Sunday, December 20, 2015

Lathe Chuck Back Plate

Building a back plate for my 4-jaw chuck

Difficulty Level (Easy, Medium, Hard, Insane):

When I got my metal lathe it unfortunately didn't come with a 4-jaw chuck which is fine for most jobs but any time a job requires an off-center or square piece of stock, a 4-jaw chuck makes life a lot easier.

I ended up buying a cheap-o chinese 4-jaw chuck at Busy Bee Tools but still had to mount it on my lathe. Luckily, I bought a bunch of metal blanks at one of the auctions I went to recently. However, since this was one of my earliest projects it took me forever to do and when I finally finished I realized that my digital calipers had unfortunately zeroed out at 4 thousands instead of 0 which meant that the final size of the alignment rim was 0.004" over sized.

I thought maybe I could make it work, but because it was the base for the chuck on which all other work would be turned I realized that it was not going to be accurate so unfortunately I had to start the project all over again.

The second attempt went a lot faster but it still took me about 5 hours to do and just when I was getting ready to do the final cut, being very careful the calipers were zeroed properly I mis-calculated my adjustment and bored the center alignment hole 20 frickin thousands over!!! I was so mad!

So I started the 3rd attempt. It went faster than the first two and probably cranked out the part in about 3 and a half hours and this time it was perfect! Normally I wouldn't be as picky when it comes to metal working but because any inaccuracies in the chuck back plate would be affecting all other work done with that chuck I wanted it to be perfect and after about 15 hours of machining I finally had me a proper 4-jaw chuck.



The disc as I got it at the auction
Facing to size
Facing the second time
Ready for cutting the 8TPI 1.5" diameter inside thread
Another view before starting to cut the inside thread
The finished back plate (0.004" over sized)
Close-up of the internal 8TPI 1.5" thread
Close-up of the finish
Drilling the mounting holes for the chuck
And my 3rd try with the 0.004" over-sized back plate beside it
Turning down the hub 50 thou at a time
Getting ready to cut the grooves
The grooves cut and the tightening collar installed
Another view
Laying out the holes for mounting the chuck
The finished back plate (L) and the over-sized one (R)
The chuck mounted on the lathe
Another view
A close-up of the back plate

Drill press
Metal lathe
Metal scribe
Digital calipers
Alan keys

1" thick by 5" diameter metal disc




I guess the third time IS the charm


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