Centering square stock in the 4-jaw

I'm doing this by adjusting the chuck until a cutting tool nicks/touches the corners of the (as rolled) bar more or less evenly. That's OK for for the job in hand, but it made me wonder if there's a "proper" method for doing this.

Rob.

After approximately centring using the method you describe, you can either use a dial gauge with a flat foot to clock the corners, or the same but with a standard tip to clock the flats. In each case you obviously have to be careful not to wreck the gauge - manually lifting the tip away from the work as you turn it into position.

Start with one pair of opposite corners (or flats) first, and when they’re ok move on to the remaining two opposites. Much quicker to do than to describe.

The "proper" method is whatever works for you. I generally do as you do, and with the addition of a dial indicator if needed for fancy work as above.

But another way is to use a piece of round bar the same diameter as the across the flats measurement of the square bar. Put round bar in the chuck and set it true using dial indicator. Then loosen two jaws of the chuck, pull out the round bar and slide in the square bar. Now tighten those same two jaws and the bar should be set true.

I have on occasions used the 'cheats' method of drilling out a piece of round bar until the square stock is a snug fit, then slit one side of the round bar and hold the lot in a 3-jaw. OK for quick & dirty but might not be up to scratch for something needing more finesse, but if you are using hot-rolled square bar then there's no guarantee that it is in fact square.....

Hi Rob,

If you find the centre of the square using a height gauge (or scribing diagonals if you don't have a height gauge) and centrepunch it you can centre it in the chuck using a wobbler.

Regards,

Alan

I saw a chap on utube (  forget who ) put a piece of flat material on each face of the square stock and secured with a strong rubber band and use a dial indicator on inside faces to centre stock

Mick

+1 on the rubber band and old gauge blocks trick. For sizes under 3/4" I use 5C square collets as they are a time saver.

Obviously start by rough aligned using the lines on the four jaw face. A bit of low cunning with a depth micrometer or the probe on a vernier / dial/ digital caliper on the outside of the jaws can help get it a bit better.

Put a suitably hefty bar with the end accurately perpendicular to the axis or similarly accurate and decently rigid L shape in the tool post to act as a setter reference. Something around 1" x 1" bar or 1" wide L will do. Run it up until it contacts the side of the square being centred. Lightly rotate the chuck bar and forth so the contact is true to the side. Note cross slide dial reading or zero dial. Retract setter, flip 180° and note dial reading. Re-set cross slide to halve the difference, remember backlash, and adjust four jaw to bring the square bar up to the setter. Flip 180° and check dial reading should be close. Repeat on the other sides. Go round again if need be. Quite possible to get a thou or less TIR.

Best to have a cross-slide stop when using a dial gauge so you can withdraw the cross-slide to get the gauge safely out of the way before rotating to the next side and go back to same position. One day you will forget. Even if its a fancy one with locking retract lever, mine would have been mega expensive at list price!

Make a note of the TPI or pitch of your jaw adjuster screws. Gives you a good idea of how much to turn them when adjusting. If you don't do a lot of four jaw work you loose the feel for how much a fraction of a turn shift things.

Clive.

That would be Joe Pieczynsky. Worth chasing down the video, it and many more like it have innovative and usually simple solutions to these problems. Some of his ideas are so elegant I can't imagine why I wasn't taught them at school.

Rgds Simon

Or if you don't need micron accuracy... scribe an x on the end, centre pop it and set it true to a dead centre in the tailstock. More accurate than using the corners if they are a bit rounded.

Or cheat and get an SC 4-jaw

Neil

Edited By Neil Wyatt on 20/10/2017 09:38:17

As Neil says - mark out (preferably with a vernier height gauge), carefully centre punch and then centre in the four jaw using the lathes centres (but using two like this)....

Regards,

IanT

(PS - Part shown isn't square but the principle is the same)

Edited By IanT on 20/10/2017 10:10:28

Here's the link to Joe Pieczynskys video:-

**LINK**

Nick.

Now having the digital magazine and reading it on night work, I found this explained in a back issue, long time back in the early nineties. Several ideas came up, but one I remember was that a hight gauge was put on the cross slide with the correct hight worked out. I must say I don't do much on nights now I have the archive mag and has past the time so far this week.

Two more tips that may help.

Make a solid setting bar to sit on the lathe bed of exactly the right length to put a jaw pair horizontal when one is butted up against the top of the bar.

Setting with a gauge goes faster if you have two keys in opposing jaw adjusters so you can push both ways. Short key with stubby arms or knurled knob is more convenient when adjusting than the full fat tighten to grip version.

Clive.

Use 2 keys with your 4 jaw chuck and they become very quick to use. For and Aft or on a diagonal like when using a myford. My second key is just a piece of key steel made to fit the chuck with about a 38mm -1-1/2 inch disc attached.I use 2 of these, and the final tightening is just with one key that came with the chuck.

Thanks for replies chaps, I was hoping there was some trick I'd not heard or thought of which would give me a Doh! moment, but it seems not. Indicating off the faces is tricky for me because I always manage to turn the chuck a little when doing the 'opposed keys' thing, and that fouls it up. I'll try to find flat anvils for my dial indicators so I can go off the corners more easily. Something I have learned from this job is to spot a centre on the end of the bar when, by some miracle, I've got it right. Then, when I realise it's got to go back in the chuck because I didn't think of something, it's much easier.

For some reason the easing off two jaws at 90 degrees, removing the work and replacing it tightening only the same jaws thing has never worked for me. Never in the same place precisely! Perhaps I need more practice with the 4-jaw.

Thanks again for suggestions, Rob

Robin

One advantage of the hefty bar or L shape setter technique described in my first post is that bringing the setting piece up against the side of the bar pushes it back to perpendicular if you have rotated things a touch.

Bar under a jaw as mentioned in my second post is also pretty effective at keeping things square. Just hold the chuck jaw down onto it to keep it horizontal.

In my view routinely using a dial gauge on square stock is asking for trouble. Bound to forget about moving it out of the way one day. Usually when being frustrated by that bit of stock which refuses to come back dead right. Nearly but not quite.

Needs a decent chuck and educated feel for the loosen two jaws and replace approach to work really well. Wasn't until I got my Heavy 10 that I had a chuck good enough to really behave.

Clive.

Partly technique, but swarf in the chuck messed me up good and proper. Taking the jaws out and giving them and the worms a careful clean made a surprising difference.

Dave

Clive - I didn't read your first reply attentively enough. Sorry! Revisiting I see better how that works - as I have to set a square bar many more times to finish this job, it'll probably be worth the overhead of making the device. As I have the luxury of DRO's it makes even more sense, don't have to worry about backlash too much.

Dave - thanks for the tip about swarf in the works. I'll give the 4-jaw a good clean and see if it improves things. I might just leave the 4-jaw on the lathe for a while to force me to get more skilled with it. The damned thing weighs upward of 20kg, so I don't look forward to shifting it on and off.

Rob.

Edited By Robin Graham on 23/10/2017 00:13:11

Robin

Let us know how you get on. Maybe write it up for Neil. I centre square stock up about once every third blue moon so never really sorted the best method out. As my Dickson is always set square to the bed I just use an empty toolholder. Front of the back is vertical for all practical purposes and the jaw usually slips into the slot space.

If you are using small stock, say 1/4" or less, its probably better to use a block under a jaw as mentioned in my second post to get the face of the stock truly vertical. Simply pushing with the setter risks bending it a touch and it will be harder to feel true vertical.

Just occurred to me that the idea works just as well with round stock. Especially if you have a DRO.

Clive.