back Plate?

My Emco-Maier 1-1/2-8 TPI spindle measures 1.498" OD over the threads.

If the Barnes is 1.5+ that might be the source of the problem.
 
The lathe was made sometime between 1921 and 1937, so I’m not too surprised if the dimensions don’t match current standards. It was pretty common back then for manufacturers to use threads that were off just a titch so customers had to buy OEM parts and competitors parts wouldn’t fit.

I think I’ll research doing thread measurements and see if I can identify what I need to do to mate the 1937 spindle with 2026 back plate. I suspect I might end up making up a jig and hand-chasing the Accusize plate. It would just feel sacreligious to modify the Barnes spindle.
 
whydontu said:
The lathe was made sometime between 1921 and 1937, so I’m not too surprised if the dimensions don’t match current standards. It was pretty common back then for manufacturers to use threads that were off just a titch so customers had to buy OEM parts and competitors parts wouldn’t fit.

I think I’ll research doing thread measurements and see if I can identify what I need to do to mate the 1937 spindle with 2026 back plate. I suspect I might end up making up a jig and hand-chasing the Accusize plate. It would just feel sacreligious to modify the Barnes spindle.
Click to expand...
Perhaps find as many backplates and chucks that are that thread size and try them. If you get more than one that's tight I'd adjust the spindle.
 
When I had the SM9 I bought a 1.5-8 nut from a local nut and bolt store to use on the spindle for something I was making. When I went to thread it on the spindle it more or less just slipped over the spindle thread. Turns out the nut hole was 1.5 and then threaded. When I returned it the guy behind the counter said that's the way all threading works,,,,,,,ya right.

I won't mod the spindle but talk with Accusize and if they have no solution send it back and find a used plate to mod.

Do you have a chunk of something around to do a practice thread in? No point in goofing up a good piece until you get the sizing correct.

As to patience, you're retired, got somewhere else to be? lol
 
If they machined the spindle threads to be proprietory, or for whataver reason its an odd size, there are options but lesser of evils. If you have another lathe handy with that thread available you could machine a custom mating thread (with the measrd target measurments in hand). I've seen CI backplate blanks around but not sure how available they are. You could machine a smaller diameter collar, get that right by confirmation fitting & then somehow marry that to a blank of steel representing the backplate. That lends itself to handy scrap materials but welding is the only way I could see joining them. Thats an effort but maybe one adapter is all you need for planned chucks. Or make a new spindle shaft with true 1.8-8 TPI threads & then maybe home free in terms of off the shelf accessories. That way you could simultaneously machine the other standardized critical features like thread length, cylindrical boss length & boss dia because I tink those are likely the datum surface anyway. But, not sure how many fun features to replicate aft of the nose though - bearing surfaces, more threads, keyway slots....
 
I gave up, sent the new backplate back to Accusize. Took the existing backplate and machined to match a new K11-100 4" 3-jaw chuck from Amazon. A bit of mostly careful machining and the end result is perfectly acceptable 0.002" runout. Tested using a couple of chunks of ground shaft from the scrap bin. same 0.002" flicker using a 1/4" o.d. shaft and a 5/8" shaft. Not bad for a lathe built in 1932.


And came up with a reasonable solution for the lack of dials on the crossed and feed hand wheels. A flex holder, dial indicator, some shim stock, and a little chunk of scrap metal. Helped a lot in getting the back plate machined true to match the new chuck.

IMG_5702.jpeg
 
whydontu said:
Anyone have a 1-1/2”-8 TPI back plate that I can buy cheap or borrow? My Barnes lathe looks to have an 1-1/2”-8 spindle, but when I measure it seems to be over 1-1/2” o.d.. I need to get a new chuck for the lathe (the century-old Cushman chuck is beat-up and best I can get is 0.015” run-out) but I can’t justify spending a couple of hundred on a chuck that might not fit.

So if I can find a test back plate or chuck I can confirm if a current back plate will fit, then I can decide if it’s worth buying a new chuck.

Any options put there?
Click to expand...
I have a leftover backing plate for a 4-jaw that was from a barnes #13. You are welcome to have it if you need it. It doesn't fit either of my current lathes so I have no need for it.
 
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