I've read through multiple posts on the net for how to perform the alignment of the Mill head to the column and Lathe Head to the lathe bed. I've seen shortened versions where a perfectly straight and cylindrical rod/tube is used. I've also read the versions to remove the error due to non-concentric rods.
So first off, let me say I don't want a "my method's better than your method" sort response as I've seen lately. I would like to gain some insight as to differenct scenarios that one might encounter during this process so this thread can be useful for the betterment of all. I'll post links I've found at the end.
I'll start with the first scenario (mine) to kick this off.
Mini-mill:
Head and column removed, laying face up on my workbench
My DTI measures in 0.0005"
Using the gadgetbuilder shortened method.
Measuring for Y-Axis tram, I've got the DTI located on top of the rod, near the spindle and have it zeroed at the center of the positive and negative swing (0.001" on both sides). When I move the head up the column to measure the rod for the "distant" reading I'm seeing the following. The DTI now shows a +0.0085" and a -0.01425" at a distance of 4.95" away from the near spindle measurement.
Summarized:
Near Spindle
High +0.001"
Low -0.001"
Away from Spindle (4.95")
High +0.0085"
Low -0.01425"
From what I understand, this indicates the spindle head is nodding forward, i.e., the rod tip is closer to the column than it is toward the machinist.
I'm confused from all the reading whether I'm supposed to add or subtract the numbers before dividing by two. One says one way will provide indication of "out of roundness" of the bar, another says it cancels out the radius, and another says it indicates deflection off the center of the axis. One says you don't need a test bar and another says do it this way if you have one.
Can someone tell me exactly how much I'm out of alignment and explain how you're arriving at your answer?
Thanks in advance,
Vogavt
Original Rollie's Dad's Method
Mathematical Analysis of Rollie's Dad's Method
[nomedia="http://www.youtube.com/watch?v=ZaIuHNFIFNw&feature=player_embedded"]YouTube - Rollie Dad Method - Spindle alignment on my 7x14 Lathe[/nomedia]
gadgetbuilder's Method
Jose Rodriguez's Method to Make a Test Bar