Runout on chuck.

I suddenly seem to have 0.06mm runout on my 3 jaw chuck. The back plate measures 0.02 out, the far end of the chuck 0.06 out and anything more than 2" length from the chuck is 0.4mm out!

It was fine last time I used it and it's not been taken off the lathe!

I've checked the runout on the L00 lathe spindle and it's 0.001mm, there doesn't seem to be anything wrong with the spindle or chuck fittings and I've tried varying the bolt tightness from the chuck to back plate.

Any ideas?!

Edited By Chris123 on 09/12/2013 00:12:50

Edited By Chris123 on 09/12/2013 00:18:51

If there's truly nothing wrong with the backplate/spindle side of things, it suggests there may be a problem with one or more jaws. I presume it's a scroll chuck so perhaps something going on between the scroll and one of the jaws.

I think the first thing I'd do - it's easy anyway - is take the jaws out,clean everything in sight and inspect for damage.

0.06mm or 2 1/2 thou runout on a 3 jaw chuck does not seem excessive to me.

I'm curious as to what sort of equipment you have that can measure a run out of 0.001mm or 1 micron?

Edited By Paul Barrett on 09/12/2013 03:20:49

Hi, I cleaned the scroll and the jaws first and it made no difference. I'm fairly sure the runout on the chuck body used to be 0.02mm, and the backplate <0.01mm.

Runout was measure with a normal dial gauge, spindle runout moved it approx. 10% between the 0.01mm graduations.

Hi Chris

It may seem a silly question, but how do you know it was O.K. last ttime you used it, did you clock everything? How old is the chuck? It appears from your description that it may be the bolting face of the backplate that is the problem .4 mm 2" from the chuck is excesive.

Chris, to add to my earlier reply, in over 50yrs I have never known a chuck to develop a serious run out of its own volition. Usually it has had some form of traumatic incident or has been removed and swarf has crept in somewhere. When you measure the bar held in the chuck, does the run out increase dramatically the further frm the chuck you get? The other thing is, the body of the chuck is possibly not concentric with the jaws anyway.Did you use ground bar for the check or just a length of drawn mild steel? Many will tell you that ground bar does not necessarily mean round but is a darn sight better than drawn mild steel. Is the backplate register and its mate, the chuck register a good fit?

Don't look for a 3jaw chuck to be supper accurate because it won't be and remember any run out shown on a clock is in fact double the actual run out. The other thing is you are dealing with a number of parts each with their own error. These can cancel each other out but sods law says the errors will compound and become a greater error.

Chris when you measured the "chuck runout" what exactly did you measure? If it was a bar inserted in the chuck, was it just as you tightened it, or did you take a cut first along the bar?

If as you say nothing had changed on the lathe/chuck since last time you used it, then frankly nothing will have changed with the run out. The lathe and chuck are after all simply inanimate objects.

When you say " the far end of the chuck is 0.06 out" are you clocking the chuck body itself?

No self centring chuck will hold a work piece that runs true initially. All that matters is whether it cuts round and parallel. Only measuring a work piece agter turning is relevant. Like Dusty says remember to that the total amount shown has to be halved to identify if you are cutting accurately. HTH.

My new WARCO also runs out around .0025" which annoys me as my old French mini lathe was good down to .0002". My annoyance stems from the fact that the new WARCO cost almost ten times as much as the Frenchman. >>

Putting things in perspective though, years back when I last worked in a tool room much of the stuff that was turned was destined for heat treatment and subsequent finish grinding so bits were usually made with + .010" grinding allowance so a bit of run out was neither here nor there.>>

My bet is that like me you'll learn to live with it.>>

Having read the thread I cast my mind back to what would have happened if any of us experiencing a similar problem had called for Ted the millwright to attend the patient. He was a dry old cockney with a deadpan delivery. Slouching down the gangway with his gawky apprentice he would arrive at his victim and without exception give the machine a massive welt with the hammer he always carried.>>

Ted reckoned that when he was doing his apprenticeship in the East End he once asked Ernie the millwright for advice on the best way to fix a faulty machine " 'it it wiv an 'ammer' " came the reply and Ted had obviously never forgotten what he considered was sound advice.>>

He made 'oi larf!>>

Rik>>

3 jaw chucks never run true through the opening range of the chuck. that's a fact, new, old, precision, Chinese or any where else.

If you need to run true from the bar stock use a collet or a 4 jaw chuck

Hi, yes the chuck body had 0.06mm variance on the dial gauge.

Strangely the next day I looked at it again, took everything apart and cleaned it and it's back to 'normal' now. The chuck body is now back to 0.02mm on the dial gauge.

The 0.4mm on the dial gauge was on a straight bar that I use to centre the tailstock, the further from the chuck the worse it got. This seems to be back to circa <0.05mm now.

Thnaks for for your help, out of interest what sort of runout do people get in a 3 jaw chuck?

Bit late but also remember that only one chuck key hole is considered to be "accurate", the master one, marked with a "O" or the one nearest the label.

chriStephens