JanetTX:
Any chance we can get a few photos to give context?
Below is a somewhat boring bit about how I'd figure it out.
In the end, it seems like the "best" of the below is to jog about an inch in the "good" direction, and check for anything on the newly-exposed leadscrew; maybe there's something that was inside the anti-backlash nut (causing the problem) when you checked it before. If you see nothing, will the machine go back that full inch in the bad direction? If we're lucky, whatever's doing the damage will drop out. If you can't go back the full inch in the bad direction, that means the blocking chunk is still inside the leadscrew follower (anti-backlash) nut. (See the very end, under "you've now fully disassembled your machine....")
Or, you could have a truly, badly worn anti-backlash nut (they're made of plastic) that's been run into the ends far too many times, and it's days are now over
. That's unlikely, but fits the symptoms.
But really, if the motor is grinding, and you can tell there are significant forces being opposed, then something is blocking or binding somewhere, or a bearing has failed really REALLY badly. There is just too much force involved for it to be relatively-small and relatively-soft things like wood chips. Even pound after pound of aluminum chips have never bothered my machine's movement, and I don't clean it until the chips stand about 2" deep. So there must be something significant being unkind.
Thom
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This is the longer boring part
Because sharkcutup will point at this post and roll his eyes if I don't say this (luv ya, man! ) inspecting the machine, especially under the bed, while it is moving and you know it's broken somehow, is NOT a normal or safe thing to do. Be VERY careful the gantry doesn't clock you upside the head or break your nose or pull out a hank of hair!
To clean that leadscrew I use a light-oil soaked chip brush taped to a ruler. I chase the gantry assembly with the brush as I jog it. Maybe for next time when it DOES move again
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It sounds like you've verified there aren't any tubes or wires anywhere being pulled.
It sounds like you're not hitting a broken limit switch, because that would make the motors stop pushing, and they're still pushing.
Like everyone else, it sure sounds like something to do with the undercarriage of the machine, under the extruded aluminum sectioned bed.
Any chance there's something blocking the movement of the vertical gantry arms along the rails? Like a screwdriver or a piece of wood
just out of visual range behind the slide rail? Outside? Like one of those thin steel rulers? Or a pen?
As the machine currently sits, can you jog it just a tiny bit in the NON-binding direction? Does it move okay? Can you go an inch?
If you can go an inch in the good direction, can you then go back that full inch in the bad direction? Or can you go LESS (or more) than that inch?
If it will only move a little bit back from the one-inch-to-the-good location, I'd suspect a REALLY loose coupler that's getting jammed.
Check under the aluminum top (get a flashlight, so you can get a really good look), that the end of the leadscrew looks like it's in the bearing pocket okay.
Check the four bolts holding the stepper motor on. If they're loose, this could be a pain to fix, since holding those nuts way under there might mean getting or making a really long wrench.
Or worse, taking the aluminum bed apart.
I don't know if your arms will fit underneath, but are you able to manually turn the leadscrew and watch it move? I suppose a long push-stick from each side, hitting on the exposed coupler bolts might work. See if you get the same level of resistance that the motor is claiming. If not, then a jammed or very loose coupler might be an issue.
So, check there's no debris stuck back into the motor-to-leadscrew coupler hole...Kinda grasping at straws here, since the coupler screws would normally be expected to clear that pocket.
If none of those things turn up something, I'm going to say: there has to be something stuck in the mechanism that's preventing movement. Either something blocking it physically. Even if the side-rail bearings had a broken ball, it would still slide, you'd just hear a grinding sound. To check for that means removing the gantry with those dozen bolts on the side.
And if it's not in the rails, then it has to be in the stepper / lead screw / follower. If you've gotten to the point that you've taken off the gantry and still nothing, then the aluminum bed will have to come off, so you have have some direct access to the ornery bits. Once inside there, there's not a lot. If you can't see anything in the leadscrew, the non-driven end is solidly in the bearing pocket, and the motor coupling is aligned and tightened properly with nothing in that pocket, then my guess would be something has lodged inside the follower (anti-backlash nut) assembly. That will be another heaping mess of disassembly, but once you find the chip, you'll probably want to just go ahead and put in a new anti-backlash nut, available on their web site.
Really, once you've gotten the machine torn down that far, there's nothing else to it, so you will have found it. Hopefully you'll find the blocking issue WAY early in the process.
Regards,
Thom
P.S. I know kinda how you feel with insane problems that just should not exist: when I first got mine, I tried to get it running on the dining room table before moving it to the basement, due to the narrow stairs. 4.5 MONTHS later it still wasn't working reliably, but was still occupying the dining room table! Only a replacement controller eventually improved the reliability enough to make it usable. It's NEVER been 100%, though.