Ya, thats what I was curious about. So it was a 9kg holding force, not a 9k moving force. got it.
I posted 3 days ago that the order in which you tighten the gantry bolts will effect it’s resting “squareness”.
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Also unless you are temp and humidity controlled you will be chasing this forever. I get the concern of added wear and tear on the machine…I just don’t know if the precision you are looking for is available in this machine unpowered.
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Yup, and I kept track of the order in which I snugged them, and it came out straight - at first.
And if you hit a clamp or other obstruction at one end of the gantry it will put it out again as well.
Honestly I got mine a lot closer than Avid says it needs to be and haven’t checked it since. I don’t make money with my machine so wear and tear will be low no matter what. I do take comfort in knowing there are lots of people running these day in and day out without much issue.
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So today I shimmed the gantry. 0.004" on one side and 0.007" on the other got it square enough that the motors stopped complaining. It’s still not perfect - when moving Y typically one motor draws more current than the other (which one depends on which way it’s going) so there’s still some stress in it, but it’s good enough for now.
Exactly where did you place the shims?
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Shims are about 15mm by 60mm. Each shim was put under the edge of the red plate, next to four of the eight bolts holding the red brace to the X gantry, according to which way I need to angle the gantry, so my X+ riser (shown) is shimmed on the inner edge, and my X- riser is shimmed on the outer edge.
The bolts on each side are about 40 mm apart on a 70mm plate, but the gantry ends are about 1700mm apart, so the shims are about 40/1700 to 70/1700 or 1/40th to 1/24th the amount you want to move. I ended up increasing the shim thickness after the first try, though, so I think ‘overestimate’ FTW.
To get the shim in there, you have to loosen all the bolts on that red plate, but you also have to loosen the four bolts under the grey plate between the riser and the gantry to allow the gantry to pivot. Tighten the red plate bolts first, then tighten the other four.
To measure how much you’re “off”… home your machine and leave it running, so the motors hold the gantry square. Place a dial or test indicator against the riser. I used a dial indicator set to half its range. Now loosen the spring bolt that holds the pinion against the rack until the riser is free-moving. Wiggle it back and forth by hand a little to make sure it’s at the middle of it’s “resting range”. Note measurement on the indicator.
Note that adjustments on one riser are done by shimming the other riser, but only if the side you’re adjusting has its bolts loosened, otherwise it’s affected by both risers. Obviously, if you’ve loosened the bolts, make sure your dial indicator is measuring the gantry movement and not the riser movement.
Not that I’m an expert on shimming or anything… 
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That exactly how and where I shimmed mine.
Great explanation. Thanks.
Clarification: an ideal shim would be 75-80mm, not 60mm - mine were 60mm because that’s what I had
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