need some tramming help

[ARC-170]

I'm trying to tram up my LMS 3990. Here are the indicator readings before and after:

I'm clearly doing something wrong because it's nowhere close! My thought was to bring the 3 lower points (A, B, D) to the same level as the highest point (C). I thought it made sense to do all 4 at once. I thought I was making all 4 points the same height.

I'm using the shims from LMS and torquing everything down the same with a torque wrench. The head up and down movement is locked. I check zero after making the measurements.

 

[mikey]

Instead of reading the corners, I prefer to take readings in line with the X and Y axes because these are the directions the table moves. I focus on getting the X-axis readings close to level, then do the same for Y. Anytime you change one point it will affect ALL of them so you have to be patient. It is wise to use horseshoe-shaped shims that surround the bolt to reduce the risk of cracking the casting, and I also agree with you that you should torque each column bolt.

 

[ARC-170]

I got it! I was putting the shims on the wrong sides. I needed to do the opposite. For example, if I got a reading of +.005, that means to add shims at that corner, not the opposite one. If I got -.001, that means to subtract that much.

Actually, I added half the difference per some research I did; so if I got +.005 and -.001, I added .003 (half of the .006 difference). It got it close, because as mikey pointed out, adding shims to one affects all the other ones. My table is within .002 over about 10" which is what the manual recommends and is about .0002/inch (factory spec is .0005/in).