# Live center accuracy, what's acceptable



## Dranreb (Mar 4, 2013)

I'm looking to get a live center, seen a cheap one I might buy, is the quoted 0.0008" accuracy OK?

Can I expect some wear to occur when it's 'run in'

Do I even need to worry about any of this?

Any thoughts on this  appreciated

Bernard


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## mikey (Mar 4, 2013)

Bernard, what kind of lathe are you using? The reason I ask is that on many hobby lathes and old iron the ram in the tailstock has a significant amount of run out all by itself. Then, when you put pressure on the work piece with the ram who knows how much run out is present.

0.0008" is a not bad in a cheap live center. In a good one, like a Royal, it is unacceptable. It really depends on what you need. If you are going to hold most work in a 3-jaw chuck then I wouldn't worry about it. If you need to do precision turning on a longer piece then you are going to have issues, not just related to the live center. 

You could always make your own ...


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## Ray C (Mar 4, 2013)

Like the previous poster mentioned, the tailstock RAM may have (usually has) issues.  They often have slop if they're worn and they shift from pressure while cutting.  In general 0.00008 cannot be measured in a home shop -so I personally wouldn't worry about it.  I use live centers most of the time.  They weren't expensive (under 60 bucks) and they're well used in my shop.  -Never noticed a problem.  You'll notice that most have a screw at the back end of the morse taper.  Remove the screw and throw some gear oil in there once in a blue moon.  I think it will be just fine for virtually all normal situations.  FWIW, the only time I use a dead center is on the rare occasion I need the extra 2" of bed length or, when I need to work at the end of a shaft and the collar of the live center is taking-up too much space and interfering with the bit and tool holder positioning.

These are my general observations and others may indeed have other considerations and preferences...

Ray


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## Tony Wells (Mar 4, 2013)

The answer is...........It Depends! It depends on what you intend to do with it. Do you need to use existing center holes on workpieces that need additional operations performed on them that must run closer than that to the previously machined features? The no, it won't be acceptable. But if you don't intend to remove the piece after machining and then put it back in the machine that close, then it will be fine. There are better centers, yes, but unless you need the accuracy, spend your money on something else. 

Please take this the right way. If you're not sure that you need it, then it's likely that you don't. Most hobbyists don't work to tolerances stated on manufacturing drawings, especially just starting out in the hobby. If you had a print that you were machining to that indicated a close TIR requirement, that would dictate your needs and there would be no question. 

And on the wearing in question. Bearings generally only get looser, so I''d really expect that center to be better than the spec at first, but probably run a little warmer than normal at high speed, then as things settled in, the 0.0008 would probably represent the best average of their product representation over it's lifespan. In short, at first it would be tight and closer, then loosen up, but not all at once to 0.0008, but eventually get there. The makers would probably consider that it's life expectancy. Of course, if it serves your purposes, nothing says you can't keep using it as long as it satisfies your needs.

If it's your first live center, and the price is right, you should be fine until you can measure and object to that small amount of runout. Depending on how deep you want to get into this hobby, that might be a month, a year....or you may see that it's fine for everything you want to do.


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## Dranreb (Mar 5, 2013)

Thanks so much for all your in depth relies chaps, all very much appreciated...

Mikey, it's an Atlas...always on the ball, of course I forgot do have a little wear in the tail stock ram...:nuts:

This is one I looked at,   http://www.ebay.co.uk/itm/Medium-Du...433&pid=100040&prg=1011&rk=3&sd=160851474956&

I think it will do just fine for my usage.

Regards

Bernard


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## Tony Wells (Mar 5, 2013)

That will be fine for 90% of the work in any shop at all. At least. Most everything in a hobby shop. The other factor I forgot to mention is the weight. I see that one marked as "medium" duty. That generally limits the weight you can hang off it, but not many of us want to mess with stuff heavier that we can lift, and that doesn't exceed a medium duty limit.


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## Ray C (Mar 5, 2013)

Indeed!  And a "heavy duty" live center is quite massive and takes-up a good bit of precious working space.  Things sometimes get tight with a QCTP, holder, live center and possible follow-rest etc...

-Don't believe I've ever seen one marked as "light duty" but if I did, I'd consider getting it.

Ray




Tony Wells said:


> That will be fine for 90% of the work in any shop at all. At least. Most everything in a hobby shop. The other factor I forgot to mention is the weight. I see that one marked as "medium" duty. That generally limits the weight you can hang off it, but not many of us want to mess with stuff heavier that we can lift, and that doesn't exceed a medium duty limit.


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## Ray C (Mar 5, 2013)

Wait a minute... what am I thinking?  When I get in a space pinch, I just use a dead center.


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## Richard King (Mar 5, 2013)

I would not buy anything with more the at most .0002" run out.  Buy one that is good and it will last a lifetime.  You buy a cheap one and it affects your accuracy and will probably break in a year.  Check with Polar Tool in MPLS as they sell good quality new and used tooling for a reasonable price.


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## Splat (Mar 5, 2013)

I agree with Richard. Buy the best you can, even if you have to splurge a little and not eat for a day or two.   We can't always get what we want but I've found buying cheap usually costs me later.


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## Ray C (Mar 5, 2013)

LOL...   Rich, to a guy like you, 0.0002 must seem like a thousand miles.  :man:


Man, in my world, 0.0005 is the best I can practically/predictably strive for and in an assembly, I try to have as many 0.0005's on the "plus" side as I do on the "minus" side -and with some careful planning, the average comes-out pretty close to zero...

Still working on ways to improve the predictabilty of it though...


Ray





Richard King said:


> I would not buy anything with more the at most .0002" run out. Buy one that is good and it will last a lifetime. You buy a cheap one and it affects your accuracy and will probably break in a year. Check with Polar Tool in MPLS as they sell good quality new and used tooling for a reasonable price.


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## Dranreb (Mar 5, 2013)

Splat said:


> I agree with Richard. Buy the best you can, even if you have to splurge a little and not eat for a day or two.   We can't always get what we want but I've found buying cheap usually costs me later.



This was always my reasoning when I was working, as my business grew I got even better tools, now I'm retired I have tools I have no use for with more life left in them than there is left in me.....  :biggrin:

Bernard


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## Splat (Mar 5, 2013)

I bought two carbide-tipped dead centers from tools4cheap thinking it would ensure accuracy at reasonable cost but now I'm wondering if I should get a live center. FWIW, one of the first lathe jobs I'd like to do when I finish rebuilding my Heavy 10 is knurling 1/2" 2024 aluminum rods. Should I get a live center or would I be ok using the dead with some lubrication?


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## Ray C (Mar 5, 2013)

I think you will be fine either way.  With soft 20xx aluminum, the center hole will widen-up no matter what kind of center you use.  Check once in a while that it' s not getting too loose.  With AL, you won't need much lube.  Pack some lube in the hole and it will self-feed for a good while.

Ray




Splat said:


> I bought two carbide-tipped dead centers from tools4cheap thinking it would ensure accuracy at reasonable cost but now I'm wondering if I should get a live center. FWIW, one of the first lathe jobs I'd like to do when I finish rebuilding my Heavy 10 is knurling 1/2" 2024 aluminum rods. Should I get a live center or would I be ok using the dead with some lubrication?


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## Splat (Mar 5, 2013)

Sounds good. Thanks Ray!


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## Ulma Doctor (Mar 5, 2013)

i was taught the old way with a dead center and a tube of the yellow and black from Mc Master Carr.
i don't think i've used a live center more than a handful of times, but then again most of my tolerances just have to be to .010"
it just doesn't seem practical to buy a cheap live on sale, when an not so expensive dead will produce equal results in my opinion.
buy a good live if you're serious about your working tolerances, otherwise it might be a good lesson to learn how to use a dead center.
the old timers figured out how to do a lot things with very little at their disposal in relativity to today's ease of availability.
today's machinists have more sophisticated tools,and amazing. 
but ,i fear a lot of the old ways are being lost to time. ease takes over, not many can do things the (old) hard way if necessary.
i hope we all can keep the spirit of the old timers ,that we all share to some degree.
 to do difficult, intricate things because we can!!!!
Cheers


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## Tony Wells (Mar 5, 2013)

If you go dead center, get a carbide tipped one if you expect to get any speed out of it. Consider a half center for occasional use too, as you can face all the way to the center hole, and there is more room for tooling approach.


Anyone need a carbide tipped live center, high end, #7 MT? I have a spare.


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## Richard King (Mar 5, 2013)

When I was an apprentice many moons ago a Journeyman machinist showed me a simple way to check a dead center .  He took a ground V block and then set it on a sign plate and shim it up  until the center taper was straight or slightly lower on the small end.  Then took a ball bearing, the size depends on the size of the female center hole.  Then set a 90 deg. angle block behind the ball.  A precision ball bearing (single ball) that he put a dab of grease on it and pressed the ball into the female center at the other end of the center point.  Then laid the center in the V block with the ball resting against the angle block.  Then put a height gage with a .0001" and rested the indicator on the pointed center surface, zeroed the indicator and carefully turned the center.  Takes some practice but it works good. I never thought of it until now, I suppose you could check a live centers concentricity with the shank that way too.  If the plate was slippery, he would set everything on a piece of paper to keep it from slipping.

(I edited it after I remembered more, been over 40 yrs ago)


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## dfletch (Mar 6, 2013)

Say what?


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## Richard King (Mar 6, 2013)

I'll see if I can set it up in the shop today and show you.  I was trying to explain it, but I guess I didn't do so well.


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## jumps4 (Mar 6, 2013)

i'm not a machinist and have no training but i would think that for the tolerences that are being talked about here a live center is a needle in a hay stack and some adjustment of a tailstock is going to be required to acheive the tolerances being disgused anyway? a good machine has a heavy headstock with precision bearing then on the other end of the lathe there is the tail stock, much smaller at no where the precision of the headstock. the greater the distance from the head stock and pressure put on the cutter i cant see the precision of the live center being any more of a factor than bed rigidity and tailstock bore fit. am i missing something in my thinking. or wouldnt it be better to turn the part around in a 4jaw whenever possible  and work at the headstock end  and work towards the center for real precision at the levels you are talking about.
 I have one indicator that reads in .0001 increments but i cant figure out how to use it and not breath on it at the same time:lmao:
steve


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## Ray C (Mar 6, 2013)

Thank you!  In the home shop enviroment, they are fine.

It's a valid question for the good folks who are learning this for the first time.  Money is at a premium for all of us and we want our tool purchase to give the best bang for the buck and we want to make the right tool choices.

Yes, modern live centers (even the cheap ones these day) hold tolerances that I cannot measure and they are heavily used and holding-up fine.  And if one of them goes bad, I will thank it for it's good service then, soul-lessly throw it in the scrap pile.  -Take that back... I'll probably cut the MT3 tail off and do something else with it.


Ray





jumps4 said:


> i'm not a machinist and have no training but i would think that for the tolerences that are being talked about here a live center is a needle in a hay stack and some adjustment of a tailstock is going to be required to acheive the tolerances being disgused anyway? a good machine has a heavy headstock with precision bearing then on the other end of the lathe there is the tail stock, much smaller at no where the precision of the headstock. the greater the distance from the head stock and pressure put on the cutter i cant see the precision of the live center being any more of a factor than bed rigidity and tailstock bore fit. am i missing something in my thinking. or wouldnt it be better to turn the part around in a 4jaw whenever possible and work at the headstock end and work towards the center for real precision at the levels you are talking about.
> I have one indicator that reads in .0001 increments but i cant figure out how to use it and not breath on it at the same time:lmao:
> steve


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## Ray C (Mar 6, 2013)

Well, it just so happens, I was re-testing the lathe on the 1-week anniversary of doing a precision leveling adjustment. After that, I was checking the tailstock with an extended shaft and decided to test with a live and dead center.  Here's what the setup looked like.  You'll have to take my word for it but, the 2 collars read identically using both a live or dead center.  Measurements were taken with a micrometer reading tenths.

Not saying all live centers will perform well but, given their generally good service they give me, I never questioned that it made much difference -at least for the stuff I do.  -Darn it!  I just remembered that I have one with a long nose and I forgot to test it.  Oh well, some day...

Ray


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## Ray C (Mar 6, 2013)

Hey Rich,

I'd love to see this... to check all the centers I have (live or not).


Ray



Richard King said:


> When I was an apprentice many moons ago a Journeyman machinist showed me how to check a dead center.  He took a ground V block and a angle block,  he laid a piece of paper on a surface plate, then set the angle block on the paper and shim it up so the ball hits the center of the ball, then put the V block on the paper next to the block.  Then he had a precision ball bearing (single ball) that he put a dab of grease on it and pressed the ball into the female center at the other end of the center point.  Then laid the center in the V block with the ball resting on the angle block.  Then put a height gage with a .0001" indicator on the paper and rested the indicator on the pointed center surface, zeroed the indicator and carefully turned the center.  The paper kept everything from sliding.  Takes some practice but it works good. I never thought of it until now, I suppose you could check a live centers concentricity with the shank that way too.


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## kd4gij (Mar 7, 2013)

Ray C said:


> Thank you! In the home shop enviroment, they are fine.
> 
> It's a valid question for the good folks who are learning this for the first time. Money is at a premium for all of us and we want our tool purchase to give the best bang for the buck and we want to make the right tool choices.
> 
> ...



 If your live center gives up the goast wouldn't that make it a DEAD center.:rofl:


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## Dranreb (Mar 7, 2013)

Well, it's arrived, bigger in the hand that it looks in the photo, and seems well made. 

Being Chinese made translations can vary, the included specs say the 0.01mm accuracy, D412 here>  http://www.zhengzhoutools.com/en/cp_show.asp?id=336

I make 0.0008" = 0.02032 mm.  

Can I be bothered to quiz the seller on this?.....Ho hum..

Bernard


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## george wilson (Mar 10, 2013)

If things get really critical,the most accurate center is a dead center,preferably carbide. Just keep track how tight the rotating metal gets on it. The metal gets longer as you heat it up  working on it. A carbon center is perfectly capable of getting too hot and friction welding to the work you are doing,and shearing right off into your metal.

I managed to buy the very last can of white lead they had at the paint store way back before I had money to buy a live center. Messy stuff,though. Hard to keep it from getting on your hands.


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## Bill C. (Mar 15, 2013)

Ray C said:


> Well, it just so happens, I was re-testing the lathe on the 1-week anniversary of doing a precision leveling adjustment. After that, I was checking the tailstock with an extended shaft and decided to test with a live and dead center. Here's what the setup looked like. You'll have to take my word for it but, the 2 collars read identically using both a live or dead center. Measurements were taken with a micrometer reading tenths.
> 
> Not saying all live centers will perform well but, given their generally good service they give me, I never questioned that it made much difference -at least for the stuff I do. -Darn it! I just remembered that I have one with a long nose and I forgot to test it. Oh well, some day...
> 
> ...



Ray I like your setup.  The shops I worked in we never checked the centers. Never cut long tapers either. If I owned a lathe I would double check the centers with a test mandrel like yours.  By-the-way most of my work was chuck mounted.


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## Ray C (Mar 15, 2013)

Hi Bill...  As you probably know, with chuck-mounting, you can't test tailstock positioning worth a darn.   On the face plate is a balanced type of dog setup.  Looks a little weird but works OK.   If you look over in the Machine Rebuilding section, as well as a thread called YALB Yet Another Lathe Bench.  You'll see a ton of information about how to check lathe alignment.  I learned a lot in the process of this.  My last lathe was very old and worn out and it couln't really cut straight enough to make a difference. My very first lathe was a monster and was properly setup when I started using it.  This is the 1st time I'm going though my own setup really although I did learn a lot over a few years trying to make an antiquated and worn lathe run well.


Ray




Bill C. said:


> Ray I like your setup. The shops I worked in we never checked the centers. Never cut long tapers either. If I owned a lathe I would double check the centers with a test mandrel like yours. By-the-way most of my work was chuck mounted.


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## refinery Mike (Mar 15, 2013)

I like the live center because i do not have to worry about getting some swarf in the greese. then when you put it back in the lathe it chews up your work and your center. (Been there done that) But runout is not the only thing to think about when buying a live center. The cheep Chinese live centers may only last a year and then get so loose the bit chatters like crazy. (Been there done that). Might be better to go for a middle of the road live center, for a hobby lathe. Does anyone else remember when a live center was a plain center that was actually hardened, and a dead center was left soft. (for the head stock)


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## Tony Wells (Mar 15, 2013)

I remember when a "live" center was the one in the headstock spindle, and supported work turned between centers, and the "dead" one didn't rotate and was found in the tailstock.


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## refinery Mike (Mar 16, 2013)

Yea you are right tony, it has been a long time! And my memory is not the greatest!


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## Ray C (Mar 16, 2013)

Hi Mike / All...

I don't know if all centers work this way but my cheapo brand (3 of them, one really small, one medium and one medium w/long nose) have a screw at the end of the taper to oil the bearings.  I throw a squirt of oil in there once in a while and all are working fine as far as I can tell.

Ray




refinery Mike said:


> I like the live center because i do not have to worry about getting some swarf in the greese. then when you put it back in the lathe it chews up your work and your center. (Been there done that) But runout is not the only thing to think about when buying a live center. The cheep Chinese live centers may only last a year and then get so loose the bit chatters like crazy. (Been there done that). Might be better to go for a middle of the road live center, for a hobby lathe. Does anyone else remember when a live center was a plain center that was actually hardened, and a dead center was left soft. (for the head stock)


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## The Liberal Arts Garage (Aug 23, 2014)

Ulma Doctor said:


> i was taught the old way with a dead center and a tube of the yellow and black from Mc Master Carr.
> i don't think i've used a live center more than a handful of times, but then again most of my tolerances just have to be to .010"
> it just doesn't seem practical to buy a cheap live on sale, when an not so expensive dead will produce equal results in my opinion.
> buy a good live if you're serious about your working tolerances, otherwise it might be a good lesson to learn how to use a dead center.
> ...


            This may be a good time to mention a physics / math / chem. teacher who could be quite
angry with students who implied accuracy beyond the supplied numbers or measurements. Sometimes a bit o/s and some diamond paper is th best fit. I used to mix anti- sieze with a few 
drops of heavy oil for dead centers......BLJHB


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## xalky (Aug 23, 2014)

I have some older live centers that, if pushed a little hard, will flex, .001 to.002. I don't throw them out, I use them when I'm hogging, taking heavy cuts. Why stress the good ones! When I get towards the final 2 lighter cuts I'll change  the worn one with the new one. I do use a dead center in the tail stock occasionally, but it's a fine line between not tight enough, and to much heat. I only use a dead center in the tail, when I can't get close enough with the cutter because of live center diameter being too large.


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