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Lathe chuck master pinion

On 22 Oct 2004 19:40:24 GMT, snipped-for-privacy@w-sherwood.ih.lucent.com (Charles A. Sherwood) wrote: snip

The three screw adjustment technique for the Burnerd chuck doesn't seem to be well known so perhaps it's worth repeating

4 screw adjustment is easy - simultaneously adjust a pair of adjusters 180 deg apart to remove the eccentricity error measured in line with that pair of adjusters. Rotate 90 deg and repeat with second pair. Adjustment is easy because the adjustment planes are 90 deg apart and there is no crosstalk - each adjustment is independent and does not affect the other

With only 3 adjusters it is tempting to twiddle one and see how much it moves in that direction. This is a recipe for chasing your own tail because there is severe crosstalk between adjusters 120 deg apart. The way round this is confine adjustment to two planes 90 deg apart.

First tighten all three adjusters and rotate to check Total Indicator Reading.

Select adjuster nearest maximum run"out" First slacken the other two adjusters and then adjust the selected adjuster to halve the TIR

Take up the slack by equally tightening the remaining adjusters

Zero the indicator.

Rotate 90 deg.

Simultaneously (ie one in one out) adjust BOTH the remaining adjusters for zero reading. Because this moves the workpiece at 90 deg to the first adjustment there is no crosstalk and the first adjustment is unaffected.

With no crosstalk, a single cycle of this will get you pretty close. If a second cycle is necessary, repeat the whole cycle - don't be tempted to twiddle the odd one! It's pretty easy to get within less than a thou.

For the last few tenths the centering method used on cylindrical grinders is useful. Lightly tighten the backplate locking screws and tap into final concentricity with LIGHT taps of a lump of lead.

Jim

Reply to
pentagrid
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Here's the proper perspective and the advice here is not necessarily for you or the seasoned machinist set in his ways. It's for young dogs willing to learn new tricks. You can get precision results from a no-name cheap 3-jaw chuck. If you're going to have this on the lathe most of the time then make sure **the chuck body** is centered during installation. This is a

**one-time** activity per chuck installation and takes much less time than it would to center stock in a 4-jaw chuck which you would have to do at every stock change.

After the chuck is properly centered (runout near the accuracy of the DI/DTI) you need the indicator again to determine the master pinion and any tightening sequence if it was never done before. This is a **one-time** activity that may not have to be repeated ever again during the lifetime of the chuck (depends on the wear of the chuck). Mark the master pinion, write down or commit to memory any sequence. You use an indicator thereafter at stock changes only for confirmation and **only when you want precision results** and by that I mean near zero runout approaching the accuracy of the DTI. Basically this would be.....Tighten jaws on stock ...Check runout.....Loosen and retighten if not acceptable.....Repeat until acceptable. No where as tedious or time consuming as stock centering on a

4-jaw chuck.

Is any of the above applicable to a quality 3-jaw chuck setup? Go figure.

Reply to
oparr

Does anyone have some chuck manufacturer documentation claiming a master pinion exists?

The only thing i've seen is from Burnerd on their "Super-precision" chucks, that mention accuaracy of 30 microns by using the "nominated pinion."

Their standard accuracy chucks don't mention that feature.

I have Skinners, Buck Adjust Trus, and Cushmans upto 12", and have not seen a difference one pinion to another.

What is important are snugs threads, a tight thread register on threaded spindles, and properly fitted backplates. My Buck 3 jaw and 6 jaw 12" chucks will hold .001 on 1.25 ground bar 10 inches from the jaws, any pinion you please. If ya want better than that use a collet.

Tony

Reply to
Tony

. If ya want better than that use a collet.

Or soft jaws.

Harold

Reply to
Harold & Susan Vordos

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