I feel a little guilty for asking a bunch of newbie questions on here, but I appreciate the help.
I performed the levelling procedure and removed twist on the bed. Using my precision bubble level, I’m dead center at the middle of X-Y travel, and front to back on the Y-axis.
I checked for table flatness, and dragging my DTI on the table from the extremes of X, I noticed a curious difference of about 5 thousandths in Z towards the very left and right edges of the table. On a hunch, I jogged left and right on X with my bubble level and found that the table is actually tilting about 6 divisions on my bubble level (0.3mm / m) at the extremes of X. That is, from dead flat in the middle of travel and then tilting around Y when jogging along X from center.
All that said, assuming the table is tilting around Y, is adjusting the gibs the recommended solution?
(I’m currently getting about 8 tenths in lost motion in X and Y FWIW, which seems reasonable)
I have squared the mill according to the instructions. Mill is perfectly level and bed twist has been removed per the Commissioning and Calibration Guide and Leveling and Squaring the Mill.
Looking around on the web, I think this might be referred to as “bed sag” or “sagging bed”.
When you say you have a 5 thou difference, is there a high point in the middle of the travel with both ends lower? Or is one end high and the other low?
If it’s the former, that sounds like the bed is sagging. The latter I would read as twist that still needs to be worked out.
Here we go. https://forums.tormach.com/t/1100mx-table-lifting/1519?u=dr_harold_jones
I went through about a year of this and there was a lot of stuff going on. I believe what was causing it was a slightly loose gib and as the table moved slower to y- the weight of the motor caused the right side of the table to lift as the weight moved farther from center. I now have a micro arc on the right side and the table stays pretty flat. You could put a medium sized child or a couple bars of gold to balance it out.
Wow! Thank you, Harold! I’ll read through your post and report back. Medium sized child, lol.
Ian, sorry if I didn’t explain very clearly. Basically the table “tilts” to the left or right depending which side of center it is jogged. When the table is far left, it tilts down on the left side. When the table is far right, it tilts down on the right side. The total difference I measured at 0.005".
I actually went through and tightened the y gib (note to folks: when tightening the gib adjustment screws, make sure you jog the table towards the screw you are adjusting, as the gib will be pushed against the adjusting screw.) last night and ended up going from 0.005" total difference from left to right to 0.003" without inducing drag. So it appears that my measured 0.003" (0.07mm) is on par with what you have found on your machine, Harold.
One last thing I did last night was measure the overall change in Z directly under the spindle from -X and +X extremes. My machine varied only 0.0002" in Z across the entire machinable area, so I think what I am observing with the Z change at the far ends of the table is probably irrelevant in practice.
It’s just weird to me that there is such a big change in Z within the last few inches at the ends of the table.
