First off a couple of questions

1. I sit possible that having the belt on the drive too tight could cause the motor to stall and lose steps?

2. If so, is it possible that the belt could have gotten tighter on it's own?

Now on to the story.

I got my machine setup back at the end of April and after working out a few kinks it ran great, I got all of the material I had on hand cut up in about 2 weeks, and haven't needed to cut any more until this last Sunday. The material I cut is .062 canvas reinforced phenolic sheet, I cut it in stacks of 8 with a 1/4in downcut spiral at 85 ipm, 5 passes plus a full thickness finish pass.

When I went to cut some Sunday I was getting a lot of last steps, only on the x axis, which for my machine is the cross gantry axis. It seemed to get worse with every pass, and seemed to go away for a bit if I let the machine pause and cool down every quarter of a sheet or so, about 5 min of cutting. I was running late at the time so I just did what I had to to get enough made to get through the end of this week so I could do some troubleshooting. I was thinking it was heat in either a motor or drive. It is the plug and play nema 23 kit from CRP, so gecko 540. I have the gecko heatsinked and plenty of airfloiw in my electronics box. Though the last time I cut It was 70-75 degrees and now that summer has actually hit it is 95+ in the shop.

Today I started by cutting through the program without a bit in the machine or the router/dust collection running. I noticed almost immediately a clunking every time the machine would pass a certain point while moving left to right, but not right to left. Didn’t' notice this Sunday, but between the router, cutting noise and dust collection it was probably inaudible. After it finished the machine was off by at least 1/4 inch, and when I could really feel the chunk of motor stalling when I jogged the machine slowly. Always in the same place during travel, and only when moving left to right.

So my first thought was something with the rails, I disconnected the drive from the rack and slid the z axis plate back and forth on the gantry, it was nice and smooth and easy. I reconnected the drive and it was still doing it, was even in exactly the same spot, despite the rack to motor position now being different. I disconnected and moved the drive down a few inches again just to be sure, and it was acting up in the same spot again, even went so far as to loosen the rack and slide it down the beam a few inches. Made no difference.

Next I wanted to eliminate the motor drive in the Gecko so I swapped the cable from the z axis with the one for the x, this made no difference, in my mind ruling out a problem with the gecko drive. So I removed the rack and pinion drive completely and checked to make sure everything was tight. When I went to reinstall it, I decided to swap the drive./motor unit with the one on the y axis. This was when I noticed that it was decidedly more difficult to turn this drive by hand than it was the one on the y-axis. This made a difference, now the x-axis was smooth as silk, and the y-axis was screwing up. It was hard to tell if it was exactly the same type since once the y gets a little out of whack it is constantly trying to pull itself back square.

So at this point I knew it was somewhere in the rack drive/motor pair. So I swapped the motors around, now the known good rack and suspected motor was on y, and the suspected rack and known good motor were on x. This time the x would barely move, stalling almost all the time. I took it back off and checked the bearing for the gears the engage the rack/belt, it spun freely no grinding or anything out of the ordinary. I then realized that I had forgotten a step when I put it together last time, I forgot to snug the motor bolts up before tightening the belt, so when I tightened the motor up it pulled the belt much tighter. I reset it so that the belt was just tight enough to not have slack, but the drive would turn pretty easily. Reinstalled the drive unit, and now it seems to work flawlessly, ran it through the program twice before it was too late and it didn’t lose a step at all.

So I am at a loss, only thing I can think of was the belt was too tight adding a bunch of friction causing the motor to bind up, but why would it always be in the same spot with regards to the rack. Also why would it only start this now if that was the problem.

I am going to try cutting some actual material in the next couple of days, as soon as I get some time.