Four Jaw chuck

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?

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

Emgee

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.

pgk

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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.

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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

+1 for two chuck keys. John

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.

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.

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.

World 4 Jaw Championship.

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

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?

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.

JA

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.

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

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.

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.

Howard

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.