Well, I measured the dovetails on the cross-slide, and they seem pretty good, no more than a thousandth of wear on the male slide on the carriage. The gib is visibly worn.
While I had the cross-slide off, I noticed two nubs that seem to ride on the top of the male dovetail, leaving a mark. I was trying to install the Cross Slide Shield (which goes between cross slide and the carriage, slides back and forth, and keeps swarf off the cross slide screw), and these nubs were interfering.
They were also preventing the cross-slide dovetail from fully seating, which made the joint springy.
The nubs are the filed-off ends of the two hex socket flat head 1/4-20 screws that hold the Screw Cover to the cross-slide. They do not appear original, were cut to length with a hacksaw, and are simply too long. They are also in bad shape. Replaced both screws, filing the length so that it does not protrude.
Put gib back in up side down (the gib is symmetric), so the worn surface is no longer against the moving dovetail.
It does seem to help, though I have not tried to cut anything off.
I also had to tighten the compound gib.
The following was done before doing the above work on the lathe.
What I did try was to trepan through a 3.4" thick 6" by 6" piece of 6061 aluminum plate held in the four jaw chuck. The intended diameter of the hole was 2.25". I was using a 3/16" HSS tool bit ground to suit the purpose held in a BXA-6 toolholder.
There was some drama. At high speed (not back gear), it chattered. With backgear, it didn't chatter but it did vibrate and generate flake chips. The toolholder and toolpost were tilting visibly. What was happening is that when the toolpost et al tilted, it dug the toolbit deeper into the workpiece, in a vicious circle, so one could not gently peel a nice chip off. You could see the toolbit itself bending. I didn't know that HSS could be bent. Anyway, it eventually broke. Part of the problem was the large overhang needed to avoid the jaws of the
4-jaw chuck; this overhand has considerable leverage, and together with the height of the toolbit over the slide increases the depth of the self-feed into the workpiece.After working on the cross-slide, I tried face grooving again, and was far more successful, although it still chattered, and I did manage to break another 3/16" HSS tool bit.
I'm wondering if the whole carriage is tilting a bit, but the dovetails are the first place to improve. I can test the carriage theory by supporting the overhanging tool with a bar resting on the arms of the carriage, or using a different holder.
Anyway, I did manage to cut the initial hole in the aluminum plate using a hole saw, and had no problem boring the hole out to 2.670" diameter. No chatter, no gouging. Nor did I have any problem facing the plate.
Joe Gwinn