I just glued on my 3 jaw chuck...

[mikey]

Guess we will see. Huh?


I'd be pretty excited with 0.001" repeatability.

I'm not trying to discourage you, Batmanacw; just wanted to comment, okay?

The accuracy of all lathe work holding devices is not achieved by the spindle mount, but by the mechanism used by the chuck to hold the work. Then there is the phase of the work, either a first or second operation.

A 3 jaw chuck is a first operation device and it will turn a nominal work piece dead on the lathe's centerline in a first op, the first time you turn it. However, for a second op where the previously turned work piece is removed from the chuck and then placed back in the 3 jaw chuck, no matter how accurate the spindle mount is the chuck will run out varying amounts depending on where on the scroll you are. This is just the nature of a scroll chuck, regardless of the number of jaws the chuck has. What's more, the more wear the chuck has, the greater the run out will be in a second op. The converse is also true; the less worn the chuck is, the less run out it will have in a second op but it will still run out too much for precision work.

A 4 jaw independent can be dialed in precisely. This chuck can be used for both first and second operations and is the most versatile of all chucks. It is also the slowest to employ and it can mark or mar a finely finished, knurled or threaded surface so it is not a panacea.

Collet chucks rely on the accuracy of the tapers in the chuck so concentricity of taper to the spindle matters here. Much attention is paid to how well the chuck fits the spindle mount.

There is nothing wrong with trying for the best spindle mount for your chuck. Just understand the nature of the device you're working with.

 

[mikey]

I chucked up the gauge pin 10 times being careful not to disturb my jb weld.

I averaged around 0.0003" run out. Better with less clamping force. I got 0.0004" as the worst. 0.0001" as the best.

The other poster was correct. It didn't repeat flawlessly but holy smokes is that accurate for a 3 jaw.

The way to test your thesis is to turn some nominal stock in a first op; it should have zero run out. Then remove the work piece and rechuck it and then see what you get.

 

[Batmanacw]

I'm not trying to discourage you, Batmanacw; just wanted to comment, okay?

The accuracy of all lathe work holding devices is not achieved by the spindle mount, but by the mechanism used by the chuck to hold the work. Then there is the phase of the work, either a first or second operation.

A 3 jaw chuck is a first operation device and it will turn a nominal work piece dead on the lathe's centerline in a first op, the first time you turn it. However, for a second op where the previously turned work piece is removed from the chuck and then placed back in the 3 jaw chuck, no matter how accurate the spindle mount is the chuck will run out varying amounts depending on where on the scroll you are. This is just the nature of a scroll chuck, regardless of the number of jaws the chuck has. What's more, the more wear the chuck has, the greater the run out will be in a second op. The converse is also true; the less worn the chuck is, the less run out it will have in a second op but it will still run out too much for precision work.

A 4 jaw independent can be dialed in precisely. This chuck can be used for both first and second operations and is the most versatile of all chucks. It is also the slowest to employ and it can mark or mar a finely finished, knurled or threaded surface so it is not a panacea.

Collet chucks rely on the accuracy of the tapers in the chuck so concentricity of taper to the spindle matters here. Much attention is paid to how well the chuck fits the spindle mount.

There is nothing wrong with trying for the best spindle mount for your chuck. Just understand the nature of the device you're working with.

I'm simply removing about 0.003" of slop in the fit. If I can throw my 3 jaw in and get 0.001" of run out consistently I'd be happy with it for 90% of the stuff I do. I've dealt with 0.005" in my old lathe for years.

I don't do tons high precision work but I have no issues making straight parts. Lots of tricks for that.

 

[rwm]

I have to say, my Bison 3 jaw is accurate to about .001-.002" everywhere I have checked on the scroll (various diameters). When I dial in something on the 4 jaw I have trouble getting to .001". I get the theory, but in practice I rarely change over to the 4 jaw with this chuck in the mix.
Robert

 

[mikey]

I'm simply removing about 0.003" of slop in the fit. If I can throw my 3 jaw in and get 0.001" of run out consistently I'd be happy with it for 90% of the stuff I do. I've dealt with 0.005" in my old lathe for years.

I don't do tons high precision work but I have no issues making straight parts. Lots of tricks for that.

I totally get it. We all try for the best fit of a chuck on the spindle. I just wanted to point out that with a scroll chuck, what goes on in front of the chuck does not rely much on what goes on in back of the chuck.

 

[Batmanacw]

I have to say, my Bison 3 jaw is accurate to about .001-.002" everywhere I have checked on the scroll (various diameters). When I dial in something on the 4 jaw I have trouble getting to .001". I get the theory, but in practice I rarely change over to the 4 jaw with this chuck in the mix.
Robert

The hardest part of dialing in on a 4 jaw is not getting too tight before you have it really close. It just takes practice. I haven't even used the 4 jaw on my 1030 yet. I don't mind 4 jaws but I just haven't needed it.

 

[MrWhoopee]

I've mentioned this before, but it bears repeating. You can dial in a workpiece in a 3-jaw using a soft hammer. Snug the part (not tight) in the chuck and indicate. Tap the high jaw with your soft hammer and snug the chuck a little tighter. Indicate again, tap the high jaw again and tighten some more. Three times is usually enough to get within .001. Working machinists are generally efficient (lazy), and this is much easier and faster than mounting a 12 in. 4-jaw.

 

[Batmanacw]

I've mentioned this before, but it bears repeating. You can dial in a workpiece in a 3-jaw using a soft hammer. Snug (not tight) the part in the chuck and indicate. Tap the high jaw with your soft hammer and snug the chuck a little tighter. Indicate again, tap the high jaw again and tighten some more. Three times is usually enough to get within .001. Working machinists are generally efficient (lazy), and this is much easier and faster than mounting a 12 in. 4-jaw.

I am fortunate that this 3 jaw holds darn straight as well as low run out. I got to my collet chuck when I can because it assists me in my laziness. Even with dialing it it only takes a couple minutes and it holds nearly dead straight. The 4 jaw will come out the moment I get an odd shaped or bigger part.

 

[pacifica]

I chucked up the gauge pin 10 times being careful not to disturb my jb weld.

I averaged around 0.0003" run out. Better with less clamping force. I got 0.0004" as the worst. 0.0001" as the best.

The other poster was correct. It didn't repeat flawlessly but holy smokes is that accurate for a 3 jaw.

See what you get with different size pins.

 

[ErichKeane]

See what you get with different size pins.

Yep, this is going to be the key. Even a $1000 3-jaw chuck isn't consistent more than ~2-3 thou throughout its holding range.