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BL Touch Z Offset having not effect


gregorybarrett1983
(@gregorybarrett1983)
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I installed a BL touch on my Ender-3 Pro a couple of months ago and worked fine. Have not used the 3d printed much since so set it up again homed it and adjusted the Z offset to suit. I start the print off it auto homes, then goes across the all the bed to pick up the 9 points then purges down one side with a good squish. When it zips off to start the main print it seems to go up in the Z axis because the filament it not adhered to bed at all well. 

If I touch the Z axis lead screw I can feel it moving ever so slightly as it auto adjusts it self when purging, at the end it goes up then back down again to start the print but cannot tell if it has not gone down to the same level. I have re-flashed the (2019.11.13)Ender-3 Pro1.1.6BLTouchV3.1PowerLossContinueEnglish.hex without having any effect. When installing I following the Creality video

and added G29 before it homes in the machine setting in Cura.

The odd thing I noticed is when you perform the bed levelling than the Z offset value is already zero and all of the videos I have watched seems to have a value in there already which you add to the Z value when manually adjusting with a piece of paper. My Z offset needs to be -3.30mm which seems to be not far off the videos I have seen.

I have used the manual bed levelling screws to make sure the bed is as level as possible and the bed is not too warped. If I keep on adjusting the Z offset to silly numbers like -6.00mm it has not effect and does not ram into the bed. I fully understand how it should work but have not got a clue why the value is being ignored. Every time I make an adjustment I store the settings, but do not get any conformation if it has worked. I suppose it must be working as the values is still there after a reboot.

I am a novice 3d printer and not that interested in upgrading the firmware, I just wanted a simple to use plug and play 3d printer.


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kevin
(@kevin)
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@gregorybarrett1983 Hi, friend. First, you have to understand that maybe the Bltouch is not as much smart or intelligent as you think it is. Bltouch is just a subsidiary to make your bed leveling easier and more accurate to let the first layer of your print have better adhesion. You can get the confirmation by checking if the Z-offset number has changed. 


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gregorybarrett1983
(@gregorybarrett1983)
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I understand how it should work.  The zero offset is the difference between the end of the extruder and where the tip of the bl touch. The trouble is any adjustment does not seem to do much. Is they suppose to be a value already in the z offset after performing bed levelling or homing?  If so where does the number come from?


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Wurlitzerwilly
(@wurlitzerwilly)
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Joined: 5 months ago
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@gregorybarrett1983

The best way to get this right is to set the Z-offset to zero.

Home all axes, then move the Z axis (nozzle) to zero. Slide a piece of paper between the nozzle and bed and use the Z-offset to lower the nozzle until it just grips the paper. Now SAVE the Z-offset value.
Now you're in the right ball-park - manually level the bed in all 4 corners and center - several times to iron out any interaction between the adjusters.
Home all axes again and set the Z axis to zero. Re-check Z-offset with paper and adjust if necessary. A value of around 0.3mm is typical. SAVE the Z-offset value again, if you changed it.
Now probe a mesh with the BLTouch and SAVE the values.
You can now use G29 after G28 to probe a mesh at the start of each print or you can use the stored mesh using M420 S  Don't use both!
If you are saving values to the SD card, you MUST have the same SD card in place for every print or the values will not be picked up. If you're saving to Eeprom, you're good to go.


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gbartley
(@gbartley)
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I am having a similar thing happening with my ender 3 v2. I also just recently install a BLTouch and now I have no control to the z axis at all. Has anyone else had this issue and if so what was the fix?

 

Thanks

Gerald


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Dayack
(@dayack)
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I have seen this twice with my E3 since the BLtouch was installed.

My Z offset is set at 2.72 and mostly works fine.

 

The first time I had the issue, the nozzle moved down, and scrapped across the bed, with barely any material being left.

The second time, The nozzle moved up, and nothing would adhere after the purge line.

 

The first time I modified the z offset to 2.5 with no change, and the second time I modified it to 2.85 with no change.

 

After pulling everything apart and cleaning the system, tightening everything up, load eprom to rest defaults, and re-adding the original offset again, then the system seems to start working properly again.

 

Not sure what the problem is, but it seems to mostly be working properly each time.


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kevin
(@kevin)
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Joined: 3 months ago
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@dayack Do not know why the nozzle hit the bed heavily just now when auto home. But when I re-auto home, everything is fine. Can't explain why it made a mistake last time.


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