gm,
Knowing whether your lathe would benefit from a bed grinding or can be put in good order solely by scraping would require a fairly thorough survey of all the way bearing surfaces to determine where any wear exists and its extent. That said, with the hardened top flat ways it would almost certainly would require grinding vs. scraping if the wear justifies it. It may be possible that hardened ways of this sort could be scraped but I have never heard of it. You could get a quick and fairly simple estimate of the top flat way condition by removing the carriage and placing an accurate straight edge (preferably a knife edge tool makers style) across their length to assess the extent of wear. I would assume it would be worn most in the area that the gib adjustment is the loosest. But, given the hardened surface, I would expect most of the wear to be on the front and rear dovetails and on the underside of the carriage. That could largely depend, though, on the type of use to which the lathe was put. For example, if used frequently to turn cast iron or in the presence of grit from tool post grinding, the carriage may act as a lap and cause significant wear to the bed ways. Rather, though, I would expect most of the wear to be to the front and rear dovetails - both on the bed and the mating surfaces on the carriage.
All the TLs that I have seen, in addition to the two that I own, have cast iron gibs on the carriage so I presume the bronze was a replacement as you intimate, also leading to the likelihood that the dovetails have been worn.
Compared to many other lathes, Hardinge tool room lathes, including certainly the TL, have one characteristic that makes them complicated to scrape into final alignment. That is that the lead screw must be in nearly the precise same location in relationship to the half-nuts as when originally fitted. Any significant deviation from that original alignment will cause the lead screw and half-nuts to not be coaxial, thus causing binding between them to a greater or lesser degree - increasing as the half-nuts approach either end of the lead screw where it is solidly supported in its mounting. While I would not rule out the possibility of moving the lead screw in its mounts or moving the half-nut in the carriage, my assessment is that both would be VERY complicated and cost/effort prohibitive.
Hence, retaining the carriage/lead screw alignment requires adding some type of material between any two bedway and carriage surfaces that have any metal removed, whether by grinding or scraping. For example, I am in the process of reconditioning an earlier model TL (cast iron flats) and had to grind about .005" off the top of the bed and will have to remove about .020" to the underside of the carriage. So my plan is to apply about .030" of Turcite to the underside of the carriage in order to be able to scrape it so that the total of .025" of material removed is "shimmed" back into original alignment. Similarly, any material removed from from the back dovetail of the bed and its corresponding surface on the carriage will have to be "shimmed" back with a suitable material (Turcite).
In addition to retaining carriage / lead screw alignment and position, there are a total of seven bed surfaces that must be restored to flatness, straightness and perpendicularity: The three surfaces comprising the split bed; the two top flat ways; and the two dovetail ways. Also, if the carriage and/or bed are worn, the tailstock shoe which contacts the split bed is almost certainly worn enough to require refitting. Scraping the shoe into complete alignment with the spindle axis is not for the timid but it is certainly attainable.
All of the above is not to discourage you from reconditioning your lathe or having it done, but rather to give an appreciation for the complexity. You seem to clearly understand that scraping is somewhat an art and is time consuming. I have no clue as to what it would cost to have done or where you would find someone who would do it more for the passion than for the compensation. As an example, about 5 years ago I had my TL bed reground by a local machinery rebuilder (just the top 5 bed surfaces) and it cost $300. I thought it a great deal. It took them 3 hours and they allowed me to watch / assist, which I believe is a rarity. However, that three hours is just a small fraction of the time it will require me to refit the remainder of the carriage and bed surfaces.
Send me a PM for contact info if you wish to see pictures or discuss details of my project.
Jim
