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

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.

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

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.

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.

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

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

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

The Toolmex 6" four jaw I have fits easily on the 6" rotary table, especially as there are four slots.

To indicate stock accurately with the 4 jaw chuck, I like to use Aluminium or brass pads ,between the jaws and the work piece. These do 2 things, prevents damage to the work piece, and allows an area to squash up a little to allow you to get the very last little bit out of the alignment of the part. In general it should be quite easy to get a part indicated to 1 thou , especially when you pre dial with 2 short keys. Then use the main key for the final micro adjustment. Realise that some jobs , just require light cuts to get the best results over all.

Sometimes using 2 dial indicators can make the setting up of a part much quicker.

Neil