RJ,
What you are saying is half way correct.
Once you get the headstock aligned correctly with the bed and cutting correctly, OD, ID turning that is, then as you said start working on fixing the concave condition. This is where it becomes a pain in the a$$ to do, and it is not not easy to do and fix. I can't say that I can do it without difficulties, and I have most of the tools needed to fix it!
And the way to fix this is by going in and re-scraping the saddle to correct the 90 degree alignment. You have to decide by careful measurements if you re-scrape the bearings or shears that contact the bed ways or the dovetails on the cross slide ways to correct and remedy the problem. If your saddle is heavily worn, may be better off going in and re-machining the way surfaces or shears, as the guys across the pond call them, to correct the alignment issues. But doing that opens up pandora's box, creating new problems that have to be addressed, too. Ken
A bit of context here. The lathe is two years old and has less than fifty hours on it. The 602 has a two bolt mounting system and when I set it up, I mounted it to a piece of 7" channel welded into a custom bench and clamped it tightly. I noticed that I had a significant taper and perhaps erroneously adjusted the headstock to correct it.
What I may have done was cant the headstock to correct a twist in the ways but two wrongs don't make a right.
The original taper decreased moving away from the headstock. Twisting the head counterclockwise corrected the taper issue but, if it were originally correctly oriented relative to the ways and crossfeed, it would now cut a convex face.
I would have to assume that when the lathe was aligned in the factory, that the headstock was more or less correctly aligned to the ways . By wrongly readjusting it to correct a twist that I most likely made in the ways, I messed up the relationship to the cross feed ways. I verified that taper was .0008/12" with the tight tailstock mounting and loosened the mount and remeasured. I was now -.002"/12" and I would have to rotate the headstock clockwise to correct which supports the assumption that I had adjusted the headstock in error in the first place.
I haven't done the readjustment yet because of the difficulty at getting at the headstock bolts and I want to properly check the lathe level and so need to acquire a machinist's level.
So my plan of attack is to 1. loosen the mounting bolts to remove as much external bias as possible; 2. check the overall level of the unbiased machine, correcting any serious issues; 3. adjust the headstock alignment to perpendicular to the cross feed ways (this can be checked by marking a spot on the face plate, mounting and indicator on the cross feed table, and measuring the runout from a position near the front to one near the back); 4. check for taper, using RDM method, shimming the far end base to correct, if necessary. I would then go back and recheck the cross feed for proper alignment and repeat, if necessary.
If this doesn't correct the misalignment of the cross feed to the spindle, then reworking of the cross feed ways would be a solution but I prefer not to take that route without exploring other options first as it is laborious and irreversible.
