I have an old Smithy AT-300 lathe/Mill combo that I've been using for years. I've chambered some bolt actions that hold 1/2 moa groups with ease and can cut very accurately with it, but I have a minor (to me) problem that I'm not real certain about.
My 3 jaw has about .001 runout, so I do most of my precision work with a 4 jaw but I have an issue with it. Actually, the same issue pops up when I put the indicator on something in the 3 jaw as well.
When I set up something, say for example a piece of drill rod in either the 3 or 4 jaw, then put the indicator on it in a magnetic base, then rotate the chuck by hand, there is about 4-5 degrees of rotation in the chuck before I feel the belts and pulleys in the gearbox start to turn. This slack, per-se doesn't bother me, but right at the moment the slack is taken up, the indicator needle moves up by .0005.
The needle stays there, .0005 over where it was before I started rotating the chuck by hand. As long as im applying pressure keeping the slack out of the pulleys it stays there. If I take my hand off the chuck, the needle drops .0005.
So basically, I start turning the chuck by hand and when the slack is taken up and the electric motor starts to turn with the chuck, the indicator needle goes up by .0005. when I stop turning the chuck, the needle drops back to its original position, it drops by .0005 back to its original position.
The headstock feels rock solid, I cant feel any "give" in the headstock bearings, but I cant dial in any better than .0005 with this "slack".
What ive been doing to dial it in is to rotate the chuck until the slack is out and I can feel the resistance of the electric motor, then zero the indicator while maintaining this pressure on the chuck. The I rotate it, measure the runout, adjust the chuck by half the indicated runout, and measure again, over and over until dialed in. All while, very annoyingly, maintaining a torsional pressure on the chuck to keep the .0005 of slop from jacking up my progress.
What might it be?
I'm not as articulate as id like to be, does my explanation make sense?
My 3 jaw has about .001 runout, so I do most of my precision work with a 4 jaw but I have an issue with it. Actually, the same issue pops up when I put the indicator on something in the 3 jaw as well.
When I set up something, say for example a piece of drill rod in either the 3 or 4 jaw, then put the indicator on it in a magnetic base, then rotate the chuck by hand, there is about 4-5 degrees of rotation in the chuck before I feel the belts and pulleys in the gearbox start to turn. This slack, per-se doesn't bother me, but right at the moment the slack is taken up, the indicator needle moves up by .0005.
The needle stays there, .0005 over where it was before I started rotating the chuck by hand. As long as im applying pressure keeping the slack out of the pulleys it stays there. If I take my hand off the chuck, the needle drops .0005.
So basically, I start turning the chuck by hand and when the slack is taken up and the electric motor starts to turn with the chuck, the indicator needle goes up by .0005. when I stop turning the chuck, the needle drops back to its original position, it drops by .0005 back to its original position.
The headstock feels rock solid, I cant feel any "give" in the headstock bearings, but I cant dial in any better than .0005 with this "slack".
What ive been doing to dial it in is to rotate the chuck until the slack is out and I can feel the resistance of the electric motor, then zero the indicator while maintaining this pressure on the chuck. The I rotate it, measure the runout, adjust the chuck by half the indicated runout, and measure again, over and over until dialed in. All while, very annoyingly, maintaining a torsional pressure on the chuck to keep the .0005 of slop from jacking up my progress.
What might it be?
I'm not as articulate as id like to be, does my explanation make sense?
