A couple weeks ago I got my LowRider2 built and was super excited to use it. On the maiden cut I noticed some drifting. For the past two weeks I’ve been trying everything I can think of (lot’s of good suggestions on this forum) but nothing is working. Any suggestions you guys have would be much appreciated.
My Test
The basic test I’m doing is taking a sqaure and marking on the table where it hit’s one of the X tubes. I do that on both sides of the X axis then run it down the Y 500mm and back. I then check the marks, and I’m a 1/4 in off on one side, and pretty close on the other… maybe just a 1/32 off once every 5 trips.
Things I’ve tried
Tightened/Loosened Y belts
Adjusted a Y motor pully - It looked like the belt was rubbing on the top of the pully and maybe pulling it off occasionally
Shimmed the rails to make sure they are strait and parallel
Swapped the Y driver chips to see if one was bad
Rechecked the vref to make sure they are the same (1.34)
Adjusted the X tubes to make sure they are square to the XZ brackets and the distance is the same on both
Checked that I had the Y wheel brackets on correctly
Checked for flex in the Y plates. I’m using 1/2 plywood
Parts I had links but couldn’t post them here due to forum rules
Board - OSOYOO 3D Printer Kit with RAMPS 1.4 Controller + Mega 2560 Board + 5pcs A4988 Stepper Motor Driver with Heatsink + LCD 12864 Graphic Smart Display Controller with Adapter for Arduino RepRap
Motors - STEPPERONLINE 5PCS Nema 17 Stepper Motor Bipolar 2A 84oz.in 48mm 4-Lead for 3D Printer/CNC
Pictures
I have bunch more, but can only post one due to forum rules
My guess it that the wheels are traveling side to side. The Z tubes are probably rubbing, which causes it to stop. There is probably 1/4" between the Z tubes on one side.
I fixed this on mine by putting some 3/4"x3/4" tracks inside the wheels. On my second table, I used 3/4" aluminum angle. Others have used the router to carve a groove for the wheels.
If you find this is the culprit try waxing the side of the rails with paste wax or beeswax and see if that helps. It’ll get you by until you have time for a real fix.
Thanks for the reply @jeffeb3. I had seen others add tracks, but saw more that didn’t need to so I thought I would try to rule out all other things first. But since I had some t-track laying around I thought I would give it a try. I clamped it down temporarily to see if that would make an improvement and doing that brought two issues to light.
Loose XY connection - When laying the track down tight to the wheels, I noticed the track and my rails below it weren’t parallel. I rechecked the gantry for square at the XY bracket, it was square. I double checked the length of the X tubes, they were equal. Then I measured the distance between the Y plates near the wheels and they were out by 1/8 inch. After hunting for the issue, I noticed the front left corner of the XY bracket was a bit loose and allowing the Y plate to move in/out. I tightened that up and ran the test without the track and it was marginally better. Maybe only an 1/8 out instead of 1/4.
Slipping pully - At this point, I clamped the now parallel track in place and ran a test. While moving, the gantry would bind up a lot and was clearly getting stuck. The test was now showing more than an inch out. I tried readjusting the tracks, loosening them, tightening them, use the 1/4in side for height, the 3/4in side for height, nothing cut down on the binding. All the binding got me wondering though about the motor, pully and belt. When the gantry stops, what happens there? Does the belt skip? The motor bind?. So I watched the motor closely when it was moving and saw the issue, the motor shaft was spinning and the pully wasn’t. I knew exactly what the problem was. When bolting on the pully weeks ago, I noticed the shaft’s flat part didn’t go down all the way to where the grub screws needed to go. I just tightened them good on the round shaft and assumed the two would be good enough… guess not.
I’m thinking I can just grind that flat spot down a litter farther on the shaft? I’d hate to screw it up, but a motor is pretty cheap I guess if I do. Any other ideas?
The grub screw needs to be on the flat. Can it fit if you flip the pulley upside down? Some locktite on those are helpful too.
Once all the mechanical stuff is still, the motors themselves will skip steps when you bind. Stepper motors use magnets to hold their place, and they are sort of organized as 12341234124. If something pushes hard enough, it will skip from one ‘2’ to the next ‘2’. Nothing grinds, nothing runs when that happens. It just pops 4 while steps (or 8 or 12). So it sounds like skipping gears (crunch crunch).
I screwed one track down, and then used the wheels to make the opposite side the right length. Then I pushed the gantry to the other end and used the wheels again to choose where to mount the other end of the second track. That kept it from binding. It might make a bit of a parallelogram (by 1/8") but you can adjust the starting place of the gantry to make the other axis perpendicular to that rail and you will cut square (but lose a tiny slice of work area).
That’s what I’d do. The flat spot doesn’t have to match the spot higher up exactly, and doesn’t need to be very deep. If you have a pulley you can scrap, you can also use it as a drill guide and just make a small indent into the shaft…
But a dremel with a grinding disk will make quick work of it. A file and some time will also do an adequate job.
