View Full Version : Making a Two Piece Back Plate - Need Some Clever Ideas

02-20-2011, 07:54 PM
Had a customer ask me if I could make an adapter plate to bolt a plain back 10" three jaw chuck to. The spindle is 2-5/8 by 6 tpi threaded nose.

To keep material costs down, he wanted to use two pieces of cast iron. I have a 6" long piece of 4.75" diamter durabar and a 1" long piece of 10.5" diameter durabar.

I was thinking about machining the plate with the boss, bolt holes and a tapered center hole. The taper would be very slight - i.e. it would be self holding and it would drive the plate.

The smaller diameter piece would be bored to fit the spindle nose and it would have a male taper machined on it. The tapers would insure that the two pieces fit together with a minimal amount of runout.

The question is how to hold the two pieces together. Do I braze them or ... ? I don't want that taper to accidentally come loose and throw the 10" chuck at the operator!

John Stevenson
02-20-2011, 08:11 PM
Taper, loctite and some recessed allen bolts thru the plate into the boss section.
The final face skim and register will have to be done on the donor machine anyway.

Don't braze.

02-20-2011, 08:57 PM
To John's suggestion I'd add some dowel pins so that the bolts are not taking all the shear as well as the secondary function of taking out any play from the bolt clearance holes.


Tony Ennis
02-20-2011, 09:03 PM
Won't the extra time for you to do this job pretty much erase any cost savings compared to just buying the right backplate?

02-20-2011, 09:09 PM
To keep material costs down, he wanted to use two pieces of cast iron.

DuraBar is about $1.50/lb. How much are you charging him for labor?

That's a rhetorical question :)

Don Young
02-20-2011, 09:10 PM
For additional safety you might make the tapers reversed, larger diameter away from the headstock. Then release of the tapers would not free the chuck. Or perhaps even have a flange on the outer end of the center part which is larger than the hole thru the outer part. Of course the fitting and assembly would be a little more involved.