Alignment Problems with Large Table Assembly

Saturday, February 4, 2012
While tramming the head on my mini mill (after installing the larger table), I came across an unexpected snag. I attached the dial test indicator to the spindle with a quill-style holder and prepared to zero it out on the right side of the table, but I noticed that swinging it across the table changed the reading. In fact, after zeroing the indicator on the front of the table, the probe didn't touch the surface on the back. Checking the column with a square showed a 1/8" runout over 6". Apparently something went terribly wrong, so I started troubleshooting. I took the column off the table, cleaned the surface, ran a file across the edge to make sure there were no burrs.
Problem Fixed
When I started reinstalling the column, the screws wouldn't go in. In fact, the hole were way off. Looking closer at the base casting, I discovered the culprit: it looks like the mold halves didn't alight properly during the casting, so there was a 1/4" lip. Apparently the bottom of the column pressed against it, and tightening the screw tilted the column forward. The picture on the left shows the original condition.
Upon closer inspection it looked like the column was catching the lip by no more than 1/8" or. After "going medeval" with a Dremel it looked like the problem was solved, but the bolts still didn't align very well. Some basic measurements showed that the center hole on my bracket was closer to the line going between the two other holes (i.e. they were closer along the Y axis than the holes on the table). All I had to do was to enlarge the center hole and the mill came together like a charm.
Almost Perfect
Rechecking the alignment showed less than 0.0005" of difference between the front and the back of the table, which I'm going to call "good enough for me". I hope mine was a freak accident, and other tables don't have this problem, but as you can see, the fix is pretty easy. Including the troubleshooting, I think the whole thing took no more than an hour. Plus, I had a reason to take out the Dremmel that hasn't been out of it's box for years.

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