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prinknash

Vertical walls are very slanted

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Most likely you have loose pulleys on the X-axis mechanism. Be sure and tighten the motor and belt pulleys.

While you are doing that, check that the head moves relatively easily by hand when the machine is powered off, in both X and Y directions. If it feels tighter in one direction, or stickier in some parts of the bed, then make sure that everything is square, and lubricate the rods with a little light oil (e.g., sewing machine oil). You might also try loosening the end caps on the rods a little, and see if that makes the head easier to move - sometime the end caps can bind on the ends of the rods.

 

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Thanks for the ideas. I've checked them out.

The pulleys are very tight. I can't find slip anywhere in them. The head moves easily, and with the same amount of force in both the x and y directions and over the whole bed. The amount of slant is constant and seems to keep going (tallest part I've made is 2 inches so at 11 degrees, that's a 0.4 inch offset at the top. It seems there must be some slip somewhere to keep accumulating but it's only in one direction and on one axis and very consistent, meaning straight sides are very straight but slanted.

Obviously I'm stumped.

 

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The only "true" way to check if the pulleys are properly secured is by putting a mark on them and on the axes, and see if they do not move independently. The pulleys can feel secured but could be a tiny bit lose, as you only have a tiny bit of slanting.

 

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I had the exact same problem on my X motor. I head scratched about it for hours until I noticed the X motor belt was twisting due to lightly touching the rear wood panel. I added washers to the existing black plastic spacers for the motor mount (and also mounted the x motor pulley as close to the motor as I could without it touching - maybe .5 mm?) and the slanting problem went away!

By the way the slanting is caused by missed steps in the X motor servo.

 

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Thanks to all. I got it solved because of this forum. It was a friction issue in the x-drive, like gr5's problem but with a different reason. My x rod drive pulley was mounted 1/2 mm to far down the shaft. Since the pulley rides on the race of the rod bearing, this allowed more of the rod to protrude from the bearing and rub on the end plate. Moving the pulley slightly took care of it.

Thinking the slant over, it's surprising how infrequent I was missing steps. An 11 degree angle is 0.2 radians meaning I was missing a single additional step in the +x direction every 5 layers to make the pattern skew to the negative x.

 

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I'm sure it was missing a partial step on every layer to be that consistent. I think these servos are driven in 1/8 step increments maybe? Does that make sense?

You could have also fixed it by lowering "jerk" and acceleration to ridiculously low values.

 

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