How accurate is your lathe?

[ray jones 1Participant @rayjones1]

How accurate is your lathe?

I have a Myford 254+ , its had very, very little use.

Fitted with an original 3 jaw self centre chuck, using a test bar 1" OD ( or selection of,), using a fixed DTI, located 1 inch from the chuck jaws , when I rotate the chuck .I get a concentric error of 1 thou. Would you say this is normal, average.good or bad.

If I run the DTI on either the outer diameter of the chuck, or the front face of the chuck, the error is near to zero thanks.

[ray jones 1Participant @rayjones1]

[Michael GilliganParticipant @michaelgilligan61133]

Ray,

In a self-centering 3-Jaw Chuck … that sounds fine.

If you want better, you will need either an inedependent 4-Jaw, or Collets.

MichaelG.

[mgjParticipant @mgj]

I think I might remember the jaw/pinion number that produced that. A standard SC chuck in good nick by Pratt & Burnerd will only hold concentric to about 3 thou.

A Super Precision SC 3 jaw from Pratt will be under a thou one one jaw only, but with both sets of jaws. It will however vary pinion to pinion with diameter (according to the bit of paper it comes with), so to get the best out of it one needs those test results handy.

So one thou with an ordinary 3 jaw is pretty good. Might also be wise not to abuse it, thopugh up to a point the accuracy of the chuck is not relevant. If something has to be genuinely concentric than one will set up in a 4 jaw, or if using a 3 jaw, you'd turn to size Personally I'd never put something in either a 3 jaw, or even collets and assume it was true without clocking it. A Griptru is handy though. Its a bit quicker to adjust than a 4 jaw.. So on reflection, my super precion 6" for the big lathe was, in hindsight a waste of the extra dosh – it does have hardened slides, sure, but for amateurs like us thats hadly a consideration.

[MadMikeParticipant @madmike]

Ray I have a Myford 254S, one of the last refurb models they sold at the end of 2010 before they sold to RDG. Mine has the Camlock chuck fitting.

If you are clocking a test piece, of known size, held in the 3 jaw chuck the .001 seems OK to me. Did you turn the test piece and then clock it, or is it a test piece of known size etc. You should be able to turn a piece with 1" diameter OD more accurately than the result you have given.

When I set my 254S up I spent a long time levelling it etc (some will argue the need for this but it works for me) and turning the recommended Myford dumb bell test piece. This results in a degree of accurace much better than .001.

Clocking the faces of the chuck will prove nothing as they have been ground and will thus be more accurate.

Incidentally how do you get on with your 254. I have to say that I looked at anumber of machines of far easter origin before I came across the 254. It is certainly much more robust than the current crop of new machines.

[ray jones 1Participant @rayjones1]

hi

thank you for the replies.

I have only owned this 254 + for a few months.

I bought it off an old gent, who had it new direct from Myfords,

basically he hardly ever used it.

It runs very quiet and sweet, I like the variable speed a great deal.

I have owned numerous Myfords over the years , but not any variant of 254.

this 254 has the camlock fitting which is very useful.

I have never taken the chuck off this one before, and just by chance

put a DTI on after re fitting the chuck.

Whilst using the 254 you feel as if you are using a lathe of substantial quality

The motor is rated at 2hp. Having said that , is does not appear to have the power of other lathes

rated at 2hp . I have a Myford 280 which is also rate at 2hp. The 280 compared to the 254 is

much heavier constructed, substantially more robust in every way and has much more power , should you need it for a heavier cut..

The common problem wiith both of these lathes is parts, as you know Myford parts are now very

often difficult to obtain, very expensive and sometimes just impossible to locate,

especially for the 280..

thanks again

[mgjParticipant @mgj]

Are we sure we are not getting confused between repeatability/concenetricity of the chuck, and paralellism/leveling/lack of taper in the bed.

Surely, if you turn a bar in a lathe, even if it is held eccentrically, the result will be a dead true piece, radially, even if it is axially tapered. If then there is a detectable error that is not due to surface imperfections, there is likely to be a problem with bearings, looseness in slides, chuck gripping etc.

If the piece is truly round, but but tapered, then the dumb bell test (leveling, twist – call it what you will) hasn't been done properly, or there is some sort of fault in that direction.

But the two are not the same, and in general terms don't cross reference.

The whole drift of this thread has not in fact been about lathe accuracy, but chuck accuracy, which again, are not the same thing at all. For one to think that a 3 jaw is OK at .001 runout……. They are only built to about .003. You can get an ordinary 3 jaw which meets then normal DIN standard for a very reasonable price. A top grade 3 chuck guaranteed to hold to .001 or less is about £4-500 plus vat in our sizes, and going up, and it will stil only hold to that on one nominated master pinion. Unless one is lucky and you happen on a good one.

.001" when new is darned good for a slef centring 3 jaw. No one ever bought an SC three jaw for accuracy did they? Only for convnienece?

[Author]

Posts