BTW, these tests are done with spindle stopped.
LOL! I think my brain was still asleep when I read your reply this morning... I couldn't, for the life of me, follow what you were telling me. I reread it later in the morning and understood it fine.
BTW, these tests are done with spindle stopped.
I never do test collars/diametrs with unsupported ends.
for true readings must be done between centers(not a chuck and a center)
center tailstock to spindle first
I was answering for the bed leveling/twist.I would think that you're penalizing yourself unnecessarily by adding yet another variable to be considered. Is the error due to headstock misalignment ? Bed wear ? Tailstock alignment ? Any combination or all ? It's admirable if one can deal with all of that but I'll stick with a simpler model - no tailstock center - to minimize the number of problems I need to think about.
After obtaining satisfactory results, the two-collar test bar can be carefully bored for centers and then used for tailstock alignment.
....Equipment at hand kinda dictates the method...
I collected enough parts to actually measure my ways with a DTI, that round bar on the inverted V is cast iron that I chucked up in the mill, its a copy of the King way alignment tool. I used a .0005 DTI, but I also have a .0001 that seemed to jump around a lot when I rolled it along the ways. I found that a light coat of oil also stopped the chatter when using the tool. Tim
http://www.hobby-machinist.com/attachments/front-way-jpg.72188/