Accurate Live Centre?

I have a Myford lathe with a MT2 tailstock.

I am looking to buy a very accurate live centre with a long reach so that I can get my tools to the work easily.

I have a Gepy live centre at the moment (made in Switzerland) which is VERY nice to use but I need more access.

I see that there is a Royal brand which gurantees 0.0001" TIR but are there any other very wellmade brands that I could consider. Thank you in anticipation. Chris Harris

Truely accurate live centers can be very expensive. They are after all little short machine tool spindles whose bearings determine the rotating axis that ultimately affects the roundness limits they will hold.

We had an old Landis roll grinder that had #21 B&S live centers that were nothing much more than old relics. We has no end of trouble holding 0.0002" tolerance and the work pieces were so heavy (big M/G armatures, weighed tons) that HSS and even carbide dead centers would not hold up. We paid a fortune for a live center warranted to 50 millionths and it worked until someone dropped it on its tip. Back to the factory for a $9000 re-build (1981).

One thing many fail to realize is that live centers (especially the long ones) have several times the deflection under load than a dead center having the same overhang. The errors introduced by deflection is exacerbated by the inevitably potato shaped orbit described by a live center's bearing axis. For that reason I strongly reccommend that people wishing to hold close tolerances do so using a dead center.

A Myford lathe for all its superb design and amazing versatility is quite flexible when the demands of holding very close tolerances are considered. My own lathe is quite accurate and being larger much more rigid but it still has its limitations when it comes to holding close tolerances. 35 years has taken its toll. My last roundess specimens came back ahowing 70 millionths roundness error; unacceptable for grade 5 bearing fits.

I have a selection of Sunnen external honing stones I stole from work over the years. These, when scientifically applied to work having a few thousandths finishing stock, will result in bearing fit sizes and roundnesses to the sub "tenth" range if need be. Work made this fussy is wasteful of time but its sometimes warrented when finishing spindles and other very close tolerance parts.

Good luck in finding a live center that suit your needs. I suggest that out take a good look at "cut away" or "half" dead centers whichhave the 60 degree cone clearanced on one side for wheel run-off on a surface grinder and for very small diameter work on engine lathes.

Thank you Forest. $9000 to repair a centre! Must have been pricy to buy.

I did forget to mention the type of work I am doing. The heaviest stuff at the moment are rifle barrels.

I will look into the cut-out centres. That does make sense.

Do you know what is a reasonable price to pay for a LC with less than 0.0001" TIR? I was hoping that $400 would cover it. What brands are worthwhile looking at?

thanks again

Chris

Have had good luck with these on small manual lathes.

http://www.riten.com/products/live_centers/spring_loaded_concentric_live_centers/

Not sure on the runout specs. Riten makes good stuff. Asking for less than a "tenth" runout for under $400 might be asking a lot. You could e-mail them about your requirements.

Royal comes to mind.

Rifle barrels? 0.0001" tolerances? I know target shooters like to gold plate their stuff to tighten up their group but this seems overkill.

Chris,
"G" series
http://www.readytool.com/Replaceable%20Points%20G-Series.htm

Les H.

Dead centers are probbibly more accurate But the center is just one part of the problem There is also the centerhole These live centers have only use in a very accurate, ground, centerhole And a 0.0001" accurate live center on a Myford is worth it but then it has to be a cilindrical grinder not a lathe

I looked at all three (Riten, Royal and G Series and they all look good.

I do need the low TIR as I am doing specialised bench rest rifle barrels and they need everything they can get. Most of the top BR gunsmiths today are working to 0.0005" or less. I agree that there is more error in the barrel blank to start with but the idea is to minimise the compounding of runout and eccentricity.

I am curios to know why the one post seemed to indicate that a Myford is not capable of such low tolerance. I have a new Connoisseur and it turns extremely well. I do not think they are very popular in the US for some reason - I guess the exchange rate makes it very tough for them to compete against the local lathes.

Thanks again for the feedback and help. I will call these suppliers tomorrow.

Chris

Forest ,I'm fascinated to hear about your "gold plated" running centres, as we all know a centre is only as good as the centre hole in the component , did you have any special procedures for centring the work ? The place I worked at used " Lunzer" running centres for turning and solid dead centres for grinding large chilled iron rolls, because some of the rolls were out of balance we had endless problems with the grinding process. We used to lose several centres a year to the crane drivers with itchy trigger fingers , good job they weren't that expensive. Regards Tyrone.

I like the Nakane brand centers. Made in Japan. Advertised runout is very small. Price is moderate. I like it because the head is small, so I can get in close on small stuff. I have a nice Royal that I hardly use because it gets in the way.

To be honest i do,nt use live centers,the cheepos are not worth having,the expensive ones slightly better,the only really positive centre is a dead centre,
Chris,i think the reason why Myfords are not popular in the US,its the price,and what you get for your money,its a hobby lathe,thousands of model engineers have bought Myfords lathes,they did,nt have much choice at the time,but now we have chinese lathes,are they as good,i do,nt know,but they are 1/3 of the price of a Myford,

Chris

I'm inclined to agree with Forrest, .0001 live center for a rifle barrel, are you needing this accuracy for threading of the shank? Think its a bit of overkill.

Mike

I have one of the Riten "small" live centers Jeff mentioned above and like it alot. I have done no runout studies but it produces nice work on a 10EE.

Ritten guarantees this live center to .0001
http://tinyurl.com/mcctb
List price is $312.

Royal guarantees .0001 or better at $281 list:
http://www.royalprod.com/content/files/products/2006_Royal_Catalog_Pg_11.pdf

As many have said, tenths in any lathe is tough. A larger machine, something with a #3MT or #4MT in the tailstock, would probably be easier to use to achieve this accuracy level.

How do I know this? From sometimes having to work to that level with a 10K South Bend (#2MT tailstock )

It's true that centered work has to fit the centers. Fortunately dead centered work has high initial wear so it soon fits perfectly.

For work small enough to to single hand I used an Excello center lap to fine-tune/move a center hole. I don't have a center lap at home but I have put work in place on dead centers in the lathe, run a long drift down the spindle, and bumped the drift with a heavy hammer. The object here is to have the work centered in line and drive the headstock center into it and the tailstock center with a shock. Works quite well and catches both ends within the limits of mass and elasticity. Here again is where a nudge from the machinist's large slow hammer is superior to a sharp impact. The headstock center is unseated for an instant then promptly re-seats.

In larger work with significant weight it's better to scrape for contact. Very heavy long work poses no problem because it soon deforms to a good fit with the live center.

Regardless, I don't trust a center drilled hole for highly accurate work without taking a tiny cut on it using a pointy tool and the compound set at the cone half angle.

Also there is a combination center drill touted for use in highly accurate work that cuts a radius in the flank of the cone. This makes initital line contact with the center and a moment's wear brings it into true.

The old NBS had some material they investigated and written on the subject of centering work for high accuracy. Anyone wanna fish for it?

Chris,
I am re-raising this as I have just found it. Was on holiday abroad at the time.

I do not want to denigrate or even argue about what has been said but***************!

The problem which you are experiencing does not lie with the tailstock and its attendant centre.
It lies with the inability of the tool holder configuration to get close to work in hand.
The prooblem was written about and published by J A Radford in his Improvements for the Lathe. The Publisher was Tee and the re-designed top slide drawings published.
Hemingwaykits has now done a new( well, re-issued) toolholder kit. At this point,, I do not know whether it is the Thomas or the original Radford one.

Again, Martin Cleeve in the 50's modified his whole saddle assembly. Presently, I am doing a thing on him. I suspect that he overcome the problem by a new tool holder which is also in Hemingwaykits.

I think that you really should get the two Thomas books and the Radford one as the designs are tailored for the Myford

Cheers

Norm

I like the Nakane brand centers. Made in Japan. Advertised runout is very small. Price is moderate. I like it because the head is small, so I can get in close on small stuff.

Click to expand...

Hear, hear. They have the smallest OD with the biggest point and least overhang I ever saw. Can't find anybody to rebuild them in the US, but what the heck, they're reasonably priced and available from MSC.

7 x 31, 220lb lathe with a 1" spindle bore? Or is there another model of Connoisseur?

Don't fool yourself. Buy a Royal with an extended point and don't give it another moments thought.

"I am curios to know why the one post seemed to indicate that a Myford is not capable of such low tolerance. I have a new Connoisseur and it turns extremely well. I do not think they are very popular in the US for some reason - I guess the exchange rate makes it very tough for them to compete against the local lathes."

The exchange rate has far less to do with it than the retail new price that they sell for now. They are in a price range where they compete directly with real toolroom lathes, rather than the gentlemans toy that they are.

A good friend of mine bought a new in the box, delivered from the factory, Myford about 15 years back and it was reasonably priced at about $2000 or so with a PILE of tooling. Same basic machine is now over $12K, closer to 17K if you want to load it with tooling.

I like my old Super 7, but if I had that kind of money to spend, there are a pile of FAR more capable and accurate lathes out there to buy than the cheesy little Myford!

Hardinge, Feeler, Weiler, Schaublin, Graziano are a couple names off the top of my head. Even in a used lathe, better than a new Myford could be expected. About the only place that the Myford really has anything over the names above is portability, hardly the harbringer of accuracy.

Get a carbide tipped dead center. Zero point zero runout. Always. Then it's all up to the setup.

I like my Myford! I'd be dam*ed if I'd buy one new when I could have a real lathe for the price though!

Cheers
Trevor Jones

I was hoping that someone with a Myford would come out from somewhere and verify my recommendations for Chris.

Ah, well? Cast your bread on the waters-----
and it comes back----------------------soggy!

Norm