2nd Post-Gantry goes out of square

[justicedavid65]

I started a thread a few days ago asking questions about my DIY machine and got some help. I'm down to just one issue plaguing me, so I wanted to start a new one.

My machine is 1500mmx1500mm all 1610 ball screw and 15mm linear rails. C Beam on Y axis and dual C Beams on the X. My machine is square, measuring corner to corner both are the same. I can square my gantry by moving it to the front of the machine and touching both side to the front plates (I've attached a picture just so you can see what the design looks like). After squaring I can jog the gantry up and down the full length of the frame many times and everything is fine, but if I run a g code file, 'air cutting' the gantry will get out of square very quickly. I've tried circles and squares and both cause this.

I can't tell which side is causing it, or if it's both sides? I can't hear or see any stalling or loosing steps.

Any ideas? or troubleshooting techniques to figure this out?

Thanks!

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[ger21]

Reduce acceleration and velocity 25%.
If that doesn't help, reduce it again.

[justicedavid65]

Thanks, I've taken it all the way down to 400 vel and 50 accel and still get the same results?

[ger21]

Are those number mm's?

[justicedavid65]

Oh, sorry. Yes mm.

[justicedavid65]

Just for a little more info, I am using 2 48V power supplies, 50V stepper drivers and 420oz motors with 9mh inductance.

[ger21]

Do you have the current set properly on the drives?

[justicedavid65]

Well, I think I do. The motors are 3amp and here is the stepper that I'm using: DQ542MA-Stepping motor,stepper motor,driver supplier,stepper driver manufacturer,Stepper Motor,Drives,Driver

I have them set to RMS 3.00/Peak 4.2, the highest available for the driver. someone in another thread suggested to check the amps coming out of the stepper, but I have no idea how to do that?

Also, I have them set to full current and 1/8 microstepping.

[ger21]

I don't know how to verify the current, but it sounds like it's setup correctly.

Those accel and velocity numbers are pretty low, so the problem is probably something else.

What control software is this?

[justicedavid65]

I'm using GRBL with a CNC XPRO board CNC xPRO V4 Controller - Spark Concepts

And CNCJS software https://cnc.js.org/

Thanks again for your in trying to solve this!

[justicedavid65]

I'm using GRBL with a CNC XPRO board CNC xPRO V4 Controller - Spark Concepts

And CNCJS software https://cnc.js.org/

And one more weird thing I have noticed the past few days. When I first start the machine the right side Y axis won't move. I have to move it manually a few turns, then it will start to move when I jog or run gcode? WEIRD.

Thanks again for your help in trying to solve this!

[ger21]

I don't know anything about GRBL, but I'd be inclined to look at your electronics or software settings.

[vger]

Try swapping the left and right connections to the y motors. If the problem of not moving on startup moves to the other side, the problem is in your drivers or wiring.

[justicedavid65]

So, tonight I took the 2 Y motors off of the frame and put tape on the shafts. I ran a gcode project and they stayed in sync for a while, but then there was a long y axis run and that's where they got out of sync. Just prior to running this code I replaced the 2 y axis drivers with the x and z drivers because I know they were good.

Does this point to one of these motors as the problem?

[fretman_2]

Are you sure your gantry is rigid? Looks like it could use some bracing! If it's square before cutting and not after, then it would seem to me that the process of moving the gantry or z axis is pulling it off. Is your lead screw parallel and in the center of where it should be?

[ger21]

So, tonight I took the 2 Y motors off of the frame and put tape on the shafts. I ran a gcode project and they stayed in sync for a while, but then there was a long y axis run and that's where they got out of sync

Motors just lying on a bench are susceptible to resonance, which can cause lost steps or stalling, if it's bad enough. This may be what you are seeing.

You might want to try some different microstep settings, and see if that makes a difference.

[justicedavid65]

@fretman - This is a design that is being used by several others and no issues with the gantry, so I don't think it's mechanical

@ger21 - Today I connected both Y motors directly to the steppers, no splice at all between motor and stepper. I ran some code and the right motor fell out of sync. Then I switch drivers and the same motor fell out of sync. I don't see how it can be anything except the motor? No wiring issues and the same motor lost steps on different drivers.

[109jb]

Are the main power cables for the drivers wired in a star configuration from the power supply or are they daisy-chained. Should be star configuration.

[justicedavid65]

I have 2 48V power supplies. The mains feeds the first one and it feeds the 2nd one. Both of the Y motors are powered from the 2nd power supply, not daisy chained.

[Ntl]

@fretman - This is a design that is being used by several others and no issues with the gantry, so I don't think it's mechanical

@ger21 - Today I connected both Y motors directly to the steppers, no splice at all between motor and stepper. I ran some code and the right motor fell out of sync. Then I switch drivers and the same motor fell out of sync. I don't see how it can be anything except the motor? No wiring issues and the same motor lost steps on different drivers.

How do the drives connect to the motor? Do you think it could be the connection to the motor is bad? Have you also switched the suspect motor to a different axis to see if it loses steps? Sounds like you found the issue and now you just need to see if it's really a bad motor or maybe a bad connection.