This is the "bed" without the way mounted.
I mentioned the bed and bed way are made of 1/2" by 4" cold rolled steel. As it turned out the 1/2" thickness varied by only two or three ten-thousands of and inch. Lengthwise along the flat of it was a slight bow, which as far as the way plate (top horizontal piece of bed) is concerned, will not be a problem as it will flatten when bolted to the bed.
However the side (the way surface and top bed surfaces) had a bow of about 40 to 50 thousands of and inch. This is a problem. When the way plate (top of bed) is bolted onto the two upright vertical 1/2" pieces, it would follow the bow in the bed, as well the carraige would also follow the bow of the ways.
The solution was to scrape the top surface (the two vertical pieces) and the way surfaces, especially the back way, to a dead flat state. But how in the heck do I do that? Well the solution was simple, but an awful lot of work. Scrape them flat using the old Machinist's "rule of three". Which states that if you have three surfaces that can be scraped to the point that they will fit perfectly together in any conbimation (1-2, 2-3, 1-3), then all three surfaces will be dead flat.
Thus using the top two surfaces of the two vertical pieces, and the back way surfaces for the rule of three. I ended up bed that when the way is bolted to the bed, The top two surface will be very near dead flat. Over its entire length it will be true to within less than a thousandth of an inch.
I Guess you could say I did it the hard way. I "guesstimate" it was about ten times more work than building it Gingery's way. The reason I choose to go this route is I wanted a longer heaver bed which would be much heavier and stable. And support a lathe with about a 9" center radius. Originally the bed I built was 34" long, which proved too unwieldy, I could not find a place to put it. I've since cut it down to 30", which is about perfect, giving a lathe of about 9" radius (swing?) and 16" or more between centers.
The "bed" with the carriage "way" bolted on, well screwed on with flat head screws on 4" centers. As a second thought it would have been better to use 3" center, but I was to lazy to drill all the holes, but still I wish I had. It should still be plenty strong, especially when compared to Gingery's original design.
Even though it is a very heavy, strong bed, I had to be very carefull mounting it to the bench, and shim the area around the bolt holes so it does not twist when bolted down.
When I scrapped the bed top and way sides I also made a straight edge, which is accurate to far less than a thousandth of an inch. This is the most accurate tool I own, and proved invaluable for shimming the twist out of the bed when bolted down and fitting the other ways to the carriage.