Cannot adjust z offset on a8

I have been banging my head against the wall for 3 days straight on this one. Any suggestions greatly appreciated.

Printer is a stock Anet A8 with a fresh copy of marlin 1.1.9 installed. Installation went without a hitch. The config.h file is the stock file that comes with marlin, with the only significant change being the offsets for the capacitive sensor (x=0, y=52, z=5). The z offset doesn't seem to make any difference. I can increase it or decrease it and after homing the nozzle always winds up in the same place (about 4 mm above the bed). The z offset on the display reads the same as whatever I set in the config.h file. I can change it on the display, but again the nozzle always winds up about 4 mm above the bed no matter what offset I chose!

Just for fun I tried a test print of a small dot. It printed perfectly and in the center of the bed but 4 mm above the bed!

I must have accidentally set something (or not set something) in the config file to make the z offset fixed but darned if I can figure out what !

Thanks for any help you can offer.

Upload your configuration.h file to a file share like google drive post a link here will that a look.
Have helped others get there 3D Printer working on Marlin 1.1.9 However I suggest the Marlin 1.1.9BF ("bugfix version") as more stable.

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Computer Programmer / Electronics Technician

Thanks for the offer of help .... I'm losing sleep over this !!

[drive.google.com]

BTW I think all my changes from the standard "examples" file are marked so ------------------------*---------------------
A search for -*- should yield every location I've made a change.

Edited 1 time(s). Last edit at 04/18/2019 08:40PM by schuh8.

I see you have enabled Bi-Linear bed leveling. Though you have no Probe boundaries setup.

  //#define LEFT_PROBE_BED_POSITION MIN_PROBE_EDGE
  //#define RIGHT_PROBE_BED_POSITION (X_BED_SIZE - MIN_PROBE_EDGE)
  //#define FRONT_PROBE_BED_POSITION MIN_PROBE_EDGE
  //#define BACK_PROBE_BED_POSITION (Y_BED_SIZE - MIN_PROBE_EDGE)

Enable Restore leveling After G28

//#define RESTORE_LEVELING_AFTER_G28

After flashing Send
M502 ; Factory Reset
M500 ; Store Settings

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Computer Programmer / Electronics Technician

I followed your suggestions on setting the probe bed positions and now the auto bed leveling works perfectly. Thank you ... first time I've been able to get that working.

Unfortunately the original problem still exists, i.e. the extruder cannot be adjusted any closer than about 4mm to the bed. Printing in mid air is not the best .

Your configuration looks OK, except that Z_PROBE_OFFSET_FROM_EXTRUDER is 0 - that means that the printer thinks that Z=0 is wherever the z-probe triggers when homing. So out of the box (no M851 command) you would expect the nozzle to be a distance above the bed.
Try the following commands:

M851 Z0
G28
M211 S0

This will home the printer and disable software endstops so you can move the head down. At this point, the display should show Z=0
Use the "move axis" command to move the Z axis until the nozzle is close to the bed (I use a piece of paper and stop moving the axis as soon as I feel any friction when moving the paper).
At this point, the display should show a negative Z. Save this value, and use

M851 Znew_Z_offset

to set the offset . Make sure that you use the negative value! For example, on my AM8 with an inductive sensor I use

M851 Z-1.65

Now try the G28 again and see what happens.

Edited 1 time(s). Last edit at 04/19/2019 07:30PM by MMcLure.

MMcLure

I have followed your suggestions with some success!!! Been a long day and I will tear into it again tomorrow. But there's hope now !
More experimenting and I will report back, probably tomorrow. Thanks for taking the time to help !!

Once you've figured out the right Z offset, make sure you set it as your new Z_PROBE_OFFSET_FROM_EXTRUDER (and do the M502/M500/M501 dance) so you don't need to worry about it again.

Sorry this is so late, but I've been experimenting.

Clif's comments got my bed leveling working and MMclure's comments finally enabled me to set my z offset. I was also able to enable an option to turn on/off software endstops on the A8 screen. Most helpful as I usually print from a SD card.

All by way of saying thanks, y'alls help was invaluable !!