Two chucks one back plate.

[dobbslc]

I have a lathe chuck question here as I'm struggling to fit the 4 jaw chuck to my lathe. I've had the lathe for a few years but never had the 4 jaw on it, when I try to fit it the mounting holes don't quite line up!
Do I need a back plate for each chuck or should they both fit the one fitted to the lathe?
Here's some photos.

The 4 jaw is on the right.
And the face plate.


I've just noticed that one of the threads in the 4 jaw isn't square
It looks new and unused.
Any tips?

 

[Milkybars]

I would doubt that they both would work with the same backing plate.
The recess in each chuck at the back should be a very nice fit over the raised ring of the back plate and then it's bolted home

 

[Richiew]

You really need a backplate for each chuck. You don't want to be swapping back plates each time. What lathe have you got? You can pick up a machined back plate pretty cheaply if it is a common lathe. You just need to turn the register.

 

[brightspark]

wouldn't be worth the hassle changing them get another backplate

 

[God mode restorations]

Backplate for each chuck. Once the backplate is fixed and dialed in to the chuck the last thing you want to do is remove it.

 

[dobbslc]

New back plate it is then!
It seems the 'new' 4 jaw is a bit crap as more than one of the threads are on the ****! Can o get a chuck and back plate together?
It's a Chester lathe / mill so a Chinese one.
Here's thy beastie.

 

[dobbslc]

Backplate for each chuck. Once the backplate is fixed and dialed in to the chuck the last thing you want to do is remove it.

Err opps! Already taken the 3 jaw off!

 

[Richiew]

What thread is it?

 

[dobbslc]

Good question! I don't even know how to take the chuck off.

 

[dobbslc]

I mean it's a R/H thread but I can't see how to lock the spindle.

 

[Agroshield]

Do you have the manual for it?

Chester only sell two three-in-one machines, so I have only a 50% chance of linking the wrong one:

https://cdn.shopify.com/s/files/1/0011/7558/4815/files/Centurion_Instruction_Manual.pdf?539

Your spindle does not have an unscrewable backplate (page 17). What you show in your photo is what you get. Any more will require an 18tpi 12" Bahco spanner. This is quite common on the mini-lathes as well.

The four jaw chuck seems to have a series of holes around its perimeter (so it will fit many different machines). Have you tried all possible combinations of three hole patterns to see if it makes any improvement?

Do two of the bolts line up and just the skewed one not fitting? If so, you can turn down the shank of that bolt to give clearance, but leaving the threads that go into the chuck (so it would be an 8mm shaft with M10 threads on the end). You would have to insert that bolt first and wind it into the chuck as you go when installing the chuck.

If real bad alignment, use studs and nuts to secure the chuck. M10 thread on end, green loctited into the chuck, 8mm the rest of the stud. Good thick washer. Radius the transition between 8mm and 10mm to stop stress risers.

 

[optima21]

yeah in most cases a separate backplate is required for each chuck, but I decided to have one backplate for both the 4 jaw and 3 jaw chucks on my hobbymat. the reason I did this was because the backplate bolts to mandrel by 3 cap screws and I'd have to unbolt the chuck from the backplate and then unbolt the backplate from the mandrel.

the backplate was fitted to the 3 jaw chuck (when I made it) and then the recess in the 4 jaw was slightly enlarged to fit the backplate.

 

[dobbslc]

@Agroshield I do have the manual for it and hadn't checked to see what the parts diagram shows so thanks for the link. Mmm so no separate back plate then, that's probably why Chester don't seem to list them then!
Good job I didn't try to 'loosen' it!
I have tried all the different holes on the chuck but only one set are the right ones, it does look like that chuck has been made by a blind Chinaman drunk on rice wine or something as a few of the threads don't look right!
I'll try the reduced shank on a bolt to see it that helps, thanks for that tip!
I really should treat myself to a nice Atlas or Holbrook lathe but can't do that right now

 

[Pete.]

Why not get/make a backplate then offer it up to the back of the chuck and drill new (straight) holes. There's no reason why you have to use the originals.

 

[Agroshield]

Why not get/make a backplate then offer it up to the back of the chuck and drill new (straight) holes.

And if the 3-jaw fits well, you can use the Doubleboost paper and grubby finger method to make the template.

 

[Arc Tourist]

You can not guarantee accurate work with a self centering chuck (3 jaw) by swapping its backplate back and forth with other chucks. Not a problem for four jaw chucks if the backing plate register closely fits, as the work can be centered with a dial indicator. Not so with a self centering chuck, as a small amount of play in the bolts can through it off centre a few thousandths or even more.

For precision work, ideally a three jaw chuck should have its own permanently attached backplate, and the jaws ground concentric with the spindle rotating so that accurate work can be done.
An additional backplate for your four jaw chuck is cheap insurance that your three jaw will not lose its accuracy, and well worth the small cost and the time saved in setups.

 

[dobbslc]

As @Agroshield says the backplate is part of the main spindle!
Here's a screen shot of the parts manual.

 

[Kram]

Appears your chucks are a direct fit on the spindle flange. The 4 jaw has 12 mounting holes, have you tried in all 4 sets? Unusual to not have a backplate, but in some ways better it wastes less bed length. 3 jaws are not the most accurate anyway -use for quick jobs that dont need to be remounted accurately!
Making a backplate is easy. Face a peice of bar and turn a bore to be an exact fit on the spindle register. Use transfer pins to mark the holes, drill and tap. Mount it to the spindle and put an alignment mark. Turn a register for chuck and use transfer screws to mark the holes. Drill and counterbore the spindle side.

Ive made 4 backplates for mine and shrunk fit bar to make collet chucks. The er40 chuck is the most useful thing I have made!

 

[dobbslc]

I've been making some parts for a mates Alfa suspension he's modifying



Just need the dimension off him so I can part it off.

 

[eLuSiVeMiTe]

Meh. Buy the biggest 4 jaw you can fit
Machine a register to fit the existing plate to the Chuck. clock the 3 jaw into the 4jaw as needed.