anesthes

iTrader: (12)

My sister bought me a self centering chuck for my small lathe. (3" chuck). I've never had one, I've always used a 4 jaw and spent 10 minutes with a dial indicator centering my work.

Anyway, I've got this thing mounted on the lathe and it has around .030" runout!

I looked at the spec sheet, and it showed an A dimension (outisde of chuck), and B dimension (face of chuck) and both showed .030" on the diagram. I'm assuming this means it's got .030" of runout and that's to spec. (HOLY SH!!

This seems like a lot to me. Like. Any thing I make that has to be centric (pulley, etc) wouldn't fly.

Any thoughts?

-- Joe

LX_SS

Holy hell is right, that a metric **** ton of run out. 0.003 would be acceptable not 0.03 damn.
I'm guessing it uses a backing plate to mount not a set of cam bolts ?
Is it the same backing plate you use on the 4 jaw ?
Usually its the mounting of such that causes a big issue however if the spec sheet says its within tolerance, not sure how much better you will get it.
Anything you want super accurate as you said, 4 jaw and dial indicator is the way to go.

If it was purchased new from a store i'd return for a refund if its possible.

anesthes

iTrader: (12)

It uses a backing plate adapter. It screws onto my lathe (1/2-20). The hub on the backing plate was about .020" larger, so I turned it down until it was just right. In theory, this should perfectly center the chuck, it's got a nice tight fit into the hub. Then 3 bolts to lock it down.

I'm just somewhat annoyed.

-- Joe

LX_SS

Could be possible the surfaces of the new backing plate adapter or the chuck. Even the mounting holes of the chuck to the backing plate not being perfectly aligned.
Other option is it could be in the jaws themselves.
I haven't done it personally, but i have heard of others doing very small machining on the jaw teeth that are out to help get it to run true.

Yeah i can certainly agree with how annoyed you would be feeling.

Grant2k

I was thinking that grinding the teeth would be the way to go, but then if you ever remove the chuck you'd have to redo it every time. Could you get more faceplates and remove the faceplate from the threaded spindle every time? Get the chuck right and have a faceplate for every chuck. That would be the most accurate solution. Or get a chuck that threads right onto the spindle.

anesthes

iTrader: (12)

Faceplate?

-- Joe

Grant2k

Maybe faceplate is the wrong term, I'm not really familiar with small lathes like this. But I would guess the end of the spindle has a thread on it and on that thread is something like in the picture below. The most accurate, concentric, and repeatable way to mount and remount something on the spindle would be using those threads. If you can work it so that when you remove the chuck you are removing it right from the threads on the end of the spindle rather than with a pattern of bolts it would seem like you'd have less of a headache going between your 3 and 4 jaw chucks.

What I picture on the end of your spindle:


What your spindle probably looks like if you remove that plate:

anesthes

iTrader: (12)

Oh yeah, called a hub adapter when I ordered it but maybe faceplate is right .

The adapter was screwed onto the lathe, and the hub turned until it was the same diameter as the register on the new chuck.

What I did NOT do was turn the face, so maybe I can take 10 thou off the face and see what happens.

My 4 jaw has it's own adapter/faceplate.

Here is a picture to the spec sheet though..

-- Joe

RSD

When checking runout, did you check at say an 1" from the chuck and then 3" from the chuck? I cannot imagine any chuck having a spec of 0.030 runout.

anesthes

iTrader: (12)

The chuck itself is about .016", which is what the spec sheet says. (I posted the image).

When I put something in the chuck, about 4" out it's around .030".

When I put the same material in my 4 jaw chuck, I'm around .002-.003" runout...

-- Joe