New Chuck Install

[ranchak]

I have a lathe that I just replaced the bearing, seals, rebuilt the apron, etc. I tried to align the head, but I can not get better than .005 runout. I'm using a piece of 1.5" Thompson shaft, I am not using the tail stock. I think my problem is in my chuck, I have shimmed, moved the head forward and back and all I seem to be doing is chasing the problem. I faced the old backplate and that did help abit. I ordered a backplate for a new chuck that I have, but I am afraid to machine it. I don't know if I have the head aligned or not. I don't know what step I should take next.

[LeeWay]

When I built my lathe, I used the spindle initially for alignment. One I had that aligned, I found that my chuck plate on my new chuck would not fit the new spindle. Tried it on my old lathe and it fit fine. The replacement spindle was too big to fit the relief in the plate. I then turned the diameter correctly and took a shaving off the face. Since it was very close initially, this fine tuned it and allowed the chuck plate to fit properly. I have it aligned better than .003". To get any better than this, I think I would need to grind a bit on the chuck jaw faces. This is just a tad better than the stated rating of .003" maximum run out on these chucks, so not too bad.

There was a video somewhere that shows how a fella aligned his chuck. I followed it, but don't recall where that was.

[ranchak]

I tried using the bar or shaft, taking measurements and subtracting getting the difference. But all I did was chase my tail, that's why I think my chuck is the culprit. The only thing is if I install the new backplate and take a finish cut am I going to introduce any error if my headstock is not in line with the lathe bed?

[Geof]

How are you checking the alignment?

By holding a precision bar in the chuck and running from end to end with a dial and/or checking the run out at different locations.

Or, are you gripping a piece of stock about 1-1/2" diameter and 6" long and taking a very light cut to clean it up along the full; then measuring the size near the chuck and at the end.

If you do the second operation, taking a cut along a bar thick enough that deflection is negligible any difference in diameter between near the chuck and at the end shows that the headstock, i.e. spindle, is not aligned with the bed, i.e. direction of travel of the carriage.

[ranchak]

Geof, I was doing the first method. I haven't tried taking a cut and checking the dimensions. I need to try and find a large round bar at the steel supplier tomorrow and give this a try.

[Geof]

Originally Posted by ranchak Geof, I was doing the first method. I haven't tried taking a cut and checking the dimensions. I need to try and find a large round bar at the steel supplier tomorrow and give this a try.

Yes do that.

It does not matter how the chuck is running or whether the bar runs out a considerable distance at the end; once you have machine the bar you have generated either a cylinder (cross your fingers) or a cone, that is on the centerline of the spindle.

Now you use this to true the headstock.

I have no idea how your headstock is fastened to the bed soIi will describe the approach I have taken with one held by a bolt at each corner.

You know the taper in thou's per inch from the difference in diameter over your turned bar, do remember you are measuring diameter and divide by two.

Measure the distance between the clamping bolts and you can figure out how much the head has to move at one end to correct the misalignment.

Mount a dial gauge bearing against the head stock near one of the bolts.

Slacken the bolt diagonally opposite the dial gauge and retighten it snug but not fully tight; the dial should not move.

Slacken the other three bolts and then retighten them finger tight; pinky finger pushing lightly on end of wrench tight; it is possible the dial has moved a little but don't worry.

Now take a dead blow hammer and lightly tap the headstock near the dial gauge in the direction it needs to move. This is going to shake the dial gauge so maybe you should be using a cheap one.

When the dial indicates you seem to have tapped the headstock far enough snug all the bolts down, take a light cut along your bar and re-measure it.

Go back to the slacken bolt step and repeat everything until you get the bar turned parallel to with 0.001" or better.

Now that you have a parallel bar you can check the vertical alignment of the spindle axis by mounting the dial on the carriage and running it along the top of the bar.

If you find the spindle axis is off vertically you may need to shim under the front or back bolts to get it level then redo the alignment. I would be tempted to leave it so long as it was not out more than 0.001" per inch. This typ of misalignment does not cause really serious problems.

[ranchak]

Thanks for your help guys. I got within .001 after about an hour of fiddlin' around. Now I have to mount my QCTP, and face off my new backplate. Hopefully I'll get a better finish!