Banding on tall parts
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Ok, so I have now added angle braces to the side to keep the frame from twisting. It is amazing how much it was able to twist before versus after. It didn't change anything however. I also could not spot anything wrong at different heights. One thing I did notice is that after it homes, it drop by 5mm and the head shifts ever so slightly towards one tower. Now I can see one tower almost bounce and another almost drop. Interestingly enough its the two towers correlating to the layer shifting. Now I just have to find the cause for that little shift at the end.
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@bpislife said in Banding on tall parts:
Ok, so I have now added angle braces to the side to keep the frame from twisting. It is amazing how much it was able to twist before versus after. It didn't change anything however. I also could not spot anything wrong at different heights. One thing I did notice is that after it homes, it drop by 5mm and the head shifts ever so slightly towards one tower.
That's normal, it just means that your endstop switches are at slightly different heights and corrections have been applied in the M666 command..
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You're dashing my hopes DC your dashing my hopes.
Seriously thanks for pointing that out, the homedelta file moves to 0,0 at the end so there is that.I am going to continue on the path of replacing things and maybe I will find it. Either that or I will simply build a whole new printer from scratch.
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Did you ever try it without the bed on? I see you mentioned it, but didn't come back and say whether you did or not.
What about printing a tall cylinder in vase mode? Print it pretty fast and it should give you the chance to watch things as the effector goes round and round.
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@number40fan said in Banding on tall parts:
Did you ever try it without the bed on? I see you mentioned it, but didn't come back and say whether you did or not.
I did try with the bed off and it made no difference. I am going to try vase mode that is a great idea. Will let you know. I have new carriages and linear bearings coming as well.
I did notice the wheel at the top of the tower are all very loose, but I don't think that matters as it only allows the belt to roll and doesn't really effect things much. I did also notice the belt on one tower turning in and out as the printer went from lifting the carriage to lowering the carriage. Again with such a large band I suspect its not that directly.
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The twisting of the belt has me worried. It shouldn't do that if under the correct amount of tension. Are the pulleys on top smooth or toothed?
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@number40fan They are smooth. I tend to agree that something doesn't seem right. can you recommend a good pully for the belts on the top? It would explain why putting pressure on them helps,
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Anything that is toothed. Do you have 20 or 16 toothed pulleys on the motors? Are the bolts passing through the upper pulleys 3mm or 5mm? I bought a pack of 5 or maybe 6 from Amazon that were toothed, 3mm through hole and even had a bearing for just a few bucks. Cheapest ones I could find, really, and they worked good.
If the pulleys on the motors are 20 toothed (and looking at your config, they probably are), you might consider getting 16 toothed all the way around. It will up the resolution from 80 to 100 steps/mm.
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@number40fan said in Banding on tall parts:
, 3mm through hole and even had a bearing for just a few bucks. Cheapest ones I could find, really, and they worked good.
If the pulleys on the motors are 20 toothed (and looking at your config, they probably areNice, ok I will take a look. They are 20 teeth right now. The banding is very visible in vase mode but its very hard to pin point. I think that pull may be the issue as there is a ton of play. It is on a 3mm bolt and is free to slide forward and back. It also it does not have teeth so I can see the belt bounce with each movement. Keep in mind I don't think any of that is causing the banding pattern though it is hard to do. I am going to right a macro that just moves slow up and down over the area that bands. Does anyone know how to do "loops" in a macro or am I better off just copying and pasting a ton of gcode repeats manually.
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If you have nothing better to do, you could try twisting the belt a half turn so the smooth side of the belt rides on the smoothness of the idler pulley. Might have to re-tension afterwards.
You'll need to copy and paste the code to get it to repeat.
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So an update in case others face this issue. It turns out that when I was changing the top pulley wheel of the front right tower that it didn't feel smooth when i turned it. I put the belt on it and moved it (disconnected from everything else) and I could feel as if the pulley developed a flat spot, always had it, well whatever it was there. Definitely seems like the culprit. I didn't notice before since I didn't have a new pulley to compare it to. It is subtle but you can feel it. Since I never just do a simple repair, I am upgrading the pulleys on all towers to the 16 tooth version, replacing the linear rails, new carriage, belts, 16 tooth gear on the stepper motors, and since I am essentially rebuilding the entire printer, I am also upgrading the motors to 0.9 degree motors.
So yea I definitely think it was just the pulley, but since I already ordered all the parts I am upgrading everything else.
Once I am done replacing everything and re configuring the printer I will re-run the test and post the progress.
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made all the changes and the banding seemed worse and significantly messier (not perfect shape). I took a closer look at the way I was training the wires and I do believe that caused some issues and will be taking care of that. The majority of the problem however I believe is that the new 16 tooth pulleys (at least the motor side) aren't perfectly round. You can feel it pretty easily. Junk. Anyways I am ordering more but not sure the quality will be any good. Anyone got any good suggestions for high quality 16 tooth pulleys?
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Dang, what brand did you get? The ones I bought were Qunqi, cheapest I could find.
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@number40fan kingprint. This is so odd. The chances of the banding being exactly the same with a whole new drive line make me think it might be the mounts or something related.
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So I just changed the pulley on one motor that made a noticable change in belt tension as I moved the carriage and now i want to see if the banding changes at all or not.
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Success!! After adjusting the pulley on the motor on the X tower I adjusted the pulley on the right tower as well. There were two set screws and I had both torqued down. There was a lot of play between the pulley and the rod without both, but it turns out using both set screws offset the pulley so that its oblong when secured to the motor shaft. After only using 1 set screw on the flat portion on both motors, the major bands are gone. This is the first time I ever printed this tall without those thick bands.
Now the next thing I need to do is clean up the smaller bands on the printer.
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Awesome.
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@number40fan Thanks for your help. So I printed the original part and I am getting banding again. At least it is significantly better and I know where the issue is. Will wait until I get the new pulleys.
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As promised I am going to keep this updated. I completely tore down the printer and put it all back together. In the process I replaced the flat style T-nuts that anycubic use with traditional ones as the flat ones can slide over time. I say this because I noticed a 1mm gap in one extrusion to the corner bracket that wasn't there before. I realized this as I found the top of the circle that had a flat spot that aligned itself with the Y tower. Maybe all the work to swap the PCB with the Duet WiFi I moved it. In any event I squared everything up and replaced the corner brackets with metal ones from RobotDigg.
Here is a picture of the progression. The bottom was with old belts and pulleys, middle is with new belts pulleys, and the top is the latest. You can see it is a lot smoother, but I still can't figure out the banding.
Top picture is the base and the bottom picture is of the top. The bands vary with print time. The first two rods had infill with the latest being printed in vase mode.
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Are you using PID or bang-bang control of the bed heater?
Duet WiFi hardware designer and firmware engineer
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