[How-To] Threading a chuck backplate

[Jim F]

1) new chuck
2)my 4 jaw
3)my 3 jaw
4)my dog plate
5) my spindle

 

[Jim F]

I was figuring I would need to get a backplate when I bought it, so it is figured into the deal.

 

[mickri]

The fit of the threads on the backing plate are not that important. You actually want a loose fit on the threads so the backing plate fits tight on the register of the spindle. You want a tight fit on "A" in the picture and that the backing plate fits square/flush to "B" in the picture. "A" is the most important fit. Once you have the backing on the spindle then you machine it on the spindle to fit the chuck. The chuck will also have a register that the backing plate has to have a tight fit. "C" and "D" in the bottom picture has to have a tight fit.

 

[Shootymacshootface]

If all you need to do is clean up the threads, you could buy a nice live center or some other tooling with the leftovers .

 

[Jim F]

The fit of the threads on the backing plate are not that important. You actually want a loose fit on the threads so the backing plate fits tight on the register of the spindle. You want a tight fit on "A" in the picture and that the backing plate fits square/flush to "B" in the picture. "A" is the most important fit. Once you have the backing on the spindle then you machine it on the spindle to fit the chuck. The chuck will also have a register that the backing plate has to have a tight fit. "C" and "D" in the bottom picture has to have a tight fit.

View attachment 351120

View attachment 351126

View attachment 351127

I took the backplate off, it is not very tight in the chuck register.
It is thick enough I can re-turn the chuck side, if I can get it to thread onto the spindle.

 

[mmcmdl]

Mickri is correct . If you have a internal threading bar , set the lathe up for threading 8 tpi and pick up the existing thread . Run it thru by hand just to clean it up . The thread can be loose as the register diameter is most important .

 

[Jim F]

Mickri is correct . If you have a internal threading bar , set the lathe up for threading 8 tpi and pick up the existing thread . Run it thru by hand just to clean it up . The thread can be loose as the register diameter is most important .

Just went out and looked again, the chuck register is tapered, and fits tight when seated, so I cannot re-cut that side.
I think I will try to get a 1 1/2 -8 bolt to use as a thread gauge, I used a 1 1/2-8 nut for a thread protector and it fits the spindle nicely.

 

[mmcmdl]

The threads on the new back plate look like garbage after blowing the picture up . Run a small wire wheel around those threads and clean them up . It may be all you need to do .

 

[Jim F]

Mickri is correct . If you have a internal threading bar , set the lathe up for threading 8 tpi and pick up the existing thread . Run it thru by hand just to clean it up . The thread can be loose as the register diameter is most important .

But I will have to touch oily gears and get dirty..............

 

[mmcmdl]

If you have any amount of #^%@ on those threads , say .0005 , it makes the PD close up by roughly .003 . I used to machine threads that required plating of different sorts , and if I remember correctly it was a 4 to 1 ratio .