y-axis jerk

[DickB]

My machine started misbehaving while going through the setup procedures, swapping bits and finding the surface etc. When the head moves rather rapidly over to the bit plate and back, the head will jerk in the y-direction. Sometimes it appears to hesitate; sometimes it actually reverses direction for a bit and then continues normally. I ran a carve after it started doing this, and it carved fine. I did not see any jerking while the carve was in progress. But a 3-pass cutout in pine, which I have done successfully many times, resulted in a broken bit. Of course if it jerked while cutting the bit would snap.

I have checked and cleaned the y-axis encoder and replaced the bearings. The gears look good. The belt is clean and tension is set properly. The rails are clean. I checked tightness of the bearings. They seem to run smoothly when the head is pushed by hand.

I suspect a power problem, cables or connectors, or the y-axis motor itself. I'd appreciate any help or insight before I start replacing parts.

[Digitalwoodshop]

So you DID change the 2 bearings inside the gearbox as that would be the first thing.... That is Good...

Second is look at the mounting of the motor in the U shaped frame.... If the big plastic gear rubs in the Frame then it will cause this....

A Frozen Bearing is next... Mark the bearing with a marker and move the head....

Scrub the underside of the rails as the flat shoulder on each side of the round rails can get sawdust packed on it..... Sides... I use a small wire brush....

IF the Y motor is bad... You could swap it with the Z..... Motor for motor.... leave the gear boxes where they are for mounting hardware....

But 9 times out of 10.... A worn tapered shaft..... and bad bearings.... I did not think to ask... Did you check to see if the shaft is worn thin? Causing the big plastic gear to rub the frame....

Good Luck,

AL

[DickB]

Thanks for the suggestions. I did replace both bearings - one felt a bit rough and the other was fine, but they both were replaced. Shaft was good. There is plenty of clearance between the plastic gear and the U-frame. I reset the tension of the y-truck bearings and they moved freely when I loosened them during the process. But I also just double-checked visually and they are rotating nicely when the head is moved. I also went to tech support with this - did they change policy? I called four times and no mention of a charge. At their suggestion I reformatted the card, lubricated the rails, reset belt tension, and cleaned the belt tension mechanism. When I told them that I had already removed the encoder cover and cleaned dust out, one tech asked me if the dust was sawdust or a fine black dust. It was the latter. He said that generally means that the encoder wheel rubbed and got damaged. I was wondering why it was black dust this time - it was sawdust the first time, but since I sealed with silicone I haven't seen sawdust in there. On the fourth call I had exhausted all of their suggestions and a new y-axis motor was recommended next and ordered. But maybe while waiting I will try swapping motors and see what happens.

[DickB]

OK, I installed the replacement y-motor and got the same result. I called tech support and the tech checked with an engineer. They both concluded that it must be something mechanical with the belt, idler, spring tension, rails, or bearings - a chip somewhere perhaps. I examined more closely and loosened the y-truck bearings completely so that I could spin each bearing in turn, and I found a bad one. This escaped me before. So the lesson learned is the only way to really know the condition of the bearings is to loosen them and spin them in free air. BTW I also checked the z-truck and found a bad bearing there.

I don't feel too badly about having replaced the motor, because the black dust inside the encoder of the old one spelled trouble to me. I noted that the replacement motor has a gasket for the encoder cover which my original does not.

As a side note, my recent experiences with tech support have been much, much better than in the past. I have spoken to at least 6 different techs on this one problem, and they all seem knowledgeable and have been helpful in troubleshooting this problem step by step. So I must give credit where credit is due.

[HelpBot3000]

Thank you for the compliment, (I'm the one you spoke to). I try to help as best as I can in any way possible. Let me know how everything went either on here or if you prefer, call the support line again. I'm here until 6pm CST.

Barry
Hardware Support

[Digitalwoodshop]

Good Job Barry and CW Team... This is GOOD to know that even marking the bearings with a marker and forcing them to move will not show a bad stuck bearing.... Letting the whole head loose then checking each bearing is a good idea.

AL

[DickB]

Well, a stuck bearing would be detected, but this one is not totally stuck. It is however very rough and won't spin on its own at all.

[DickB]

It was the bearings. Although I ordered replacements, while waiting I decided to try cleaning them. (My son and I used to do this regularly with RC car bearings when we were racing.) That took care of the problem.

OK, not only is my machine back up and running, but I got a very pleasant surprise.

I was making a test run of a new project and loaded a scrap board that was too small, so I knew that I would get a few minutes of "air carve" first. I started this up and went into my office. A few minutes later, my wife comes in and asked what's wrong, why is my machine so quiet? I explain what an air carve is and why, and tell her don't worry, it'll get noisy soon. Well, 5 minutes go by, and I'm thinking, it must have hit the board by now - something is wrong. I go down, and half the pattern has been carved! The machine is running way more quietly, and with less vibration, than ever. Thing is, I don't really know what I did. Since I had to dismantle the y- and z-axis trucks, the only thing I can think of is that something was loose somewhere, and in the process of rebuilding, I got it together better.

I've been having problems drilling accurate 1/8" diameter holes - they come out slightly oval. I'm anxious to give them a try again with my "new" machine.