4 jaw independant chuck help

[Nozzle]

hi everyone!

im new to woodturning and have recently bought a 4 jaw independant chuck but i cant seem to get the nack of centering a piece.
Ive used the chuck on 1 peice of turning which was my first bowl attempt, i first used a paceplate to turn the base of the bowl and to which i turned a tenon. the bowl blank was not trued up before i did so then i turned the tenon.

i then carefully measured and used dividers/callipers to make it central only to find out that its not central when i go to turn the insed of the bowl.

i was just wondering if there is anyone out there any good tips/advice that could help me.
At the moment i cant affors a self centering chuck although it is on my list of things to get.

thanks for your time.
(sorry for long post)

 

[DTR]

I don't know what the preferred method for wood turners is, but for metal turning you'd use a Dial Indicator. Movement of the plunger gives you a deflection on the dial. You'd mount the dial indicator on a stand, usually magentic, and mount it so the plunger is sitting on the workpiece with about half deflection. Rotate the chuck by hand and you'll see the dial deflect. Use this as a guide and correct the chuck's centering, improving as you go.

No doubt someone will be along shortly to describe that much better than I did

 

[CHJ]

Heres a PDF link from my web site that describes in detail the method that Dave refers to.
Hardly practical for wood turning though as the wood will naturally be distorted as soon as it's cut more than the sort of tolerances discussed.

Further more, holding a wooden piece in an engineering chuck is not advisable as the grip will not be secure enough.

A wood turning self centering scroll chuck is fitted with either dovetail jaws or special serrated jaws to accommodate wood compression and prevent disengagement. Holding a plain spigot or socket in metal turning jaws will inevitably result in the wood compressing due to the small contact area and the piece working loose out of the jaws.

 

[Paul Hannaby]

How about using a pencil? once you have the bowl roughly centred in the chuck, rotate it slowly by hand while holding a pencil on the toolrest so it just touches the bowl at the nearest point. This will show which side is farthest out so loosen the opposite jaw slightly and tighten the nearest a little then repeat until you have it close enough.
I would agree with what Chas says about having jaws that give enough grip.

 

[jasonB]

This is the method I use for irregular shaped items to get the centre point lined up which you are quite likely to get on the wood lathe if its a bandsawn blank. Not my pic but the way I do it.

http://picasaweb.google.com/Tug423/RW29 ... 9500816850

J