Easy method of 4 jaw centering

I am having great difficulty centering an independent 4 jaw chuck does anyone have any quick or fool proof methods?

I use the toolpost / side of the tool and finish with DTI

You can do the job 98% by eye

It's like sex

The more you do it the easier it gets

Use two chuck keys on opposite jaws

Depends on what kit you have to hand. I generally use two centres and a DTI

Regards,

IanT

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Thanks guys all useful tips, currently I just use a dti on say round bar.

I think I will make a new 2nd key as my next mini project.

If you can grip the piece in the drill chuck, offer it up from the tailstock end and carefully close the chuck jaws onto it. You should be within a few thou and well inside clock gauge territory by then.

+1

And practice!

I position the job roughly by eye, sometimes using a centre in the tailstock as a reference, sometimes with the lines on the chuck, at this stage not tightening the jaws.

Easiest and most accurate to measure offset with a DTI, but it can be done by eyeballing the gap between a cutter and job.

With two jaws horizontal, set the DTI. Then rotate through 180 degrees to measure the difference. Turn the keys in opposite directions to halve the difference, tighten one while slackening the other. Rotate back through 180 degrees, measure the new difference and halve again. Then set the other two jaws horizontal and centre them with the same process.

At this point, the job should be more-or-less accurately centred. Spin through a full turn to see how good or bad it is, and repeat the 'halve the DTI difference' with two chuck keys as necessary.

Tricky bits;

• During adjustment making the jaws tight enough to hold the job without being so tight as to make halving difficult.
• Learning to turn two chuck keys together and in the right direction! (I still get this wrong occasionally)
• Tightening up at the end without disturbing the centre setting.

I cracked it by spending a few hours doing nothing but centring various objects in my 4-jaw. Initially I had to think every move out, now it comes naturally.

Dave

Edited By SillyOldDuffer on 01/09/2020 11:44:34

Two chuck keys are good. Getting it roughly right by eye against the tool bit is good.

Then the easy way to finish off is this:

• Put dial indicator on the round bar and rotate the chuck once.
• Note the highest and lowest dial gauge readings.
• Set the 0 mark to exactly halfway between the two readings. (Rotate the job one more time to check you are now getting identical plus and minus runout readings.)
• Go around each jaw and set it so the dial gauge is reading 0 as each jaw is next to the dial gauge.
• When the reading next to all four jaws is 0, the job is trued.

I did it the old, hard, trial-and-error dial indicator way for 40 years before discovering this so-simple no-brainer quick method. Hope you are smarter than I was. The simplicity and effectiveness of this method still leaves me gobsmacked.

Edited By Hopper on 01/09/2020 11:51:05

Edited By Hopper on 01/09/2020 12:04:08

By eye - use the tool or tool holder to give you an indication. Then, digital DTI. It is easy (if you have one). Set to zero at jaw 1, rotate to jaw 3. DTI will give you a + or - error. Halve it, and adjust jaws to correct. Likewise jaw 2 and 4.

Practice on a bit of round bar first. As others have said "prctice makes perfect."

I use a method which is very quick and accurate, but not, it would seem, very well known.

***THIS*** PDF explains the method.

Although not absolutely necessary, the use of two chuck keys makes life much easier.

Never felt the need for 2 chuck keys & lots of practice works wonders.

Tony

If it is smallish round bar, you need to get it fairly close before tightening anything. Otherwise, if two jaws are OK and you are trying to adjust the other pair, the tight jaws may prevent the bar from moving as you might expect it to - due to trying to force a larger diameter through the already tight pair of jaws.

Quite often, I don’t bother to change from a 4 jaw independent chuck to a self-centring one unless for a better reason than centring the odd new workpiece (I might if I was using smaller chucks than 160mm🙂 ).

Instead of 2 centres I have a bit of 3/16" rod about 12" long with a point on one end. Grip the non pointy end in the drill chuck in the tailstock and apply DTI towards the pointy end. Saves swapping from chuck to centre. One of these days I'll get round to loctiting a bit of bigger stuff to the non pointy end so that the DTI can be applied when the eccentricity is higher. I'll put a flat on it so it doesn't roll off the shelf, but not run the DTI on the flat.

When applying it to the centre pop, I wind the tailstock out until the handle is at the back before locking the tailstock, The weight of the handle then keeps the point in the mark

Like IanT I use two centres, and a finger clock as the job comes nearer to being centred.

This is extremely helpful where the job is either deliberately eccentric, or irregular in shape.

I made a second key for the "baxk" jaw, but very rarely use it.

Practice makes perfect. the more that you do it, the easier and quicker it becomes to centre work.

Howard

Just tried Hopper's method only to find it took longer. Despite understanding the logic I slowed down just because the method is slightly different from what I'm used to. Hard to break old habits I guess. I shall persist : Hopper's way must be easier!

Dave

It is - it's the same way as described in my link.

This is also my preferred method, have also used the two chuck keys method.I find this one the easiest.

George.

It's not my way. I saw it published in MEW about 2 or 3 years ago. Can't remember the author's name. A Scandinavian chap maybe. He described it more clearly with illustrations.

Here we have quite neat way of centring square bar in a 4 jaw.

Bill