Delta printer calibration procedure

ArekRucki

@Phaedrux Thanks.
Could you please look at this procedure? As I wrote before I would print clay
and change print bed very often.

turn on the printer
run autocalibration
do not home
start print
when the print is finished change the build plate
home the printer
run autocalibration and start new print?

Do I need to save the autocalibration results evertytime in this case?
Do I need to home in point 6?

Phaedrux

You'd still want to home the delta towers first (G28 aka homedelta.g) and then do a delta calibration (G32 aka bed.g) before starting the print. Doing the delta calibration without a probe would be pretty tedious. Using a delta without a probe is not recommended.

You can save the calibration between prints, but if the bed surface is changing, then you're likely going to need to re-run it.

ArekRucki

@Phaedrux Sorry for such simple questions. I read "Calibrating a delta printer" in user manual
1000 times and read lot of forum threads but I am totally new on this field.
So I command G28, then G32, then save? And everytime I run new G32 the "fresh" results will override the saved ones, right? Till I reboot my Duet, right?
And for saving should I use this procedure:?
If you are running firmware 1.17 or later, you can run M500 to save new M665 and M666 commands in the config-override.g file. Then, if you have an M501 command at the end of your config.g file, it will run config-override.g at that point, so that the new commands override the ones earlier in your config.g file.
Many, many thanks...

Phaedrux

Since these commands are just macros, or text files containing multiple commands, you can simplify things a bit.

bed.g gets called by G32. So within that file you can have it home first, do the calibration points, then save the results. Using your posted file above as example


; bed.g
; called to perform automatic delta calibration via G32
;
; generated by RepRapFirmware Configuration Tool v3.3.16 on Sat Apr 15 2023 11:44:38 GMT+0200 (czas środkowoeuropejski letni)
M561 ; clear any bed transform
; Probe the bed at 3 peripheral and 3 halfway points, and perform 6-factor auto compensation
; Before running this, you should have set up your Z-probe trigger height to suit your build, in the G31 command in config.g.
G28 ; home the delta towers
G30 P0 X0 Y84.9 H0 Z-99999
G30 P1 X73.53 Y-42.45 H0 Z-99999
G30 P2 X-73.53 Y-42.45 H0 Z-99999
G30 P3 X0 Y42.4 H0 Z-99999
G30 P4 X36.72 Y-21.2 H0 Z-99999
G30 P5 X-36.72 Y-21.2 H0 Z-99999
G30 P6 X0 Y0 H0 Z-99999 S6
M500 ; save the results
; Use S-1 for measurements only, without calculations. Use S4 for endstop heights and Z-height only. Use S6 for full 6 factors
; If your Z probe has significantly different trigger heights depending on XY position, adjust the H parameters in the G30 commands accordingly. The value of each H parameter should be (trigger height at that XY position) - (trigger height at centre of bed)

Then all you would need to do is send G32 to run bed.g and it will home the towers, calibrate, and save the results.

However, as I said above, if you're changing the build surface, you would likely need to re-run the calibration before every print anyway, so the saving portion isn't really important.

And the calibration without a probe isn't very practical.

nikscha

@ArekRucki It's me again ^^
I'm not sure about this procedure, because it only works if you can probe on the buildsurface which in your case will be made of clay. You COULD run autocalibration on it IFF it's parallel to the buildplate. And even then you can't use a method that touches the buildsurface because the soft clay would probably deform. The IR sensor could work, or maybe an inductive probe that senses the metal underneath the clay. But even then it probably won't! The whole point of autocalibration goes away. You should run autocalibration on a surface that is part of the printers frame. That's because autocalibration will set parameters like length of the delta arms, homed height, or even scew of the towers, depending on the parameter.

Considering that it's a clay printer I assume that accuracy isn't crucial? Because then I would do without autocalibration if I were you and instead just measure the delta parameters as accurately as you can. It's not so hard, you probably know the length of your arms as well the distance between them?

I propose the following procedure:

turn on printer
home
place clay on printbed
move printhead down until nozzle touches clay
send G92 ZO
start print
remove print
home
place clay on printbed
move head down until nozzle touches clay
send G92 Z0
etc

If you insist on autocalibration on clay:
The S parameter of G30 has to be 3!
Use a probe that doesn't touch the clay (IR probe?)
Get the clay as even as possible!
Many probe points to average out unevenness.

Procedure:

start printer
home
place clay
autocalibration on clay
start print
stop print
home
etc

ArekRucki

@Phaedrux Thanks a lot. Now that is clear to me. Have a nice day!

ArekRucki

@nikscha Thanks for your time. I was not very clear. I'd have normal print bed e.g. plywood or plaster board. I think both of it have fairly even sufrace. The material I'd print with is clay.
But yes, I need to change the plates every print so they can differ in few milimeters each other.
So I will buy a z probe as @Phaedrux suggests. I still not sure which one. As I wrote few post above it could easily get dirty with clay. For now I'd bet on BL Touch.

Phaedrux

@ArekRucki said in Delta printer calibration procedure:

I still not sure which one.

I suggested a detachable probe, something like this.

https://www.amazon.ca/Printer-Precision-Z-Probe-Leveling-nozzles/dp/B07V6GR72Q

dc42

@ArekRucki said in Delta printer calibration procedure:

But yes, I need to change the plates every print so they can differ in few milimeters

If the plates are flat but the thickness varies then I suggest the following:

Calibrate the printer just once (without a probe) to establish the delta radius and endstop corrections. Save the result.
Before each print, after homing command the nozzle to a few mm above bed centre and execute G30. This will account for the bed thickness having changed.
Ensure that your slicer start GCode does not home the printer at the start.

ArekRucki

@dc42 OK. Thank you.
But now I've examined one of my build plates by touching it with the nozzle in different points and get values from 14,30 to 15,15. I guess the whole bed is a bit tilted. It gives 0,85 mm difference. I don't know it it is big... So when I go with G32 for the very first time with 6-factor calibration and save the results will it eliminate these differences? Or somwhere in higher parts the nozzle will hit the bed?

dc42

@ArekRucki if the bed is tilted wrt the towers then running 6 factor calibration once and saving the result will correct for it. OTOH if the problem is that the bed plates vary in thickness from one side to the other, you will need to recalibrate every time you change the bed plate.

nikscha

@dc42 @ArekRucki or if reuse the same bed plate but rotate it*

nikscha

@ArekRucki said in Delta printer calibration procedure:

@nikscha Thanks for your time. I was not very clear. I'd have normal print bed e.g. plywood or plaster board. I think both of it have fairly even sufrace. The material I'd print with is clay.
But yes, I need to change the plates every print so they can differ in few milimeters each other.
So I will buy a z probe as @Phaedrux suggests. I still not sure which one. As I wrote few post above it could easily get dirty with clay. For now I'd bet on BL Touch.

I see, that makes more sense now thanks for clarifying!
Yeah, BLtouch seems like a good option then! Is it also possible to print on a metal surface with clay? If so, then an inductive probe could be used which prevents inaccuracies from the clay residue on the printbed.

dc42

@nikscha for delta printers, nozzle contact probes are highly recommended. This is because an XY offset of the probe from the nozzle means that if the effector tilt varies even slightly with effector XY position, the effective trigger height of the probe will vary and mess up calibration.

ArekRucki

@dc42
I've just bought BL Touch.
There is in Duet3d manual: Adding trigger height corrections to the bed.g file
What is this actually for? I'd guess one need to do those corrections when there are
any points on bed surface that falls out of probe effective trigger height?
For BL Touch it is from 2,3 to 4,3 mm. So when all the bed is in this range I don't need to do it?

nikscha

@dc42 right, good point!

@ArekRucki (assuming you don't use the nozzle for probing,) the nozzle and the probe aren't the same thing. What you want to know is the distance between the nozzle and the bed, but what you get from probing is the distance between the probe and the bed (obviously ^^). Now most of the time the two are the same (well not the same maybe but they're consistent). But there are some circumstances where (depending on the XY location) the difference differs. One prominent example is effector tilt, mentioned by dc42 earlier. This means that the "plane" on which the arms attach and the hotend and probe is located can have a slight tilt depending on XY location.

If your delta is well build, then you shouldn't have to worry about it.

ArekRucki

@dc42 @nikscha
Many thanks for your help.
Heading for next step of calibration...