[How-To] Anyone converted a 3j 4" chuck from back mount to front mount?

O

owlshop

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I have a 4" 3jaw chuck threaded holes in back . I need to mount it on a backing plate for a 2 1/4-8 spindle. It looks as
if I can drill the mounting holes thru to the front of the chuck with out hitting anything operational in the chuck and
then counter bore for allen head on the front. The bolt circle is 3.31".
Thanks for any reply! OWLSHOP.
 
This is what I did for a 5” 4 jaw chuck to install on my 6” rotary table.
Works excellent.
EDIT: better check twice before drilling. Mine was a 4jaw independant I had no scroll to worry about.
 
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The bolt circle will be 1/2" outside of the threads. That should be plenty of room to have the bolts on the backside. You may have to countersink the bolts in the backing plate for clearance issues. What is the reason that you are thinking you need to come in from the front?
 
I did a similar thing for a friend. He drilled the backing plate first. Then I took a facing cut . A 1" MT milling cutter holder was installed in the tail stock. Then a 6" piece of 1" drill rod installed in the MT. The chuck was tightened on the drill rod . Shellac was brushed on the backing plate and the tail stock with the chuck was pushed up to the face plate and left there for 3 hours. This centered the chuck on the face plate.
He unscrewed the chuck and backing plate . He clamped the backing plate to the chuck before drilling and tapping.
This method allowed the back plate to be fastened from the back and the chuck centered on the backing plate.
He told me that when done the chuck was .002. That's good enough for a 3 jaw chuck.
If I was in my own shop I would have used hot hide glue instead of shellac. Shellac worked as the chuck 3" 3jaw and was not too heavy. I used what he had available.
mike
 
mickri said:
The bolt circle will be 1/2" outside of the threads. That should be plenty of room to have the bolts on the backside. You may have to countersink the bolts in the backing plate for clearance issues. What is the reason that you are thinking you need to come in from the front?
Click to expand...
I thought that I would have to thin the spud on the back side of the backing plate to clear the bolt heads and was
unsure how thin would be to thin for the threads and cast iron. OWLSHOP
 
I noticed you only have a few posts. Welcome to the forum. You will find lots of friendly people on here that will help you out with any questions you might have.

A picture of the back of the chuck would be very helpful. Does the chuck already have a backing plate? If it does you want to duplicate that backing plate with 2 1/4 x 8 threads.

The backing plates on my 3 jaw chucks are 5/8" thick. The backing plates are held to the chuck with machine screws, not bolts. And the screws are countersunk into the backing plates. The most important part of a backing plate is where it registers into the chuck. This needs to be a very tight fit. The screws merely hold the backing plate to the chuck.

We will help you get this figured out.
 
mickri said:
I noticed you only have a few posts. Welcome to the forum. You will find lots of friendly people on here that will help you out with any questions you might have.

A picture of the back of the chuck would be very helpful. Does the chuck already have a backing plate? If it does you want to duplicate that backing plate with 2 1/4 x 8 threads.

The backing plates on my 3 jaw chucks are 5/8" thick. The backing plates are held to the chuck with machine screws, not bolts. And the screws are countersunk into the backing plates. The most important part of a backing plate is where it registers into the chuck. This needs to be a very tight fit. The screws merely hold the backing plate to the chuck.

We will help you get this figured out.
Click to expand...
Long time reading posts. No back plate on this chuck . I have fitted backplates to about half doz. 5"6"chucks for 2 1/4"-8
and 1 1/2" spindles and adapted a regular back plate to a Bison 6" 6jaw set-tru chuck. Was not sure about this little
4" chuck on the 2 1/4" back plate. I have a back plate 6" for 2 1/4" but it look like I would be drill/mill into the spud
for the allen head screws. I found a 4" backplate for this chuck with 2 1/4"-8 threads but they sold the last one before
I could get it on order. OWLSHOP>
 
I have now had time to disassemble the 3j chuck .There is nothing internal to stop me drilling thru the chuck to
convert it to a front mount chuck. If I do not convert it to a front mount I can bore into the outer edge of the
2 1/4" hub on the back plate to clear the heads of the allen head bolts to mount from the back. OWLSHOP
 
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