Vic,

It is easier if you work in just one direction, say towards yourself, Slacken jaws where the job is too far from you and tighten those opposite to push the work your way. Use a DTI on a true surface as the errors get less and you will find that method works evert time. Final adjustments will be to chase thous by tightening the jaw need to move the work by that degree of error.

Regards Brian

Sometimes you can use the tailstock chuck to hold the part on a suitable spigot to bring it up to the 4-jaw and carefully tighten the jaws. That way you'll get near very quickly.

If it's an odd-shaped or large part you're stuffed with that idea! A clock gauge is good to get the thing sorted as you want it. As Brian says, use one position for the clock gauge and adjust things at that position. Measure how much eccentricity you've got at each jaw position and take out half of it as measured on the clock gauge. Obviously you have to work out which way the jaw needs to move…

No clock gauge? You'll have to rely on some kind of not-quite-sharp pointer held in the toolpost plus some feeler gauges to get it accurate. Again, try it at one position, trap a feeler in place between the job and pointer, and then use a half-thickness feeler and without toving the pointer, move the job until it's trapped between pointer and job.

You mention two chuck keys. Excellent method; I made a very small one (about the size of those tiny Jacobs chuck ones) that can fit behind or underneath the chuck so I can turn two jaws at once. You have to be careful that the job doesn't fall out whilst you're doing this, he said, having been there and done that. (Bring up the tailstock to keep it in place.)

Quick way for the inexperienced to get close is to mount a "probe block" in the toolpost and use the cross slide dial to calibrate the adjustment. Not something to keep doing forever but its a solid training method to get the technique nailed, the "feel" established and the WTHIGO thing sorted.

Actually easier if you start off visibly out.

Process:-

1) Pick one pair of jaws and spin the work so that pair of jaws is horizontal with the work error towards you.

2) Run the cross slide forwards until the probe bar touches the work making sure the contact area includes the centre line.

3) Zero the dial.

4) Spin work 180° so the error is away from you.

5) Run the cross slide forward till the probe bar contacts and note reading.

6) Pull back cross slide then move forwards until it reads half the error.

7) Adjust chuck until work contacts the probe bar.

8) Repeat with other pair of jaws.

9) Set up indicator and finally dial in using the same process. The indicator provides calibration so its much easier.

Remember that the upright chuck jaws only need to be tight enough to stabilise the job. It has to slide without marking.

Verdict lever type indicator sets have a nice bar and upright post device for toolpost mounting. Ideal for this process. Use the bar as the probe then mount the indicator to finish off.

Using the bar as a probe and cross slide as a claibration device makes things nice and solid so its easy to get used to the process.

After about 5 goes or so most folk have the knack sorted and outgrow that process.

I reckon to get close enough to put the Verdict up by simply looking at the jaw positions in relation to the scribed circles. Three turns round and I'm done to tenths thou.

If its a ruff job eyeing up against a tool will get me into the 3 or 4 thou TIR region.

Clive

I agree with 'practice, practice, practice', but I do find that a second chuck key makes it even simpler – and it's easy enough to make one.

Me too. Also, important to keep practising! I don't use a 4-jaw all that often and find my alignment skills wane after a few months. After a long delay I'm not surprised to take 5 minutes, but if I have several practice runs I get much faster again. Losing the skill means I'm still learning. I've thought of leaving the 4-jaw on permanently because a few weeks of having to keep at it would drive the lesson home! But 3-jaws are so quick and easy…

Dave

Do you honestly begrudge that 5 or 10 mins? if so practice practice practice

I keep a small clock on a Quick Change toolholder and use a second smaller chuck key on the back.
Pick a pair of jaws, set them horizontal, measure the offset on the clock and then push the workpiece towards you by half the offset. Repeat for the other pair of jaws; it really doesn't take long, and neither did making a small chuck key.

That's all very well for round bar, or a circular hole in the end of a workpiece.
This is a really neat way for centring square (or oblong) stock/

Bill

If you methodically use the following method, you can get it within a thou or so every time within one revolution of the chuck after the initial revolution to take the starting reading, so about a minute or two total.

Chuck up your round bar as best you can by eye, using the concentric grooves on the chuck face as reference. (Or use the toolbit or toolpost almost against the job as a reference if preferred.)

Set a dial indicator horizontally to bear on the job.

Spin the chuck by hand until the needle is at the lowest point and set the bezel to 0 there.

Spin chuck to the highest needle reading and note the reading.

Spin the chuck until the needle reads half this amount and then reset the 0 to the needle.

Now you can go around with your pair of small chuck keys, or "twiddlers" and set each jaw pair so the dial needle reads 0. Usually one go-around is enough to be within a thou or so. A second go around all four jaws will get it well within a thou if desired.

Once you try this and see how simple and effective it is, you will never go back to any other method. It literally takes one or two minutes to get the job running within a thou. I had done it by the usual slow old "trial and error" method with a dial indicator all my life until I read this method in a one-page MEW article by a Scandinavian chap whose name eludes me. It was a revelation in its simplicity and effectiveness. I can't recommend it enough.

Note: You can often get that last thou of adjustment by tightening the jaw on the "high" side without bothering to loosen the opposing jaw first. Seems to be able to move the job a thou or so most times.

Edited By Hopper on 21/10/2022 04:53:46

Hopper

That's what I do except I use a lever type indicator.

Always a little wary of the bend risk when spinning something against the long, slender, probe of a dial type. One reason why the Starrett "Last Word" is the inherently stiifer and stronger back plunger type.

If using a standard plunger type with domed end probe there is a potential issue with the probe contacting the work either above or below the centre line. Inspector Meticulous can work out how much!

Some folk like to put a block on the lathe bed to support the nearest chuck jaw exactly horizontal. Its calimed to make it easier to keep things in place when twiddling the adjusters giving a more stable indicator reason.

Until the internet arrived I wasn't aware there were so many idiot stupid "claimed best(!!)" ways of lining up work in a four jaw.

Using cross slide dial and block probe was the way I was first shown. Partly because its a good training method that doesn't risk neophyte clumsiness damaging a indicator and partly because I din't have an indicator at home anyway. Just a Unique. Uber cheap, far more effective than it ought to have been, but only about 5 thou useful range so I needed to be close before it could be used. Mr Portass didn't put dials on the S type which made things even more interesting.

Clive

Sometimes, it is quicker with 2 DTI and 2 keys. Sometimes its easier to have a stubby length key for the under side and the std key for the top. Some lathes do not allow the ability to use 2 keys front and back at about the same time.

Double post. Apologies

Howard

Edited By Howard Lewis on 21/10/2022 11:22:29

This is the exact method I use. I’m no machinist, but can often get things centred to within half a thou in one go, mostly two though.

With two chuck keys, it’s a doddle, and with my NOGA dti stand with fine adjustment *at the base*, I actually find the process quite therapeutic (the base mounted fine adjuster makes zeroing the dti laughably easy because you don’t actually touch it or the arm, therefore there’s no spring back).