As I've started delving more into precision work, I've run into some real strange issues with the flatness/alignment of my table.

To start with, I trammed the thing using the standard technique of sticking a dial indicator on the spindle and rotating in between extremes of the table, tapping the vertical column to get it perfectly aligned.



My dial indicator has hash marks of 0.0005", and after endless tweaking and checking, I got it so that it ready to <= 1 hash mark on each end of the rotation. As far as my beginner's eye can tell, it's perfectly trammed.

Then I mounted the dial indicator directly under the spindle so that X motion of the table was perpendicular to the direction of the indicator head to eliminate push/pull drag. What I find here is extremely puzzling.

As I travel over the RIGHT side of the table (that is, from the middle out to the right end) there is extremely little deviation in the indicator. <= 1 hash mark. However, as I travel over the LEFT side of the table (from the middle to the left end) the deviation is large and seemingly linear. Over the 5-6" of travel, the deviation is well over 0.003". You can actually see the dial smoothly moving as you turn the feedscrew.



This really puzzles me.

a.) if I can get the reading during tramming to be pretty much spot on, why would I see a difference as the table travels?

b.) why would one half of the table appear to be nearly perfectly flat, while the other half deviates so sharply?

About the best I can come up with is that the table isn't sitting in it's grooves cleanly and as it crosses the midpoint, it tilts ever so slightly. But I can't feel this, and putting weight on the left end of the table doesn't seem to change things at all.


What goes on here? Is this kind of thing normal on such a low end mill? What options do I have? It would suck to have to restrict usage of my mill to half the table