Nozzle scratches on bed/printed layers-.-

Hi,

I recently build myself a Delta Printer (i already haven ultimaker, was just curious to have another) which is printing almost fine, test cubes come out in right dimensions, z height is even all over the printing surface.

there's just one problem left that i couldn't solve: when the nozzle is leveled over the print surface with .1mm height (using a piece of paper) and then moves, i can hear the tip of the nozzle scratch on the printing surface. when the move is finished the paper test shows me that z height is still the same, the problem just occurs while moving. this causes the nozzle to scratch over the printed object, sometimes ruining the first layer, and over time "collecting" print material at the tip of the nozzle, whichs drips off when too much and causing an ugly "burned-looking" drop. sometimes the drop gets pushed away by the passing nozzle, sometimes the nozzle crashes into it an corruptes the next printing moves.

this behavour continues over the whole print, also at higher z values. height of finished prints is correct, so my steps/mm should be right. reducind material extrusion doesnt solve the problem, just causes "unconnected" lines when reduced too far, and the scratching problem remains.....

Still couldnt find a solution to this, after hours of trying i ended up that it must be something with the 3 carriages. something about their movement timing....? But no idea how to influence this.

So my question is: has anyone of you experienced such a thing or an idea what it could cause/solve?



Thanks,

eagreen

Disclaimer: Never used a delta bot.

It sounds to me like your nozzle is moving vertically while trying to move horizontally. There are two things that could cause this. One is bad calibration. If your delta_radius is set wrong you will get the effector moving in either a cup- or dome-shaped pattern instead of flat. Check your calibration, and make sure the nozzle is a paper's width from the bed everywhere -- all sides and the middle.

The second possibility is that you simply have play in your machine. This is harder to fix, but easier to check: with the steppers turned on, and the effector away from the plate, grab the effector and jiggle it. It should be easy to tell if there's play in the vertical axis.

If neither of those is the cause, I'm not sure what it could be, but there's one way you could check. Find a video camera that can record at highish speed, put it close to the effector, and film moving the effector (printing or just jogging) and then play the video back frame-by-frame. You should see some sort of vertical motion in the nozzle, and by looking at how everything else moves, you might be able to figure out what's going on.

I the same symptom on my Delta caused by extruder motor noise in the end stops.
In Repetier at least this causes the current move to end early and the machine looses position.
If you are using Repetier try:
#define ALWAYS_CHECK_ENDSTOPS false

Problem still persists, but im pretty sure now its a hardware problem. when im calibrating the bed with paper, the first spot is perfect, move 2 mm -> too low, move 2 more mm -> perfect, move 2 more -> too high and so on .... :/

also saw some strange behaviour on a test print :

[www.youtube.com]

the nozzle crosses the last printed line when moving closer to the camera, almost looks like it jumps left of it at some point... coulndt find the error yet but still looking

thank you so far

check your belt tension. i bet one of the belts is loose, causing the slight wobble from lag in movement, this effects the machine laterally, and vertically.

checked and no play on any belt an im getting desperate :/
when im homing all axes and move directly to one of the 4 calibration points the height is perfekt. redoin it at slower speed its about .1 to .2mm too low.

homing and goint to x0 y0 z0 -> perfect height, then move directly to third tower base (about x55 y0 z0) -> perfect height, direct move back to center -> .4mm too low (if it would be a loose belt i would be able to move the paper under the nozzle, but the nozzle is pushed hard into it and only movable after lifting the nozzle .4mm)

doing the same with the 2nd tower ( x-55 y-32 z0) the paper gets stuck at the tower and free again after moving back to center. almost fells like the nozzle is keeping height when moving in positive x/y direction and moving down when moving in negative x/y direction.....

If it is regular with about 2 mm period then it looks like pulleys do not match belts?
But the fact that moving horizontaly from center to a side and back results in different height in the center would indicate either motors skipping steps or noise in endstops and you do not have ENDSTOPS_ONLY_FOR_HOMING defined.
Or maybe a pulley is slipping on the motor shaft?

Are you using Marlin? Which flavor? I was able to decrease the homing speed considerably and have a much better time with the bed being level consistently. I'm using Rich Cattel's Marlin fork which I cannot recommend more if you're building something custom.

I've been building a custom Delta by myself and will testify that it is one of the most intensely challenging things I've ever done. So many sleepless nights spent working out engineering problems I had no business taking on alone.

How are your belts positioned? Are they parallel with the bearing carriages? I mean, is there a nice clean path for the belts to travel with the carriages?

I was having a lot of trouble with my endstops having even the slightest bit of wiggle. We're talking .01 mm here when trying to get sexy with that bed.

Problem seems solved, thank you all

rebuild it completely and discovered that in one pulley the tightening screw was not completely tight! just half a turn so the pulley looked like following the motor rotation perfectly but it slipped just a little bit when the motor changed direction. also couldnt see this from outside because the pulley covered the motor axis completely. been looking desperately for the problem for more than 2 months and now its just that little creepy screw

thank you all again for the help an all the suggestions !