Chuck backing plate/adapter nomenclature

PHPaul

PHPaul

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I did a search but couldn't find a topic that appeared to address this. Might well have missed it, if so, sorry.

I see various terms used for backing plates such as "D1-4" and the like. Is there a chart or other reference that explains just what that means?

Having gotten my freebie lathe running, I'm thinking I'd like to get a decent 3-jaw scroll chuck for it, but need to know more about the topic to make an intelligent purchase.
 
Both your lathes have screw on spindles so no "D" backing plates there. Just measure the diameter and count the threads in one inch and you'll have the size you need.

I bought a 4-jaw with backing plate attached for my Seneca Falls Star 9 x 5 and fretted over how to bore it out and cut new threads. I finally bought a tap the right size and took it over to my local jobber machine shop where they made short work of it.

Hope that helps.

John
 
matthewsx said:
Both your lathes have screw on spindles so no "D" backing plates there. Just measure the diameter and count the threads in one inch and you'll have the size you need.

I bought a 4-jaw with backing plate attached for my Seneca Falls Star 9 x 5 and fretted over how to bore it out and cut new threads. I finally bought a tap the right size and took it over to my local jobber machine shop where they made short work of it.

Hope that helps.

John
Click to expand...

Thanks for that. That may be an option for me. The method of attaching the backing plate to the chuck and the spindle diameter are completely different between the two lathes. I had a half-baked notion of being able to swap chucks between lathes, but that's probably not practical as the process of truing them up when swapping backing plates is probably more trouble than it's worth.
 
A tap may be used for finishing a thread in a backplate, but not for doing it from scratch, as taps seldom start entirely straight; you backplate would likely wobble if done from scratch; on all the lathes that I have owned, I have had to make backplates for new chucks, except two that had D and L mounts; I would take a 3 wire measurement or use a thread mike to measure the spindle and then make a plug gage to the exact size and fit the new threads to it, allowing a free but non shaky fit, for the straight portion of the fit, take care not to fit that too tight, I have seen spindles that were galled from too tight a fit and likely dirt or chips caught in the close fit.
 
I was worried about not getting the tap straight and worked out a couple of ways to do it. In the end I took it over to Toolmaster machine shop here in town and they did it for me. It runs as true as my lathe can possible achieve.

John
 
The way I do it is to make a backing plate a little larger that needed. Then thread it, screw the backing plate onto the lathe and do the final machine work to the backing plate so it fits the chuck. Works great every time.


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