Re: Greg's Logan 820 Restoration - Initial Alignment Check
Prior to overhaul of the headstock, and total dissassembly of the bed, countershaft/motor assembly and the legs, I want to know how well it is currently aligned, and how level it is before I add the leveling legs. BTW, in my last posting, about my leveler legs, for some reason, the picture did not get correctly inserted, so here it is. [I hope my pictures attach properly this time.]
Hockey Puck Leveler Feet
On Sunday, I first checked the countershaft and its bushings. I was suspecting them to be very worn, just as the apron and gearbox shafts have been. To my surprise, I was not able to feel any play in the countershaft. I'm guessing it has already been replaced sometime over the years. Maybe a closer look when I take it apart will change my mind, but for now, it's good to go.
When I first started my machining hobby, five years ago, I became aware of the "Rollie's Dad's Method of Lathe Alignment (RDM)." But I never used it on my first lathe, an Atlas 618. It turned out to be less complex than I'd thought it was. Using a shaft cannibalized from a junk printer as my test bar, I took the horizontal and vertical measurements at 1" from the chuck, and then again at the 7" point.
RDM Vertical and Horizontal Measurement Setups
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RDM Results
Vertical, over the 6" range, I measured a 0.0027" difference at the two stations, or 0.0054 per foot, the right side is low.
Horizontally, it was 0.0018 difference, 0.0036 per foot, skewed toward the back.
Given that I never leveled the lathe, I suppose that is not too bad, is it? I wonder how much of the errors are due to bed twist rather than headstock alignment. See below....
Level Check
So how unlevel is the lathe currently, just sitting on my garage floor? Using a machinist's level, I checked across the ways next to the spindle, and at the tailstock end, about 3 feet away. Here were my setups. Note, the 2-foot carpenter's level is just used as a bridge over the saddle, not as a level.
Longitudinal and Cross-bed Level Checks
Longitudinally, the tailstock end is about 0.288 lower, over that 2 foot span. Given that garage floors are supposed to slope toward the door at somewhere around 1/8" and 1/4" per foot, that is just about right. Across the ways, measuring across the vee's (a 5" span), at the chuck end, I got about 0.026" down slope, from front to back, 0.062" per foot. At the tailstock end, 0.018" down, front to back, or 0.043" per foot.
These measurements suggest there is 0.019 twist along the 3 foot bed. Unfortunately, it is is the wrong direction to be causing the RDM horizontal skew.
Again, this was my first effort at measuring alignment and levelness, as a benchmark before I breakdown the headstock. Have I made any significant mistakes that invalidate my analysis? Or that at least need to be resolved before I actually do the alignment.
Greg