Looking for backplate input for a couple 6" auction aquisitions

lsneon · Nov 5, 2020

Bought a couple 6" chucks at auction that both need back plates in 1-1/2.
They were cheep and I thought the reversible jaws would be very handy.
The 4 jaw is a Union and is probably worth more than I paid for both.
It has a back plate but it appears to be 2-1/4. The back plate bolts all
the way thru the chuck with 4 x 3/8 bolts. The 3 jaw scroll only has 3 x 8mm
bolts out at the very edge - seems kinda lite to me especially if its going
into CI which some of the blanks are. The 4 jaw BP appears to be steel which
to my thinking makes more sense. soooo. . .
1. steel v. cast iron
2. pointers or pitfalls to look out for in fabing one

thanks to all that contribute
lsneon

mattthemuppet · Nov 5, 2020

most people will say cast iron, as that's what they're usually made of and the threads won't gall on the spindle, but steel has worked fine in my experience. Unfinished backplates are available for not too much money ($60 or so?), so that's another option. Finally, you could put the backplate you have up for trade for a 1 1/2 - 8 backplate. You never know, someone might have the opposite problem to you!

SLK001 · Nov 6, 2020

lsneon said:
The 3 jaw scroll only has 3 x 8mm bolts out at the very edge - seems kinda lite to me especially if its going into CI which some of the blanks are. The 4 jaw BP appears to be steel which to my thinking makes more sense. soooo. . .
1. steel v. cast iron
2. pointers or pitfalls to look out for in fabing one

The bolts don't do much holding - the recess in the chuck body closely mates with the backplate to do the majority of the holding. The screws just keep things from randomly coming apart.

The recess and the backplate should be a very tight tolerance (line-to-line, if you can hit it)- this is what registers your chuck. Carefully sneak up on the final dimensions.

garyphansen · Nov 6, 2020

Why bother making back plates when you could make an adapter to screw into your existing back plate with 1 1/2" 8 threads per inch internal threads. I have seen this done before.

k3vyl · Nov 14, 2020

Another thing I have done is make the plate from an old pump shaft coupling half. The motor side is usually bored out too big for 1 1/2" 8 threads. These things have keyways in them so don't try to drill them out to the starting diameter. Use a boring bar to open it up, not a big twist drill.

lsneon · Nov 14, 2020

will check it out. everything I have is just a bit too small or waaaay too big.

gph - adapters scare me, little off here, little off there and error starts multiplying -
especially on me.. . .
mainly I was wondering about CI. I have 4 chucks and all the back plates are steel.
doesnt matter rt now, phones been ringing and I'm up to my ass in alligators and
will be till next yr. ohh well.
lsneon

k3vyl · Nov 14, 2020

CI is the thing to use if you can get it.Soft steel could possibly gall.The possibility is small,but the consequences are big.I have one old chuck that has a steel body plate with a CI slug in it. Was worth the work to have a 4" 3 jaw chuck on a 13" lathe for quick change over from collets to rough something in.

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Looking for backplate input for a couple 6" auction aquisitions

lsneon

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