Grinding on chuck and a live centre

[michiganbuck]

The spindle must be run/made between centers to make a live center. I believe China and the like ones are run/made out of a chucker capable of holding 2 tenths or so. With that technique, they(the junk ones) can't be point ground in place to become better than that .0002.
Making the live center spindle between centers can easily achieve 50 millionths and better.
Very likely, a good live center is made with two male centers. And finished ground between dead centers...and then the point end male center is ground in place.
At one of my jobs, I had the task of regrinding live centers. the bearings would be replaced..and then I would grind the points running in /Turning in their own bearing, the target was no detectable error. Mostly I did them on a B&S 13 grinder.

 

[NarulaMech]

I agree with much of that. But it depends on the OP and his exact reasons for wanting to get closer. I too would generally think it's folly to chase around fiddling with turning between dead centers instead of just leaving a little extra grind stock, but maybe there's something we haven't been made aware of beyond the extra grind cost. And he hasn't even mentioned heat treat. I wonder if that's even happening. Really crazy to try to leave less than .004" grind stock on parts that size if the parts are getting HT'ed after turning.

And I'll have an Omega Speedy replica, thanks.

I've forgotten to mention that part. Heat treatment.
After machining on the lathe, I send it for heat treatment. Toughening upto 30HRC, then straightened on a hydraulic press, then induction hardened to 55HRC.
Then finally goes to grinding. Which is where everything goes haywire.


What I've done is made my lathe process parallel to grinding operation using job carriers and centres. But I'm finding a face driver through which I can do OD turning in one go, whereas my current operation requires me to rotate it due to the job carrier.

Any suggestions whether a face driver is actually good. What all failures i will face using a face driver.

 

[EmGo]

What all failures i will face using a face driver.

The only tricky part is, the end of the shaft has to be big enough to get a bite. If your stuff is like 1" diameter or smaller then you have to take little teeny cuts or it's kind of iffy. But many people take little teeny cuts these days anyhow, so maybe fine for you.

 

[michiganbuck]

If the part's head center is not needed after finishing a part can be left with a bigger diameter or longer at the head end..and that feature is cut off.
Grinding should be a quick simple operation of .003 to .015 finish stock.
+- .001(.0009843) is not super close but you have to make spec easily so not to waste a lot of time measuring and/or making scrap.

I would measure the next part while one is grinding ..and so know there is .xxx stock to take, and take that stock with not measuring.
My gauge plate would be set with an indicator so a swipe of the part would tell the take amount..and tell the finished size so no handling a micrometer, or inspection would be needed.

A common live center(a junk one) may give up/error .0003 and give up much of your tolerance.
A .0002 live center belongs in the dumpster.
Advertised .000197 is the same as .0002

 

[john.k]

Simple cure.....get a centreless grinder .

 

[CarbideBob]

Simple cure.....get a centreless grinder .

Not understanding how this would work. Help me out.

 

[EmGo]

A common live center(a junk one) may give up/error .0003 and give up much of your tolerance.

C'mon, our op is nuts. Unless it's Big Four you leave .010" for grind. In the real world a few tenths is nothing.

I've done literally tens of thousands of round parts, saying "I must save grind time !" is silly. Get up ten minutes earlier and take a shit at home instead of after break, you'll save more time. The damn things just sit on a shelf for an hour waiting for UPS to arrive anyhow. Try theory of constraints.

 

[michiganbuck]

Grind stock left for finishing?..I guess that depends on the control ability of the roughing operation and possible change of the material during heat treatment..
Better roughing control allows one to estimate the wheel breakdown for each part better, so to have less time in the grind and less chance for scrap due to undersize.
At my first grinding job, we had a book that listed heat treat change of many steels. That was handy for grinding and tapping after heat-treat.
Yes, we would mark prints once the best rough size was discovered.