Brand new prusa mini: Z needs to adjust on every new print.  

RE: Brand new prusa mini: Z needs to adjust on every new print.

@wersimo

Now that you have calibrated Z with a preheated MINDA, the workaround should work from now on.

RE: Brand new prusa mini: Z needs to adjust on every new print.

Ok, but I preheated the Minda manually. How can I do this with GCODE?

RE: Brand new prusa mini: Z needs to adjust on every new print.

I am literally just trying that. My current Start G-code is

G90 ; use absolute coordinates
M83 ; extruder relative mode
G28 ; home all
G1 Z50 F720 ; park position
M104 S170 ; set extruder temp for bed leveling
M140 S[first_layer_bed_temperature] ; set bed temp
M109 R170 ; wait for bed leveling temp
M190 S[first_layer_bed_temperature] ; wait for bed temp
G4 S120; wait 2 mins
G28 ; home all without mesh bed level
G29 ; mesh bed leveling 
M104 S[first_layer_temperature] ; set extruder temp
G92 E0.0
G1 Y-2.0 X179 F2400
G1 Z3 F720
M109 S[first_layer_temperature] ; wait for extruder temp

; intro line
G1 X170 F1000
G1 Z0.2 F720
G1 X110.0 E8.0 F900
G1 X40.0 E10.0 F700
G92 E0.0

M221 S95 ; set flow

You have to create a new printer profile from the system one. I added lines to set the hotend pos before heating, and to wait for 2 minutes before doing mesh leveling.

RE: Brand new prusa mini: Z needs to adjust on every new print.

@bobcousins

Thanks, but I have a question.

You added this to the Start Gcode:

G28 ; home all
G1 Z50 F720 ; park position

So you park the Z at 50mm? Why? I think we have to set Z as low as possible to preheat the Minda with the heat of the bed?!

RE: Brand new prusa mini: Z needs to adjust on every new print.

It may be that the probe is affected more by heat from the hotend, I suspect it is, but I don't really know.

I get consistent results if I wait a few minutes after doing a print before starting the next one, so usually the hotend is somewhere above the heatbed. I'm not sure it is important exactly where the probe is compared it to being in the same place each time. However, that is something I will try to experiment with.

Please feel free to adjust things like the position, and the sleep time, and see what works best. I do think your Z-height is unusual, possibly there is an issue with your probe.

RE: Brand new prusa mini: Z needs to adjust on every new print.

Not got a Mini with the Minda but even on the Mk3 with the PINDA some of us use custom start gcode to position the pinda close to the bed in the middle and turn on the extruder and bed (160/75) to preheat the Pinda to a set temperature before doing mesh levelling to get a more consistent result.  The pinda isnt temp compensated but it does have an onboard thermistor so instead of waiting a set time we can just wait until the pinda reaches a set temp, in most cases 35 degrees.

On winter cold days that can take over 5 minutes to reach temp but at the moment is usually only a couple of minutes.

RE: Brand new prusa mini: Z needs to adjust on every new print.

Interestingly, I wasn't having this issue until my Minda failed and support sent me a new one. I went weeks without adjusting Z-height using the original Minda. Now I have to adjust it before every print.

RE: Brand new prusa mini: Z needs to adjust on every new print.

I have the same issue. Only thing that helps is preheat for 10min with printhead near bead so that the probe gets warm, but even then i have to recalibrate for other material with other temps or even if i left the window open.  I contacted the Support Chat because of it today.  There i was told that the Minda has a Thermistor build in like the Pinda Probe, but the Buddy Board FW dosn't support it yet. Dont know how it works if the Minda only has 3 wires, but maby new Firmware will fix it.

RE: Brand new prusa mini: Z needs to adjust on every new print.

I created the gcode below that you can use to warm up the Minda probe before starting a print on a cold MINI printer. Copy the text below and paste it into a new file. Be sure the file has ".gcode" as the suffix.

; Prusa MINI Minda probe warmup code
;
; There is a known issue where the initial z height is not correct if mesh bed leveling
; is performed with a cold Minda probe. There is no temperature correction in the Minda 
; probe on the Prusa MINI. Just warming the hot end isn't enough to get the Minda probe
; warmed up since it's not directly connected to the hot end. 
;
; Use this code to preheat the Minda probe before starting a print on a cold printer.
; The print head is moved close to the bed to let the bed heat help to heat up the 
; probe as well as allowing some reflected heat from the hot end. There is a delay
; that allows some time for the probe to heat up before the gcode ends.
;
; Written by Rick Miller 26 March 2020
; Preheat temperature extruder: 170°
; Preheat temperature bed: 60°
;
; 1: Set extruder and bed temps
; 2: Home the printer without performing a mesh leveling
; 3: Move to roughly the middle of the bed and z height slightly above the bed
; 4: Wait for extruder and bed temps to reach the set points
; 5: Pause for 2 minutes (arbitrary delay that you can change in the code if you wish)
; 6: Raise height and move the head closer to the zero position (front left)
;
; The move to the middle of the bed is to help surround the Minda probe with heat.
; The 2 minute pause was an arbitrary delay. If you want to change the length of the
; delay, look for the M0 command in the code below. Change the number of seconds to
; wait by changing the number following the 'S'.
;
; Note: You should be able to cancel the wait by pressing the encoder knob but
; that is not currently working on the MINI at this time on V4.1.1.
;
; These first few lines are common to all gcode generated for the MINI
G90 ; use absolute coordinates
M83 ; extruder relative mode
;
; Set temps before homing to give them a bit of a head start 
M104 S170 ; set extruder temp for bed leveling
M140 S60 ; set bed temp
;
; Home the axis without mesh leveling (W disables mesh leveling for this homing cycle)
G28 W ; home all without mesh bed level
;
; Move to roughly the middle of the bed and lower the z to 1.5mm above the bed
G1 X100 Y100 F4000
G1 Z1.5 F50
;
; Wait for the extruder and bed temps to reach the set points
M109 R170 ; wait for extruder temp
M190 S60 ; wait for bed temp
;
; Delay to allow the Minda to warm up
M117 Allow Minda probe to warm up
M0 S120 
;
; Move the head closer to the zero point on the bed and raise the z a bit
G1 Z3 F50
G1 Z5 F100
G1 X50 Y50 F4000
;
; Housekeeping
G4 ; Wait for movements to complete
M84 ; Disable motors
;
; Note that these estimates will depend of a few factors like where the print head was
; and what the temps were at when we started.
; estimated printing time (normal mode) = 2m 30s
; estimated printing time (silent mode) = 2m 30s

RE: Brand new prusa mini: Z needs to adjust on every new print.

I contacted the support because of this issue and linked them to this thread. They told me the MINDA has no Thermistor and they think the Sensorcable is broken and send me a new one. But I still think its a temperature problem. I will try.

„The MINDA sensor doesn't have  build in thermistor. According to the information which you provided me, it seems like the cable from MINDA is partially broken. We will send you a replacement one as soon as possible.“

RE: Brand new prusa mini: Z needs to adjust on every new print.

Well, there could be more than one problem. The MINDA cable is a known source of issues, so worth replacing. If you haven't already I would look at cable relief mods.

RE: Brand new prusa mini: Z needs to adjust on every new print.

I'm having the same problem. Support sent me a new MINDA probe and there was definitely an improvement after the swap but not totally fixed.

I do believe the issue is at least somewhat heat related as it seems to mostly happen when the probe is cold. I have my start gcode to home first thing so the probe is close to the bed as it heats up which again helps but isn't a total fix. 

I don't know why they insist on using these inductive probes, must be a cost thing. I put a BLTouch on my Ender 3 and it works perfectly every time. The only time I ever have to touch the Z offset is when I change nozzles. They make a lot more sense with swappable beds as well since you don't have to adjust after a bed swap.

RE: Brand new prusa mini: Z needs to adjust on every new print.

I guess cost, but also gives Prusa some special source which they think might deter clone builders, although the clone builders are probably located next door to the company making the Prusa probes and can get them quite easily. You can already buy all the Mini parts on Aliexpress for example, but you can't buy spare probes in the Prusa shop.

RE: Brand new prusa mini: Z needs to adjust on every new print.

i tried all different preheating methods, but i still have differences up to 0.5mm. Thats totally unusable. The only way i get good prints is with an extra calibration print in the same file as the actuall print and live tune first layer before every print. There has to be something wrong other than only the heating, because i preheat the printer straight for 15min befor every print atm... But it allways goes in only one direction on the same day that the nozzle is to high. Problem is, at the next day, with the nozzel moved 0.5mm down it scatches my sheet if i dont reset the z-offset and start fresh...

Not sure about the quality/usabiliy of the Mini ath this point becaus untill now i acumulated the Z Probe problem, had the problem with the hotend fitted not high enought and therefore way to much delay in the filament extrusion, the printer was delivered with a cracked electronic casing and last but not least the x-y ortogonality was rly bad, the axis had +-1° error (not to speak of the x/y length error of ca 0,5%) which lead to unusable prints for parts other than decorativ. But to some point thats all calibratable/fixable, hotend works better after compelete rebuild (bot not as god as the mk3, still need to much linear advance), casing could be fixed with super glue,  x/y error is calibratable and the angle error is mostly adjustable and comes from tolerance in the screws bolting the z axis together (and some ange instabiltry because of the asymetrical design but that can be fixed with not moving the printer after calibrating at all).

But the one problem i cant get arround is the Z Probe. With the Z-Probe problem 3 out of 4 prints fail. But since i can't belive that Prusa ships alls Minis with such a problem without noticing maby i should try to get in touch wich support again, it has to be related to a bad M.I.N.D.A. Probe in some way. Maby its fixable with an exchange. Even if i wish i ordered the Mk3s in the first place at this point, just to get reproducible prints. But maby my standards are to high, and it was illusional to get the same performance of the Mk3s just in smaller for a lower price, who knows.  If thats what you get maby it should be comunicated more clear.

So long and sorry for the kind of rant i still love the concept of a cheaper more beginner oriented printer and would love if it, if it would just work out a little better.

RE: Brand new prusa mini: Z needs to adjust on every new print.

Posted by: @julian_bauknecht

i tried all different preheating methods, but i still have differences up to 0.5mm. Thats totally unusable. The only way i get good prints is with an extra calibration print in the same file as the actuall print and live tune first layer before every print. There has to be something wrong other than only the heating, because i preheat the printer straight for 15min befor every print atm... But it allways goes in only one direction on the same day that the nozzle is to high. Problem is, at the next day, with the nozzel moved 0.5mm down it scatches my sheet if i dont reset the z-offset and start fresh...

Not sure about the quality/usabiliy of the Mini ath this point becaus untill now i acumulated the Z Probe problem, had the problem with the hotend fitted not high enought and therefore way to much delay in the filament extrusion, the printer was delivered with a cracked electronic casing and last but not least the x-y ortogonality was rly bad, the axis had +-1° error (not to speak of the x/y length error of ca 0,5%) which lead to unusable prints for parts other than decorativ. But to some point thats all calibratable/fixable, hotend works better after compelete rebuild (bot not as god as the mk3, still need to much linear advance), casing could be fixed with super glue,  x/y error is calibratable and the angle error is mostly adjustable and comes from tolerance in the screws bolting the z axis together (and some ange instabiltry because of the asymetrical design but that can be fixed with not moving the printer after calibrating at all).

But the one problem i cant get arround is the Z Probe. With the Z-Probe problem 3 out of 4 prints fail. But since i can't belive that Prusa ships alls Minis with such a problem without noticing maby i should try to get in touch wich support again, it has to be related to a bad M.I.N.D.A. Probe in some way. Maby its fixable with an exchange. Even if i wish i ordered the Mk3s in the first place at this point, just to get reproducible prints. But maby my standards are to high, and it was illusional to get the same performance of the Mk3s just in smaller for a lower price, who knows.  If thats what you get maby it should be comunicated more clear.

So long and sorry for the kind of rant i still love the concept of a cheaper more beginner oriented printer and would love if it, if it would just work out a little better.

Good luck with support, every time I've talk to them they act amazed that I'm having this issue but no solutions. The last guy I talked to disconnected on me and I haven't felt like dealing with them since.

RE: Brand new prusa mini: Z needs to adjust on every new print.

I contaced support, was rly quick and helpfull this time, they send me a replacement Probe. Will report if that fixes the Problem.

RE: Brand new prusa mini: Z needs to adjust on every new print.

I have this same problem. I got my printer about a week ago. My z height calibration just degenerates over every few prints.

RE: Brand new prusa mini: Z needs to adjust on every new print.

I recived and installed the replacement Probe. Now the error is way better. Before the Error was around 0,5mm diviation, what lead to unusable prints and a scratched bed. With the replacement Probe however its still not perfect, without preheating the Error is around 0,1mm and with preheating its aprox 0,05mm. That dosnt lead to perfect first layers, but usable ones, that stick every time. Im happy that i can use the printer now, but i hope that it will be possible to use the temeratur corrected PINDA probe instead of the cheap MINDA probe in the future, since the Buddy board already has the connector for the 4Pin PINDA with the fourtht pin that is acutally unused with the MINDA labeld "Thermistor".

RE: Brand new prusa mini: Z needs to adjust on every new print.

My take on this problem: on my first Mini the Minda wasn´t fixed straight and really tight (old design). After I really tightend it properly everything was fine.

Could it be possible that the heatblock is softening the Minda connection and thereby change the Z height?

RE: Brand new prusa mini: Z needs to adjust on every new print.

I have the same problem. In the morning, the probe is good with and offset of 1.110 mm. In the evening, is it 1.060 mm for the same result.