4-Jaw chuck back plate

[NPKenny]

I could use some help with the process of machining the backing plate for my 4-jaw chuck.

It’s my understanding that the benefit of a blank backing plate is that it can be basically machined as part of the lathe to be perfectly true.

I would appreciate any tips on process order, rpm, tooling, etc. Should the mounting holes be tapped, or through holes? Do I tap them before or after indexing? The plate looks to be cast and it is not well indexed to the chuck. The chuck has never been mounted.

I’ve posted this in the chainsaw forum since cutting squish bands and bases was the motivation for learning how to use a lathe.

Thank you!

 

[SimonHS]

This is a link to a good explanation of how to do it. Fitting the backplate to the the register at the back of the chuck is the most important part, but it is most critical on a three-jaw chuck. A four-jaw chuck allows you to centre the workpiece very accurately even if the chuck body is slightly out of alignment.

http://www.lathes.co.uk/latheparts/page7.html

 

[JugHead27]

What he said^

also since you’re interested in learning lathes, check out this mans channel. Good content

https://m.youtube.com/c/Abom79

 

[srcarr52]

You will mount the back plate on the spindle and cut the face flat with a register that protrudes into the inner bore of the 4 jaw (just inside of the bolt circle). You'll want a slip fit from the register OD to the chuck ID and make it a little shy of the depth of the pocket chuck.

Once you have the register cut and the backplate machined flat where the bolts are you can unmount the back plate and drill tap your chuck mounting holes.

Any material after the bolt face is useless, that chuck is made for a smaller back plate. You could cut it all off but that would take forever, I'd just over cut it so it has 0.005" between it and the chuck.

 

[davidwyby]

What these guys said.

You can check out a big machine shop here in Jan if you make it to the GTG.

 

[farminkarman]

You will mount the back plate on the spindle and cut the face flat with a register that protrudes into the inner bore of the 4 jaw (just inside of the bolt circle). You'll want a slip fit from the register OD to the chuck ID and make it a little shy of the depth of the pocket chuck.

Once you have the register cut and the backplate machined flat where the bolts are you can unmount the back plate and drill tap your chuck mounting holes.

Any material after the bolt face is useless, that chuck is made for a smaller back plate. You could cut it all off but that would take forever, I'd just over cut it so it has 0.005" between it and the chuck.

Had to go through this same exercise for my lathe. Once I got the shoulder cut on the faceplate, I transfer punched the faceplate and drilled & tapped the mounting holes. I had my doubts at the time, but my 4-jaw has worked just fine for me.

 

[NPKenny]

What these guys said.

You can check out a big machine shop here in Jan if you make it to the GTG.

That would be excellent. I may even take you up on the offer before then if I end-up back in the Imperial Valley.

Ironically, I spend a lot of time in a pump machine shop. I have great relationships with the machinists, but they rarely humor me when talking about small part fabrication.

 

[NPKenny]

Had to go through this same exercise for my lathe. Once I got the shoulder cut on the faceplate, I transfer punched the faceplate and drilled & tapped the mounting holes. I had my doubts at the time, but my 4-jaw has worked just fine for me.

Thank you! Was your backplate cast? Any fresh experiences on tooling and how you avoid chatter on this material?

 

[farminkarman]

Thank you! Was your backplate cast? Any fresh experiences on tooling and how you avoid chatter on this material?

It is/was cast iron. I just use carbide for everything…works fine for me.

 

[Catbuster]

Here’s a video that should give you an idea of the general process… (It doesn’t help that This Old Tony is very entertaining either):

But the singularly most important thing is that the back plate runs concentric to the spindle. Next is making sure the face is square to the spindle. Once that taper (if your lathe uses one) is cut, the rest is easy. It’s just locating the features and getting them where they need to be to fit that chuck concentric to your spindle.

 

[Catbuster]

Also, @NPKenny, if you’re running carbide and getting chatter but your fixturing is good, add some more feed speed/pressure and depth of cut. A lot of smaller manual machines don’t run hard or fast enough to take full advantage of carbide, especially CNMG and WNMG inserts that are meant for heavy cuts.

If you’re still chattering after that, check your fixturing, which is probably your issue. If it’s still an issue, especially with aluminum, bronze, or other soft material, switch to a high speed steel tool. They’re cheaper, easier to maintain, and match better with feeds and speeds manual machines short of really large, heavy, rigid machines offer.

 

[Moparmyway]

Had to go through this same exercise for my lathe. Once I got the shoulder cut on the faceplate, I transfer punched the faceplate and drilled & tapped the mounting holes. I had my doubts at the time, but my 4-jaw has worked just fine for me.
View attachment 347411 View attachment 347412 View attachment 347413

Why not mount the rear plate to the lathe directly ?

IMHO, if your chuck isn’t dead nutz, you’re going to be machining in that slop.

Mount the rear plate like it has the chuck on it, then you’re eliminating the variables, and face cut it that way.

 

[farminkarman]

Why not mount the rear plate to the lathe directly ?

IMHO, if your chuck isn’t dead nutz, you’re going to be machining in that slop.

Mount the rear plate like it has the chuck on it, then you’re eliminating the variables, and face cut it that way.

With a 4-Jaw independent chuck, it really doesn’t matter as you are having to dial in every workpiece. FWIW, my 4-jaw has less than .0005” runout as I did it.

 

[NPKenny]

Why not mount the rear plate to the lathe directly ?

That’s what I did. Got this far and have been out of town. I have a lot of simple things to do much differently for my next cut… like rotate my tool holder to clear the work piece. If you’re wise, you’re not ignorant for long. I’m glad to have finally made a cut and I have a lot to learn.

 

[NPKenny]

I tipped into an unexpected challenge. I can’t line-up threaded holes. I indexed the center ring and surfaced the face. I thought I was doing just fine until I drilled and tapped the holes… Only one of my holes fits cleanly. Two are useable. One is out by 1/4”.

I’m going to rotate the plate and try again. Any good tips to make sure I can properly drill and tap these holes?

My drill press method is hokey. Not good enough for the tolerances necessary.

I should also index the locating ring deeper

 

[SimonHS]

Did you use a transfer punch to locate the holes?

 

[mettee]

I need a lathe...

...and a mill.

 

[Moparmyway]

Do each hole one at a time

Drill
Tap
Bolt together
Drill
Tap
Bolt together
Drill
Tap
Bolt together
Last hole

 

[NPKenny]

Did you use a transfer punch to locate the holes?
[/MEDIA]

No!!! I punched through the chuck holes with a drift punch. Looks like I need to upgrade my method. Thank you.

 

[NPKenny]

Do each hole one at a time

Excellent!