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Homing and G0 X0 Y0 Z0

Posted by Leslieval 
Homing and G0 X0 Y0 Z0
May 01, 2021 05:08AM
Hello, I am sure someone can help me with what is probbly a very simple solution to my probably very basic question? My printer is using Marlin 2.0. I have set Configuration H parameters as follows
// Travel limits (mm) after homing, corresponding to endstop positions.
#define X_MIN_POS -15
#define Y_MIN_POS -10
#define Z_MIN_POS 0
#define Z_MAX_POS 240
When I Issue a Home command either from the LCD on the machine or via G28 the print head goes to X -15, Y -10 and Z -0.05 (this Z height is what I find strange). As I manually level my bed by using Home and then adjust bed levels as required to get nozzle clearance I have now realised the nozzle is already starting at Z -0.05. Shouldnt it be at Z 0? and if so why is it at Z -0.05? I use Cura to slice my model and assume it thinks the starting point for the print is X0, Y0, Z0. The print head certainly starts in the right location and if I send a G0 X0 Y0 Z0 the print head goes to the front left hand corner as required and the LCD shows X0 Y0 Z0 but obviously I have levelled my bed with Z -0.05 so I am already slightly incorrect in my Nozzle gap. Not much I know but.....?
I hope someone can help me understand what is going on, what I should be expecting and what I can do about it. I am particularly perplexed as to why the Z -0.05 is being used and where it is coming from.
I hope I have explained my problem and maybe its not worth worrying about but it does seem to be contrary to what i should be doing and expect - or am I just totally misinterpreting the whole thing?
Regards and thank you in advance
Re: Homing and G0 X0 Y0 Z0
May 01, 2021 07:41AM
? some baby stepping offset persisting?
Re: Homing and G0 X0 Y0 Z0
May 02, 2021 12:56AM
Thank you for responding mechabits. I am not sure what you mean by baby stepping offset persisting? I have turned the printer on and off several times so i assume that would reset Marlin for any tuneing changes i might make when printing. Is there something i should be looking at?
Re: Homing and G0 X0 Y0 Z0
May 03, 2021 01:55PM
How are you homing Z? Are you using a probe or an end stop? If you're using a probe the NOZZLE_TO_PROBE offset is subtracted from 0 to determine the location of Z after homing. Use M851 to see what your probe offsets are and make sure that the Z probe is correct (in the majority of cases it should be negative).
You should also look at MANUAL_Z_HOME_POS.
You might want to post your complete configuration files so we can look for anything else that may be affecting things, and it never hurts to reinitialize EEPROM with M502 followed by M500 to ensure that the values in your firmware are actually the values being used.
Re: Homing and G0 X0 Y0 Z0
May 05, 2021 10:53PM
Hello and thank you for your reply. My apologies for my delayed response. I have just recently had my Covid shot and had a mild reaction to it but no complaints. I am now back in my office and on restarting my printer and homing it I can see it is now showing z = 0 so the -0.05 has now magically disappeared:-) I had restarted my printer several times before my previous post so unsure how it was picking up the Z setting I was seeing but as it is now showing as expected I will just monitor it and see if it comes again.
When printing I sometimes use the "Tune" option for Z available in Marlin and could have set that to -0.05 during first layer printing but I would have thought that would be lost after I restarted the printer but maybe not??

Anyway thank you agin for your help it is much appreciated. I have finally purchased a levelling probe (3D Touch) and will attempt to get that working in the near future.
Best regards
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