Hi all, I'm trying to get my Momus CNC to cut more accurately. Currently to test accuracy I am cutting a 3" square, 0.5" Straight Cutter, 50 IPM, 75% stepover, Climb Cut. I am consistently getting a measurement of 2.98" for the x, and between 2.96 to 2.97 for the Y axis. Here is the things I have tried.
I have tried changing the speed of cut, no appreciable difference between 80 IPM, 50 IPM, and 20 IPM.
I have tried using exact stop mode, no change noted.
I tightened both the x and y belts, and the belt clamps. I also tightened the pulley set screws, but I can not tighten them too much because the set screw is tiny and is threaded in thin aluminum. No change here.
I tried loosening the bolts on the bearings. Initially the force needed to break the gantry/ carriage loose when disconnected from the belts was 6 to 10 pounds, measured with a fishing scale. Now with the bolts loosened the break loose force is reduced to under 5 lbs for both axis. Machine moves a little more smoothly but the dimensions did not improve.
I switched from 4x microstepping to 2x microstepping. No change in the x, still came out 2.98, y came out 2.95. I only did one cut like this so I'm not sure if that was a fluke or not.
So let me present what I think is wrong. Considering that changing speeds did not affect the result, I don't think the motor is loosing steps because its being over worked. The fact that loosening the bolts on the bearings and changing from 4x to 2x microstepping had no effect also leads me to believe that the motor is probably not missing steps. I'm running Kelling 425 oz in steppers, driven by Kelling KL 4030 drivers, using a UC 100 and Mach 3. Step and DIr pulse length is set to 4 micro seconds for both.
The most likely suspect is that the pulley is moving on the shaft. I am considering loctiting the pulleys on. Does anybody know how hot a stepper motor can be before the seals/insulation are damaged? I am wondering in case I have to remove the loctite.
Secondly, I heard that the spindle being poorly trammed can cause inaccuracy in the length of cut. The Momus is kind of a pain in the ass to tram the spindle, so mine is currently out of square by a bit. On the squares the ridge left behind is about as thick as a piece of paper. Somehow I doubt this is causing the cuts to come out inaccurately.
Your advice is much appreciated. Feel free to bring up anything I may have missed. I'm just looking for second thoughts before I start taking things apart.