Z offset question
I have been printing now for a few months, i had finally gotten the Z offset corrected so the first layer went down as i thought it should. The offset was set to .24.
I installed a new nozzle (much sharper point) that sits lower than the original, so i re-calibrated the zprobe, had to move the sensor down.
Using the same process as before, with a clean nozzle, i put the nozzle on the bed, moved the sensor down (i put a quarter on the bed and set the sensor on top of the quarter, then tightened it into place).
I would have thought this would have been a close place to start Then i set out to re-calibrate the offset.
Using an aluminum reference block (39.95 mm)
reset the offset in the firmware to 0 (to make life easier)
I sent a G30 P0, the hot end moved to x100, y100, z19.843
i heated the bed and hot end and sent an M114 (that gave me 20)
moved the hot end so the block just slide under the hot end and sent an M114 (gave me 39.84)
using the formula (ZHNew = Zhold-Z0-znew+zold_ref) or (0-19.843-39.84_20_39.95) the offset should have been .267...
When I set this in the firmware and tried to start a print, the first layer was so tight, nothing came out of the hot end.
Just for testing, i changed the offset value several times.
After several attempts, i ended up using a negative number (had to try something different)..
Using -0.3 i was finally able to get the first layer to print.
Can anyone tell me where i went wrong with my calculations? I thought that the measurements for the offset should be positive if using a probe instead of a force feedback switch?
Am i backwards here?
I installed a new nozzle (much sharper point) that sits lower than the original, so i re-calibrated the zprobe, had to move the sensor down.
Using the same process as before, with a clean nozzle, i put the nozzle on the bed, moved the sensor down (i put a quarter on the bed and set the sensor on top of the quarter, then tightened it into place).
I would have thought this would have been a close place to start Then i set out to re-calibrate the offset.
Using an aluminum reference block (39.95 mm)
reset the offset in the firmware to 0 (to make life easier)
I sent a G30 P0, the hot end moved to x100, y100, z19.843
i heated the bed and hot end and sent an M114 (that gave me 20)
moved the hot end so the block just slide under the hot end and sent an M114 (gave me 39.84)
using the formula (ZHNew = Zhold-Z0-znew+zold_ref) or (0-19.843-39.84_20_39.95) the offset should have been .267...
When I set this in the firmware and tried to start a print, the first layer was so tight, nothing came out of the hot end.
Just for testing, i changed the offset value several times.
After several attempts, i ended up using a negative number (had to try something different)..
Using -0.3 i was finally able to get the first layer to print.
Can anyone tell me where i went wrong with my calculations? I thought that the measurements for the offset should be positive if using a probe instead of a force feedback switch?
Am i backwards here?
Comments
Especially if you have z max homing you need to recalibrate height using G32 S2. Just changing z probe height does not correct wrong z length here.
After setting this to a negative number, i did rerun a g32 s2 and then a g33.
After this i was able to get the first layer to print.
After working with this for a few days, i found that the only way i could get even close to a good first layer was to enter a negative offset.
I re-loaded the firmware (version 1.0.2) and still was unable to get it to work without a negative value.
I uploaded the newest version of firmware (1.0.3), tried to re-calibrate the offset. I tried 4 different times and got 3 different values for the offset (.53, .83 and .32), i have been trying to calibrate in the same spot on the printer each time. The only thing that was different was the spot where i sent the initial G30 P0.
With the offset numbers i found, when i home everything, then move the z axis first, i hear it drag on the bed (so i am still too close).
now, for some reason, when i turn the printer on.. the first thing i do is home everything, what happened before was the Z axis would raise 10, then x would home, y would home, the printer would move to x100, y100 and then z would home.
Now, after upgrading the firmware, when i turn the printer on and home everything, Z homes where it is, then x homes, y homes and z homes again.
This is an issue if the z probe is not over the bed when i turn the printer on.
i tried also to go back to version 1.0.2 to see if the issue corrects, but it does not.
Also, after upgrading the firmware, using the same config file that the printer was running, the first time i tried to home everything, the Z axis started to go up and then everything stopped with an illegal out of bounds error, i changed the x offseet for the probe and the error stopped, i then put it back to where is was (since it was no longer even close to the actual offset), when i changed it back, the error did not come back.
i am completely lost here....
Any thoughts on this would be greatly appreciated. Do i need to replace the RAMPS board since this is somewhat inconsistent? Or do i need to do something different?
When probing make sure autolevel/distortion correction is enabled. What you do is correcting z probe height so that the reported position under current conditions would fix the block when setting z to block height so it just has no play. If the correction leads to different distances over different points you will get different probe heights. That is why correction must be enabled. Then error should be nearly identical at all points.
It does not depend on the ramps.
You might test relyability of the z probe. Go to one point and run multiple G30 to see if results change over tests. A small deviation is normal.
here is what i am doing..
I power up the printer and home everything
i get the ZHold number from the eeprom z probe height (1.2)
my reference block is 39.55 mm
I then move the head to x100, y100, z10, then i send a g30 p0 to get z0 (11.074)
i send an m114 to get zold (11)
then i adjust the head so the reference block just fits under and send an m114 (40.09)
then the math
znew= zhold -z0 -znew +zold +ref
1.2 -11.074 -40.09 +11 +39.55
this gives me .586
so i put .586 into the eeprom as the new z probe height, and home everything again
i raise the z to 10 then move x and y to 100,100 then i send a g1 z0 (which in theory "should" put the hot end right on the build plate right???
what i actually get is the hot end is off of the bed. if i then change the z probe height to 1.2 (just a guess, re home and move to z10, x100,y100 and send a g1 z0 the hot end goes to the build plate.
This put me back in the "I am going to guess at what the offset should really be..
What am i missing here..???
Thank you for all of the help and patience..
Does homing use the z probe? In that case you should be allowed to just measure block and change z height by difference measured block height vs. real block size.