By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Jan 24th

Easy method of 4 jaw centering

All Topics | Latest Posts

Search for:  in Thread Title in  
jon hill 301/09/2020 11:13:58
106 forum posts
18 photos

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

Ady101/09/2020 11:16:40
avatar
4728 forum posts
714 photos

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

roy entwistle01/09/2020 11:16:53
1408 forum posts

Use two chuck keys on opposite jaws

IanT01/09/2020 11:17:24
1895 forum posts
184 photos

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

Regards,

IanT

Pump valve body.jpg

br01/09/2020 11:21:47
697 forum posts
3 photos

Youtube.com ----- Dialing in a 4-jaw Lathe Chuck

jon hill 301/09/2020 11:25:45
106 forum posts
18 photos

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.

Mick B101/09/2020 11:30:07
2018 forum posts
116 photos

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.

SillyOldDuffer01/09/2020 11:42:53
Moderator
7550 forum posts
1680 photos
Posted by roy entwistle on 01/09/2020 11:16:53:

Use two chuck keys on opposite jaws

+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

Hopper01/09/2020 11:47:04
avatar
5505 forum posts
137 photos

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

Alan Johnson 701/09/2020 12:34:31
106 forum posts
16 photos

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."

Gary Wooding01/09/2020 12:56:34
872 forum posts
227 photos

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.

Tony Pratt 101/09/2020 13:05:44
1692 forum posts
8 photos

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

Tony

not done it yet01/09/2020 14:04:17
6325 forum posts
20 photos

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🙂 ).

duncan webster01/09/2020 14:21:45
3509 forum posts
63 photos
Posted by IanT on 01/09/2020 11:17:24:

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

Regards,

IanT

Pump valve body.jpg

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

Howard Lewis01/09/2020 14:30:46
5299 forum posts
13 photos

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

SillyOldDuffer01/09/2020 15:29:57
Moderator
7550 forum posts
1680 photos
Posted by Hopper on 01/09/2020 11:47:04:

... 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.
...

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

Gary Wooding01/09/2020 16:21:30
872 forum posts
227 photos
Posted by SillyOldDuffer on 01/09/2020 15:29:57:

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.

mechman4801/09/2020 17:23:30
avatar
2933 forum posts
460 photos
Posted by IanT on 01/09/2020 11:17:24:

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

Regards,

IanT

Pump valve body.jpg

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

George.

Hopper01/09/2020 22:55:40
avatar
5505 forum posts
137 photos
Posted by Gary Wooding on 01/09/2020 16:21:30:
Posted by SillyOldDuffer on 01/09/2020 15:29:57:

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.

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.

peak402/09/2020 00:10:04
avatar
1487 forum posts
162 photos

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

Bill

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
cowells
JD Metals
BOLDON
Eccentric July 5 2018
walker midge
rapid Direct
emcomachinetools
Warco
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest