Extruder scratching on bed, what do I do wrong?

monster

Hi,

I thought I'm at that state that I could test print some simple object. Tried few times, each time extruder goes right 0 on printer bed.
Below I quote my homez.g
Config.g is attached also config.txt

What I did (and not did):

not leveled bed (as I'd love to come up with some script macros that would move heads clockwise (and counter clockwise) over the bed to help me leveling it, but I didn't yet figure out how do I do and run such scripts). But that shouldn't be too much of big deal as I print 2cm diameter test print over the area where z-homing end switch is located.
I do not have z-probe (to be honest I even don't know what is z probing and why).
homing of Z bound to XY homing as bed has magnet in center so that for Z homing I must bring heads over that center spot and lift bed up until reed closes.
now z homing configured so that z home triggered when there is few mm distance between bed and extruders - I thought it would be ok because there is this setting to compensate it: G92 Z5.0
I've started with G92 Z6.0 and I got extruder rinning 0mm (visual accuracy) over the bed.
Changed it to 5.5 - same
Changed to G92 Z5.0 - same (all the time (visual accuracy ofc)
What do I do wrong?

P.S. to defend my z-probing ignorance - though was if printer homes stably and it knows distance between z home and nozzle (6mm) then it should be able to operate correctly.

; homez.g
; called to home the Z axis
;
; generated by RepRapFirmware Configuration Tool v2.1.8 on Mon Mar 30 2020 01:10:04 GMT+0300 (Eastern European Summer Time)

M98 P"quickhomexy.g"
G90              ; absolute positioning
G1 H2 X150 Y150 Z10 F2400  ; move quickly to X and Y axis middle (where Z home trigger is)
;G1 H2 Z10 F2000    ; move quickly to 10cm away from expected home
G91               ; relative positioning
G1 H1 Z-200 F500 ; move Z down until the endstop is triggered
;G92 Z0            		; set Z position to axis minimum (you may want to adjust this)
G92 Z5.0					; tell the firmware that we are at Z=6mm

; Uncomment the following lines to lift Z after probing
G91              ; relative positioning
G1 Z10 F2000       ; lift Z relative to current position
G90              ; absolute positioning

Phaedrux

Your homing method should work. Using G92 Z to set the actual height of the nozzle above the bed after triggering the endstop is a common way to do it.

Not sure exactly what's going on in your case though. Having an accurate way to measure the distance between bed and nozzle would be helpful.

A few questions:

Can you post a few photos of the printer? Can be helpful when dealing with conversions of lesser known printers.
How are you measuring the height of the nozzle above the bed?
How sure are you that M92 Z1060.00 is the correct steps per mm for the Z axis? If you tell it to move 10mm does it actually move 10mm when measured?

M98 P"quickhomexy.g"

Instead of this, you should probably use G28 XY to call the homex and homey files. Homing from a macro with M98 may have unintended consequences.

With regards to probing, the value in it is that the probe is attached to the print head and so can be moved to many points in the XY plane, which can be used to generate a detailed terrain map of the bed surface. It also automates an accurate way of finding the exact Z0 location of the bed surface. It's useful, but not strictly required.

Furthermore, you don't even need additional hardware to use the probing function. RRF has a probeless probing method which prompts you with a jogging dialogue to move the nozzle to just touch the bed and therefore set Z0.

In your config.g you already have this configured

; Z-Probe
M558 P0 H5 F120 T6000                           ; disable Z probe but set dive height, probe speed and travel speed
M557 X15:215 Y15:195 S20                        ; define mesh grid

M558 P0 sets the manual probing.

If you were to send a G30 when your print head is the center of the bed you will be prompted to jog the nozzle down and set Z0. IF you wanted to use this method in your homeall, you would just replace this

G1 H1 Z-200 F500 ; move Z down until the endstop is triggered
;G92 Z0            		; set Z position to axis minimum (you may want to adjust this)
G92 Z5.0					; tell the firmware that we are at Z=6mm

with G30.

monster

@Phaedrux said in Extruder scratching on bed, what do I do wrong?:

A few questions:

Can you post a few photos of the printer? Can be helpful when dealing with conversions of lesser known printers.

I was afraid of it as this "thing" is so untidy and look like pre-historic prototype. But you wont tell anyone then here we go

Obviously my goal is to make it work more less and then make it tidy. Also some parts replacement is still being delivered so I'll a) replace worn off 12mm guide rails to newer once and same with bearing blocks. b) I'll introduce second ball screw for Z axis.

How are you measuring the height of the nozzle above the bed?

Well after homing I give a bed +10 move. Then after homing I use "M564 S0 H0" that will allow me go below zero. And then I go -10 and do -0.5 and count mm's until z motor skips.
Not very scientific but

How sure are you that M92 Z1060.00 is the correct steps per mm for the Z axis? If you tell it to move 10mm does it actually move 10mm when measured?

To begin with my though "number one" was that there must be a cheat page where this data would be present. Cause most of steppers do not big angles per step and there is not too big amount of different pulley's and lead screws. But I didn't come across any. And so I did simple and not terribly accurate experiments:

set some setting in config
tell bed go 20cm
measure actual travel using ruler.
if distance traveled != 20 adjust and go 1.
I got it as accurate as "eye accuracy" per 20cm travel.
So I'd say this shouldn't be a factor for beginning to print problem as here it moves only 1+ cm. So let's say my "eye accuracy" would be +-0.2mm off in 20cm move then for moving 1cm that error shouldn't play too big role I guess?

M98 P

Instead of this, you should probably use G28 XY to call the homex and homey files. Homing from a macro with M98 may have unintended consequences.

Ideas was that "quickhomexy.g" does movement on both axis's at same time - kinda save time. Of course homex and homey exist and do pretty much same as homexy but per axis.

With regards to probing, the value in it is that the probe is attached to the print head and so can be moved to many points in the XY plane, which can be used to generate a detailed terrain map of the bed surface. It also automates an accurate way of finding the exact Z0 location of the bed surface. It's useful, but not strictly required.

Very advanced. I guess I get it one day!

Furthermore, you don't even need additional hardware to use the probing function. RRF has a probeless probing method which prompts you with a jogging dialogue to move the nozzle to just touch the bed and therefore set Z0.

In your config.g you already have this configured
; Z-Probe
M558 P0 H5 F120 T6000                           ; disable Z probe but set dive height, probe speed and travel speed
M557 X15:215 Y15:195 S20                        ; define mesh grid

I must admit these lines came from configurator and I didn't change them at all and not understand them yet. I had just naive hope that doesn't affect any of my homing and and "very scientific" measurements

M558 P0 sets the manual probing.

If you were to send a G30 when your print head is the center of the bed you will be prompted to jog the nozzle down and set Z0. IF you wanted to use this method in your homeall, you would just replace this
G1 H1 Z-200 F500 ; move Z down until the endstop is triggered
;G92 Z0            		; set Z position to axis minimum (you may want to adjust this)
G92 Z5.0					; tell the firmware that we are at Z=6mm
with G30.

This part of wisdom I think I need to process slowly - perhaps reading up what is G30 will help

Phaedrux

G30 tells the firmware to do a probe move at the current location.

For getting the correct steps per mm you can use some formulas if you know the values. For the belt and pulleys you can count teeth.

You can use this calculator: https://docs.google.com/spreadsheets/d/1ts5fz73JQoQ4G0Z95nzfPDSS6HYEyczyZyccDZ5M6B4/edit?usp=sharing

monster

After leveling of the bed I kinda tend to say "yeah some magic of z probing soudns like a good idea"
Apparently my be bit bent, still printable but not ideal...

Phaedrux

https://duet3d.dozuki.com/Wiki/Using_mesh_bed_compensation

That's exactly what mesh compensation is good at.. compensating for.