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4GSR
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.................. If your tailstock end is not bolted down, get it bolt down and leveled good. Secondly of all the surfaces on your lathe to check the B and F in the above drawings are the only 2 surfaces that meant absolutely nothing. On war production machines this surface was not stoned polished or even scraped, they were simply planed. None of the carriage rides on this in any way shape or form so they are not a means of measuring the ways at all for wear.
To check for wear see if there is a ridge on the A,C, E or G surfaces, these would indicate wear and these are the only surfaces the carriage should ride on. If the carriage rides on B and F, the carriage itself is worn badly and not necessarily the ways.
Hate to bust your bubble, My dad's SBL has never had the tailstock end of the bed bolted down tight, ever! Always left loose. With this in mind, the bed ways are still in the same plane, dead straight and accurate, as it left the factory in 1949. It's never been leveled that I can recall all the years I've used it. I just recently checked the alignment with a "verfied" test bar. For a almost 70 year old lathe, it checked within 0.0010" in 6" in two planes 90 degrees from each other. Not bad for a lathe that South Bend called a "work shop" lathe.
And without the bed being put on a planer or way grinder to check wear, you always look for machined surfaces that are not worn. They don't have to be scraped, since the scraped portion of the ways started out planed surfaces, along with all the other parts of the bed, ALL in the same setup. Having said that, surfaces B and F as Dabber mentioned above can be used as reference surfaces for determining wear on bed ways. You don't use surfaces D, E, G, or H as Dabber has referenced. Those surfaces WILL have some sort of wear to them. And you don't use the tailstock ways neither. I've seen tailstock ways with just about as much wear as the carriage ways have.
Oh, I forgot to mention one other thing, South Bend Lathe only planed the beds smooth on the unhardened beds. They did not scrape them flat. They did lay very light flaking or frosting to the ways. This was the most common way lathe manufactures did the beds before the days of harden & ground bed ways. There were a few like Harlindge that did scrape their beds for super accuracy.
Ken
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