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Four Jaw chuck

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Vic23/02/2020 18:32:18
3074 forum posts
8 photos

Is not my favourite work holding device but sometimes needs to be used. I often find it such a PITA to set up and today was no different. As the part to be re machined had a hole in it already I hung the work on a suitable rod held in a drill chuck in the tailstock and then carefully tightened the jaws of the four jaw. This got me much closer than I had been and within ten minutes of tweaking I lucked out when the DTI read 0.02mm TIR. As the part was not too critical I accepted this and machined the part. I couldn’t help thinking though, would you four jaw experts out there have generally accepted 0.02mm or would you have tried to get as near to zero as possible?

Emgee23/02/2020 18:42:04
2426 forum posts
290 photos

If the accuracy required is fulfilled it must be a good job, no point in chasing NASA tolerances.


pgk pgk23/02/2020 18:46:39
2563 forum posts
293 photos

I'm no 4-jaw expert but my accuracy would depend on the part and job - no point chasing unnecessary microns for the sake of it.
Having said that if the part was a decent shape as opposed to some weird irregular pentagon then i quite enjoy getting the 4-jaw close and 10 mins seems quite a long time so worth reviewing some of the tips on the subject - such as taping pieces of flat scrap to a rectangular bar and indicating on the inside of the overhang as being quicker than having to keep pulling the dti jaws back to get around external corners. Or indeed indicating on a rod in that hole if needs to be central.


Former Member23/02/2020 19:27:03
1329 forum posts

[This posting has been removed]

Clive Brown 123/02/2020 19:48:20
826 forum posts
41 photos

Some while back, following a tip on this forum, I made a 2nd key for my 4-jaw, a simple, short affair out of mild steel. This enables 2 opposing jaws to be adjusted in conjunction with each other. It's amazing how this speeds and eases the job of accurately centering a workpiece. Wish I'd made it years ago.

Former Member23/02/2020 19:57:31
1329 forum posts

[This posting has been removed]

old mart23/02/2020 20:39:02
3775 forum posts
233 photos

I have been meaning to make two extra keys for the 6" and 160mm four jaw chucks for some time, having often heard of the improvement in dialing in. It pays to practice getting a four jaw chuck spot on, the work is held more securely, especially when parting off.

As for accuracy in setting up, it always depends, although, more than once, halfway through machining something, I have kicked myself for not getting the first chucking spot on when I had the chance.

Edited By old mart on 23/02/2020 20:43:20

JC5423/02/2020 20:51:07
151 forum posts
14 photos

+1 for two chuck keys. John

old mart23/02/2020 21:32:26
3775 forum posts
233 photos

I usually sit the dti on the cross slide if it needs to be moved about when setting up, and moving the saddle and cross slide speed up the rough adjustments, otherwise it sits on the bed.

Martin Hamilton 123/02/2020 23:18:19
187 forum posts

If you go to Youtube & put in centering a 4 jaw chuck, there are some great very fast & accurate ways of centering a 4 jaw very quickly. I use these methods all the time now.

Hopper23/02/2020 23:54:07
6404 forum posts
334 photos

The key (pun absolutely intended!) to using a four jaw chuck is to be super-methodical.

Use the dial indicator to measure runout and also use the dial indicator to measure exactly how much you are moving the job at each adjustment. It should be exactly half of the runout.

For the last thou or two (.02mm or two) you can get the desired movement by tightening the jaw on the high side without needing to loosen the jaw on the other side first. A surprising amount of movement occurs this way.

With a bit of practice you will be able to get things running true within a thou"/.02mm in about three adjustments.

thaiguzzi24/02/2020 04:03:01
704 forum posts
131 photos

World 4 Jaw Championship.

Watch Keith Fenner vs Adam Booth, true 4 jaw artists.

Vic24/02/2020 11:15:12
3074 forum posts
8 photos

Ok, it seems like I have another job on the list - make a second chuck key!
What do most of you prefer for clocking the piece, DTI or Dial gauge?

Martin Kyte24/02/2020 11:32:30
2755 forum posts
48 photos

One of my most used 'tools' is a sprung (spring?) centre which makes setting up to a centre pop/centre hole very straight forward in the 4 Jaw. Easy to make too. I also have a dial guage that lives in a QC tool holder which also saves faffing around. Never bothered with a second chuck key.

regards Martin.

JA24/02/2020 11:51:19
1359 forum posts
80 photos
Posted by Martin Kyte on 24/02/2020 11:32:30:

One of my most used 'tools' is a sprung (spring?) centre which makes setting up to a centre pop/centre hole very straight forward in the 4 Jaw. Easy to make too. I also have a dial guage that lives in a QC tool holder which also saves faffing around. Never bothered with a second chuck key.

regards Martin.

Matches my set-up except that the dial gauge still lives in its box. However its mounting has had its own QC tool holder for over ten years.


old mart24/02/2020 16:26:54
3775 forum posts
233 photos

I prefer to use a lever type indicator rather than a plunger. If the stock is square or rectangular, I just use the tool to touch the corners and see the marks made, or the gaps left.

Martin of Wick24/02/2020 16:44:57
249 forum posts
5 photos

Centring work close to the chuck at a half a thou is straightforward. The real fun starts when you have a slightly longer piece that needs to be set concentrically at both ends.

That when you find out how good your chuck is or how much patience you have!


Edited By Martin of Wick on 24/02/2020 16:46:31

larry phelan 125/02/2020 16:10:05
1180 forum posts
15 photos

Never bothered much with the 4 jaw until I had to, then I began to see its real value.

Now I use it almost all the time, no real trouble to set up and much better results than the 3 jaw, none of which are dead on.

Howard Lewis25/02/2020 16:59:41
6113 forum posts
14 photos

An extremely useful accessory for a lathe, or rotary table.

Allows you to provide better concentricity than a 3 jaw, or allows work to be done deliberately off centre.

No end of uses to which it can be put inn the workshop.


Andy_C25/02/2020 17:18:44
47 forum posts
10 photos

A really good article on setting up a 4 Jaw Chuck is in MEW Mar 2016 pages 68-69. To get better than a few hundredths probably requires a second go around but it is a methodical method that might suit and once used to it is quick and effective.

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