[1armsbandit]

Hi guys,
I'm running two acme lead screws 2/10 5 starts on my x axis, so I have two steppers one on each of the lead screws. I calibrate the X axis and put the value in for the A axis which is slaved to the x, so they both have the same value in turn they should move together. I think I've always had a problem with it but it's racking real bad and of course it effects what your cutting. I have pressed fit bearing for support at the end of each lead screw. I've been up and down and all around what to tighten and loosen and calibrate. I can't seem to fix it, so any suggestions on how to fix this issue? I have added some pics of when it was first completed, but you get the idea from the pictures what the gantry looks like. Thanks in advance.

[harryn]

I suspect that what you have is not so much "racking" but "tipping". Consider to spread the X axis bearings further apart and have 2 on both the bottom and top. One way to test this is to try pushing on the very top of the X axis one side with about 100 Lbs of force and see what happens. That might seem like a lot, but that is very close to what the lever action there is experiencing when the Z is extended down.

[1armsbandit]

Tipping? Would mean that it want to fall over or something like that? The picture of the machine is not the current state of what it looks like. I've cut the legs shorter to make it my stable and have shorten the z travel. What I was trying to show in the picture was the two lead screws in position on the machine. It's racking because the one is trying to get in front of the other, when I'm just jogging it in place, with out cutting any material. Thanks for your thoughts.

[ger21]

What motors, drives, and power supply are you using?
WHat are your accel and velocity settings?

[1armsbandit]

Motors are 425 oz from Xylotex along with the power supply and one driver board for four motors . Settings are not high accel is set at 50 Velocity set at 60, steps are calibrated to 3221.801932.

[ger21]

I'd say that your accel is set way too high for a Xylotex. I use a Xylotex with 1/2-8 2 start, and 253oz motors (with dampers on them). My slaved motors run at 150ipm, but I have the accel set to 10. Anything higher and it was unreliable.
WHile your motors have twice the torque, your screws have half the mechanical advantage, so things should be fairly equal.

On my Z axis with no damper, I have to keep the accel at 5 or it loses steps.

[1armsbandit]

Thank you for your comments, it had me look at the accel settings; and I have played around changing them with my issue of racking. I couldn't see no change or advantage in lowering the value. I have discovered that the collar that holds the end of the lead screw and the motor was slipping, so I changed it out. It seems to have helped the problem. What I do is jog the machine into say half of my total travel distance in the "X", then I break out the tape measure and measure my gantry on end and the other, if there is a difference I know the machine is racking. When I'm cutting material that's .750 thick I have to make four passes to get threw the material. If I see steps in the second pass, or any that follow then the machine is racking it not consistent in the "x" or possibly the "y" travel. The "y" only has one motor, so less likely to have an issue. Your machine able to run 150ipm, depends on how big it is as well the matieral it's made out of. I run 15ipm on thick material and more on thin stuff. I will try to lower the accel on my next cut to half it's value to see if that inproves the cutting. Thank you again for your comments.
Bandit

[ger21]

Your machine able to run 150ipm, depends on how big it is as well the matieral it's made out of.

It has a cutting area of 30x45, and it's made out of mdf and plywood, with skate bearings on pipe.

[1armsbandit]

I tried a lot lower value in the accel and it really made a big difference in my cut. Your accel is set at 10 what do you have your velocity set at?

[ger21]

155 on my X axis with slaved motors, and 190 on my Y axis.
Any faster an they'll stall occasionally. I've found these settings to be 100% reliable. But every machine is different.

[victorofga]

you can try to using two belt and one motor on the middle,, so if you lose steps you lose on both side... racking eliminated totally..

[1armsbandit]

Thanks Gerry for all your input. Couple more questions, can I see a pic of your machine? Plus how did you make your dampers? What's the advantage to them, could I benefit by having them on my machine. Lastly I use 90 degree aluminum for my v bearings to ride on for my travel. I've files a angle on them to make a point, there not very good done by hand. Have you herd of anybody's idea's of how to get them filed better?