Making a backplate for an ER40 set tru chuck

The replacement chuck came in today. Much better! No grooves, no rough spots.
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Need to box up the old one and ship it back. Shars sent me a free shipping return label. Tomorrow, get to work on finishing this up! Moment of truth, gulp. I get to check how good of a job I did on this backplate.
 
As it turns out, I did ok. Installed the chuck on the lathe. Indicated the 5" OD to get close to true, adjusting with the 4 set screws. Managed under 0.0001" TIR measured by my Interapid DTI. Checked the taper and the TIR was similar on the one point I checked. Put in a ground 20mm rod (my Rollie's Dad Method bar) into a 20mm collet and tightened it. Really need a better setup for tightening, might actually drill three holes in the chuck itself for a tommy bar. But first I have to convince myself that everything checks out ok.

Measured the ground bar TIR at 0.0005" next to the collet. So the collet or the collet + bar are near the guaranteed TIR of the collet. Considering that I don't think I am at the correct torque for the nut, it seems reasonable. To check the rod, I can indicate it in a pair of vee blocks. Curious what I might find. Thinking the error will be mostly in the collet, but I'll indicate the rod.

Also will turn down the diameter of the backplate. It seems to be about 0.017" greater radius than the chuck.

I suppose, before I get all giddy, I should try removing the assembly from the lathe and reinstalling it. (I am not removing the chuck from the backplate!) And perhaps reinstalling the collet and rod. Hopefully the TIR won't be worse.
 
Loosened the nut until collet could move. Rotated the collet 180 degrees, but didn't rotate the rod relative to the collet. Retightened and measured TIR. 0.0002". Might have been a burr or piece of crud before. Or an excentric collet. Still, it made me feel better ;).
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Turned the backplate to diameter and re-chamfered the edge by the headstock. The backplate is done! This project is complete. Was a fun job that I didn't think I was quite ready for. Very happy with the way it ended up.

Now I really need to clean up this lathe. Just been vacuuming and cleaning the ways. Have to clean off the fine stuff that doesn't wipe off easy. The stuff that makes the paint look darker.
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It’s been fun to watch, thanks for sharing. I imagine you will really like having the ER chuck. I have just a drawbar 5C and it’s nice to use when appropriate.
 
jwmelvin said:
It’s been fun to watch, thanks for sharing. I imagine you will really like having the ER chuck. I have just a drawbar 5C and it’s nice to use when appropriate.
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Thanks for your gracious comments. I really liked the ER32 I got for my mini-lathe. Found it to be a lot more useful than I expected it to be. Made the mini a joy to use.

When I got the G0752Z, I knew I wanted to put in another ER chuck, but a little bigger. I did find that the ER40 collets seem to be stiffer than an ER32, there was a bit more resistance to popping the collet in and out, but that may be a function of the collet nut I have. It was a bit of a struggle to acquire the chuck and backplate due to pandemic related sourcing issues. I'm glad I ended up machining the backplate from scratch, as I learned a lot from the process. It was a great experience and gave me a lot more confidence in my machining abilities.
 
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