Z axis issue: wrong movement (layers)

zecchi · 28 Dec 2019, 23:53

Hi,
First of all I want to thanks you all for the support , finally I figure out with the Bl touch issue.
But now there is a problem with Z axis.
Since several days my prints are very bad, it seems there is "Z wobble". In my opinion is not "Z wobble" (see attachment) because the error is all around the object (the error is the same in all faces) as if the nozzle was too stick to the print.

So , I tried a lot of solutions but , unfortunately, nothing worked. I've tried:

verify if rods are parallel to the frame ---> yes, they are . The frame is perfectly square (3030 profiles) and I tested the parallelism with a dial indicator.
verify the movement of X and Y carriages ---> perfect movement, parallel with the frame.
verify stability of the heated bed and temperature ---> bed is rigid , temperature perfect
verify extrusion multiplier ---> ok
verify if the slicer ( prusa slicer ) determinated the problem ---> no , I've tried also with simplify , no differences.
This is my z axis:

Than I've tried to leave the two nuts free to move but nothing change, I've also took off the bearing but nothing change.

And today I've tried to measure with a dial indicator the "Z movement" during print and I've noticed that Z axis moves incorrectly: most of times it does the correct layer height (0.2) and other it does wrong movement (0.26, 0.18, 0.24... )
Tomorrow I'll post my config.g file.

So my questions are:

Should I try something else ?
At the moment the board running a 'RC' firmware (2.04Rc ), should I update it?
It could be a mechanical issue?

Thanks ,
Alex

Veti · 29 Dec 2019, 02:12

@zecchi said in Z axis issue: wrong movement (layers):

At the moment the board running a 'RC' firmware (2.04Rc ), should I update it?

yes. rc firmware are not supported if they are not the latest.

zecchi · 29 Dec 2019, 14:03

@zecchi this is my config.g :

config.g

; Configuration file for Duet WiFi (firmware version 2.03)
; executed by the firmware on start-up
;
; generated by RepRapFirmware Configuration Tool v2.1.4 on Sun Dec 29 2019 12:57:27 GMT+0100 (Ora standard dell’Europa centrale)

; General preferences
G90 ; send absolute coordinates...
M83 ; ...but relative extruder moves
M550 P"ZecchiPrinter" ; set printer name

M667 S1 ; select CoreXY mode

; Network
M551 P"123" ; set password
M552 S1 ; enable network
M586 P0 S1 ; enable HTTP
M586 P1 S0 ; disable FTP
M586 P2 S0 ; disable Telnet

; Drives
M569 P0 S0 ; physical drive 0 goes forwards
M569 P1 S0 ; physical drive 1 goes forwards
M569 P2 S1 ; physical drive 2 goes forwards
M569 P3 S0 ; physical drive 3 goes forwards
M584 X0 Y1 Z2 E3 ; set drive mapping
M350 X16 Y16 Z16 E16 I1 ; configure microstepping with interpolation
M92 X80.00 Y80.00 Z1600.00 E96.56 ; set steps per mm
M566 X720.00 Y720.00 Z30.00 E300.00 ; set maximum instantaneous speed changes (mm/min)
M203 X6000.00 Y6000.00 Z1200.00 E4800.00 ; set maximum speeds (mm/min)
M201 X3000.00 Y3000.00 Z100.00 E4000.00 ; set accelerations (mm/s^2)
M906 X1000 Y1000 Z1000 E1000 I30 ; set motor currents (mA) and motor idle factor in per cent
M84 S30 ; Set idle timeout

; Axis Limits
M208 X0 Y0 Z0 S1 ; set axis minima
M208 X310 Y315 Z315 S0 ; set axis maxima

; Endstops
M574 X2 Y1 S0 ; set active low and disabled endstops
M574 Z2 S2 ; set endstops controlled by probe

; Z-Probe
M558 P5 H5 F120 T6000 ; set Z probe type to switch and the dive height + speeds
G31 P500 X0 Y-58.5 Z2.5 ; set Z probe trigger value, offset and trigger height
M557 X15:300 Y12.5:297.5 S57 ; define mesh grid

; Heaters
M307 H0 B0 S1.00 ; disable bang-bang mode for the bed heater and set PWM limit
M305 P0 T100000 B4138 R4700 ; set thermistor + ADC parameters for heater 0
M143 H0 S80 ; set temperature limit for heater 0 to 80C
M305 P1 T100000 B4138 R4700 ; set thermistor + ADC parameters for heater 1
M143 H1 S250 ; set temperature limit for heater 1 to 250C

; Fans
M106 P0 C"Hotend" S1 I0 F1000 H-1 ; set fan 0 name, value, PWM signal inversion and frequency. Thermostatic control is turned off

; Tools
M563 P0 S"Hotend_0" D0 H1 F0 ; define tool 0
G10 P0 X0 Y0 Z0 ; set tool 0 axis offsets
G10 P0 R0 S0 ; set initial tool 0 active and standby temperatures to 0C

; Custom settings are not defined

; Miscellaneous
M911 S22.5 R23.5 P"M913 X0 Y0 G91 M83 G1 Z3 E-5 F1000" ; set voltage thresholds and actions to run on power loss

Phaedrux · 29 Dec 2019, 18:05

@zecchi said in Z axis issue: wrong movement (layers):

M203 X6000.00 Y6000.00 Z1200.00 E4800.00 ; set maximum speeds (mm/min)

1200 may be a bit too fast for your Z axis. Try reducing it by half. Perhaps it's missing steps or binding. Though this is likely offset by the very low acceleration value.

Can you test the repeatability of your Z axis? Set to a known position marker and then move the z axis up and down many times and see if it returns to the same starting position.

@zecchi said in Z axis issue: wrong movement (layers):

(0.26, 0.18, 0.24... )

What is the full step resolution of your z axis? You show that it's belted to the lead screw. Is there a gear reduction involved? Is the belt slipping the teeth?

The motor current for the Z axis is 1000. What is the rated current of the motor? Ideally you should set the current to be 70-85% of the rated max current of the motor.

You're using anti-backlash nuts. They typically are not necessary on the Z axis since there is constant downward force on the bed from gravity and the bed is always dropping away from the nozzle during a print. They can increase friction however to the point they cause binding.

Have you lubricated the lead screws?

zecchi · 30 Dec 2019, 08:17

@Phaedrux said in Z axis issue: wrong movement (layers):

Can you test the repeatability of your Z axis? Set to a known position marker and then move the z axis up and down many times and see if it returns to the same starting position.

Thanks for your replay.
I'll try later.

zecchi · 30 Dec 2019, 08:21

@Phaedrux said in Z axis issue: wrong movement (layers):

Is there a gear reduction involved?

There is a 1 to 1 ratio

zecchi · 30 Dec 2019, 08:24

@Phaedrux said in Z axis issue: wrong movement (layers):

Is the belt slipping the teeth?

Belts are quite tight, I don't think they can slip (I hope… no noises , nothing that make me to think they are slipping )

zecchi · 30 Dec 2019, 08:27

@Phaedrux said in Z axis issue: wrong movement (layers):

Ideally you should set the current to be 70-85% of the rated max current of the motor.

Ok, it was too low. I set 1200 mA (80% of 1.5A). Unfortunately the error doesn't disappear.

zecchi · 30 Dec 2019, 08:32

@Phaedrux said in Z axis issue: wrong movement (layers):

You're using anti-backlash nuts. They typically are not necessary on the Z axis since there is constant downward force on the bed from gravity and the bed is always dropping away from the nozzle during a print. They can increase friction however to the point they cause binding.
Have you lubricated the lead screws?

I'll try to remove nuts and use normal ones. Also I'll try to clean and re-lubricate the lead screws

zecchi · 1 Jan 2020, 09:19

News:
-Repetitivety Is ok, tested with a dial indicator
-I've change the nut. Some improvements but the error doesn't disappear.

Other advices?

SIam · 1 Jan 2020, 13:06

it looks like a z-wobble dubble (tripple) check the Z-Axis motion this must be stable and run smooth (it can be a nightmare to find the right position)

zecchi · 1 Jan 2020, 16:54

@SIam
I've printed a piece in order to fix the lead screws at the exactly center of the two rods, quite good but I didn't solve the problem.

Any suggestions?

Phaedrux · 1 Jan 2020, 16:56

@zecchi said in Z axis issue: wrong movement (layers):

-I've change the nut. Some improvements but the error doesn't disappear.

Look for more sources of binding. The smooth rods and bearings would be my next target.

zecchi · 3 Jan 2020, 21:44

Also rods are checked. Z axes is absolutely perfect, tested with a dial indicator (only 0.01mm of error in 300mm ). I've also printed a jig in order to have the rods at the same distance.
But , layer are, still, inconstant (0.24, 0.18, 0.22 ecc...) And this cause the blob (I'm pretty sure about that ).

Phaedrux · 3 Jan 2020, 21:48

@Phaedrux said in Z axis issue: wrong movement (layers):

What is the full step resolution of your z axis?

@zecchi What is the pitch/lead of your lead screws?

The problem really seems to be similar to trying to print at a layer height that isn't a multiple of the full step resolution of the Z axis.

https://blog.prusaprinters.org/calculator/#optimallayer

zecchi · 3 Jan 2020, 21:50

@Phaedrux
2mm pitch. (I ordered the 8mm pitch but it arrived wrong).

zecchi · 3 Jan 2020, 21:53

@Phaedrux
I've shorter 8mm pitch lead screws. I'll try with them.

Phaedrux · 3 Jan 2020, 21:58

@zecchi said in Z axis issue: wrong movement (layers):

2mm pitch.

Well there goes that theory.

With a 2mm lead, and 1.8 degree motors (deduced from your 1600 steps per mm on Z) your full step resolution is 0.01mm. So you have no limits there.

What are the motor specs?

zecchi · 3 Jan 2020, 22:11

@Phaedrux
So, if my layer height is 0.2mm isn't a problem, correct?

Motor: 1.5A , 1.8°. Classic 17HS4401 stepper motor.

Phaedrux · 3 Jan 2020, 22:17

@zecchi said in Z axis issue: wrong movement (layers):

@Phaedrux
So, if my layer height is 0.2mm isn't a problem, correct?

Correct