Making a Live Center

Have a chinese live center that work ok but tried my dead center and it is more rigid when parting or during heavy cuts. If we can find a good sturdy design....

Was brainstorming some ideas:
● Using several 6000 series ball bearings? Have seen it on high speed spindles. (I'm more a taper bearing guy but it's hard to preload them in this blind hole design)
● Replacing tailstock ram completly with dedicated one? (There a internal square thread should be hard to do)
● The tree bearings design with one bearing far from others is the one I like more but into a MT02 there aren't much space.
● Think using brass bushings we can make a good sturdy (and small) live center. But it is durable?
● There something already done we can repurpose? (Like car wheel bearing pipe center)
 
mikey said:
Not being facetious; I really want to learn so that the next one I make is better.
Click to expand...

How about you show us how you measured your 3-5 micron line to line alignment? Not being facetious; I really want to learn ;-)
 
magicniner said:
How about you show us how you measured your 3-5 micron line to line alignment? Not being facetious; I really want to learn ;-)
Click to expand...

I actually hit the bore dead on, or at least as close as I could measure it with a telescoping gauge and a good micrometer. Fit was good, live center runs slightly warm in use.

I was serious. How would you make a live center? I will learn and so will the OP and others who follow.
 
mikey said:
I was serious. How would you make a live center? I will learn and so will the OP and others who follow.
Click to expand...

I visit my industrial tool supplier (TR Tooling and Machinery in Sheffield) and Make a live centre slide across the counter by sliding cash the other way, seriously, I make enough for my time that it isn't worth making tools I can buy at reasonable cost to just to be able to make things I actually want to make.

But since you ask I'd use a pre-loaded angular contact pair unit at the front with a single angular contact tail support bearing at the back, tail support bearing fixed on the shaft and able to move in it's bore with sprung pre-load on the outer from the housing.
I source my bearings from City Seals and Bearings in Sheffield and usually have a chat about the application as I did when I built my 30,000RPM ER11 mini engraving spindle for my CNC mill but in this instance, just for you, I would use the bearing Cascao used and measure the results before commenting on it's suitability for home machining ;-)

BTW, I measure my bores with one of my Diatest kits, these are two but I have the range covered from just under 1mm up to around 40mm
Diatest4.2mmto10mm.jpg

DiatestLarger.jpg

either with the OEM indicator or for less critical applications with a digital indicator capable of direct size readout to 5 tenths.
Specs here -
http://www.diatest.com/products/sol...ment-of-diameter-and-length/split-ball-probe/
Yes, I have the stand ;-)
 
ddickey said:
You'd have to be able to turn the point mounted in the MT body. There has to be a way but I wouldn't know how (keeping the center from rotating).
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Mount it in a MT socket and spin it in a spin indexer or spin fixture. on a surface grinder or tool grinder at the correct 60 degree angle. Use a shop made dog and clamp to stop the point from turning while grinding it. Disclaimer: I have never done something like that...
 
mikey said:
... how would you go about making a live center that needs to hold tight tolerances? Not being facetious; I really want to learn so that the next one I make is better.
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The only way I know to control tolerances, is to use no manufactured ball bearings (because
some suppliers don't give data, and others give... so MUCH data, in indigestible form).
So, it'd be a bronze press-in bearing fitted to a suitable taper, then single-point faced and
bored/reamed, with a slipfit solid steel center.

With the right lubricant, that could handle heavy loads (until it wears, but you can pull
and replace the bronze insert). Hmm... instead of a hobbyshop ball bearing
solution, maybe I should do the simple thing first.

Buying a two-row angular contact ball bearing gives some factory preload, and one
can hope for concentricity, but I'm not seeing a clear indication of the axial orientation
and position tolerance as a function of load. A heavy hand on the tailstock
crank can either make it more accurate, or less. As can any tailstock or steady
rest adjustment.
 
http://www.skf.com/group/products/b...nsiderations/bearing_preload/actbb/index.html
Seems like two or tree angular contact ball bearings can be a good choice. One needle bearing into taper can inprove it even more. Like ddickey pdf picture. Good design and maybe a improvement from my actual live center.

But since my lathe are small, smaller diameter would be good...

Going to bronze inserts (or needle bearings) will be awesome due small diameter.
Can needle bearings be made to spin without free play?

Was thinking about drag. A live center with much drag will not be good since it tend to act like a dead center. So, it can be a problem with bronze bearings...
 
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magicniner said:
I visit my industrial tool supplier (TR Tooling and Machinery in Sheffield) and Make a live centre slide across the counter by sliding cash the other way, seriously, I make enough for my time that it isn't worth making tools I can buy at reasonable cost to just to be able to make things I actually want to make.

But since you ask I'd use a pre-loaded angular contact pair unit at the front with a single angular contact tail support bearing at the back, tail support bearing fixed on the shaft and able to move in it's bore with sprung pre-load on the outer from the housing.
I source my bearings from City Seals and Bearings in Sheffield and usually have a chat about the application as I did when I built my 30,000RPM ER11 mini engraving spindle for my CNC mill but in this instance, just for you, I would use the bearing Cascao used and measure the results before commenting on it's suitability for home machining ;-)

BTW, I measure my bores with one of my Diatest kits, these are two but I have the range covered from just under 1mm up to around 40mm
View attachment 250503

View attachment 250504

either with the OEM indicator or for less critical applications with a digital indicator capable of direct size readout to 5 tenths.
Specs here -
http://www.diatest.com/products/sol...ment-of-diameter-and-length/split-ball-probe/
Yes, I have the stand ;-)
Click to expand...

I was honestly looking for useful information for myself and the OP. Snarkiness aside, perhaps DD can mine something from this. Thank you for your time.
 
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