Live center accuracy, what's acceptable

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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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. :(
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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
 
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?
 
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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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
 
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.
 
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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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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