Resurfacing an MT3 taper on a SB 9

[dansawyer]

I have a 1945 SB 9a that is in good condition. I have been trying to machine some parts to tolerance and not getting the results I was hoping for. The major reason is my skill level, but in order to ensure I had a good understanding of the machine I have been taking some measurements. I have discovered some measurements that I would like to address. The first is a discrepancy between work that is held in a three jaw chuck and work that is held in an arbor in the spindle.
I am using a length of 1/2 tool steel rod in the chuck and in the arbor to measure spindle run out. Interesting the dial indicator measurement in the chuck is +/- 1.5 thousands in the chuck and +/- 5 thousands in the arbor. This is not what I expected.
I suspect the MT3 arbor is the issue. The surface is pitted and may not be seating properly. Can this arbor be resurfaced? Can it be done on this lathe?
If so what is the best way? I have seen two methods mentioned. One is to offset the tail stock and second is to use the compound feed. Which way will most likely produce the best results?

 

[Bob Korves]

Precision ground flat toolroom stones will take off the high points of nicks, burs, and dings. They will stop cutting when the main flat surface is reached. Pits and other low spots are not an accuracy issue. They work quickly and give an easily sensed (tangible) feel when the high spots are gone. My 6" electronic calipers were once the most used tool in the shop. Now it is a tie with the precision ground flat toolroom stones. They start as sharpening/honing stones, but become a completely different tool when they are precision ground flat, with a plane of flat surfaces broken up with sharp cornered crevices. They work as well on cylinders and tapered rods as they do on flat surfaces, just keep the stone square to the linear straight lines of the part or tool. They can even be used slowly under power. They will not work correctly on spheres or other similar surfaces.

 

[pacifica]

I would use a 1.5 to 2" steel rod, stick it 8 to 10" out of the chuck, take about .100 off and then see what the runout is. No tailstock used.
Assuming: your dti is accurate and ridgid.Lockdown everything you can lock down(crosslide,compound, dti holder).

 

[benmychree]

Just deburr the arbor and the taper in the spindle and see if that improves things; a morse taper reamer used carefully by hand with a cutting oil would remove small burrs in the spindle, they frequently get tiny dings that can effect accuracy, also dirt or other crud has the same effect. So far as the arbor is concerned, I'd just run a fine file over it, just to take the burrs off.