Nozzle digging into plate - no calibration errors
Hello! We had to detach the hot end this week in order to remove a strand of filament that became wedged in the barrel (throat?) of the hot end. In doing so, now all of a sudden our z height is off and the nozzle digs into the plate. However, when we conduct the calibrations (Z, XYZ, self test) we receive no error messages. Even when we start a print, it will dig into the plate when the printer runs through its 9 checkpoints without an error message, then will start the print job, still digging into the plate. We assume that it has to be something with the PINDA probe but are struggling to troubleshoot. The probe seems to light up as normal (red when sitting, goes off when something metal touches it). We hadn't remove the probe or even touched it when fixing the previous filament issue, other than to scoot the wire out of the way for the front fan's wire to come out of the guide.
We should also mention that the nozzle is pushing into the plate at different depths based on where it is on the plate. When you face the front of the printer, the right sides (and back middle) are digging in harder. We are hoping for a solution so that we can continue printing our students' final projects! Thank you in advance for your suggestions. (below is the extruder at the home position. The nozzle is pressed into the plate and the probe is just a hair to close for a dime to fit comfortably beneath it.
RE: Nozzle digging into plate - no calibration errors
Verify the PINDA is changing state at the controller - dig through the LCD menus to the PINDA status, and use a screwdriver close to the PINDA tip, the LCD should see a state change, and the PINDA LED should turn off and on at the same time.
If the PINDA is working (showing a change on the LCD), try lowering it a millimeter closer to the bed.
RE: Nozzle digging into plate - no calibration errors
Have you reset the "Live Z" calibration after putting the printer together? Everytime you disassemble the extruder, you should go through the XYZ calibration and the First Layer calibration, but before goint to First Layer it's good to check that Live Z is at 0 or some other conservative value.
RE: Nozzle digging into plate - no calibration errors
@tim-m30, we can't find the PINDA status anywhere in our LCD menu. (For reference, we have the i3 MK2, Firmware version 3.1.0, RAMBo13a) We'll do some Google searching to see if we're just somehow overlooking it. We can't imagine the status isn't in the menu...
@vojtech-p6 Our Live Z is at 0. We just tried the XYZ calibration again with the same results. When we try the First Layer calibration it gets through the first 2 checkpoints, digging into the plate. The 3rd (front right) pushes in quite a bit more, so the printer stops and gives "bed leveling ... check the nozzle for debris ... waiting for reset" error and stops.
RE: Nozzle digging into plate - no calibration errors
PINDA status is in Menu->Support->Sensors and it should match the status of the red light on the probe.
RE: Nozzle digging into plate - no calibration errors
Regarding your sentence "The probe seems to light up as normal (red when sitting, goes off when something metal touches it)" - that's indeed the correct behavior, however 'touches it' isn't precise. It should turn off before the nozzle hits the bed. If the light only goes out when the nozzle touches the bed, then the sensor is too high in the mount and needs to be lowered.
RE: Nozzle digging into plate - no calibration errors
@vojtech-p6 Thank you for the additional guidance. There isn't a "Sensors" option under Support, or in any other part of the menus. So we're still stuck on that end. However we followed your suggestion of lowering the sensor until the light goes out and have discovered that only when the sensor is lowered to the point of physically PRESSING onto the plate, does the red light finally shut off. Huh! So what do you suppose this indicates? Something with the sensor's wiring or the build plate itself perhaps?
RE: Nozzle digging into plate - no calibration errors
@kentstatesms I'm too used to the Mk3, I suppose the 3.1 firmware has a different menu structure. In any case, the fact that the sensor only reacts when touching the bed is the source of the problem. It is supposed to have a couple milimeters of detection range. You may need a new probe.
But then again I might not know the Mk2 well enough: What material is the bed made of? Does it have a steel sheet on top? The PINDA probe is inductive and detects metal - unless there is enough of metal underneath, it will not detect it.
RE: Nozzle digging into plate - no calibration errors
On a MK3 I believe it's under Support/Extruder Status. A MK2 may not have it. If not, then all you have is the LED, or if you are electronically inclined a multimeter at the Einsy end... but that won't tell you if the probe is being read properly by the CPU. Only that the signal is getting there.
The PINDA only detects metal in the heat bed - if it is over an area without embedded metal it will not trigger. Contact is NOT needed, nor desired. The PINDA should be about 1 to 1.5 mm higher than the nozzle. The assembly guide recommends using one of the included cable ties as a feeler gauge (about 0.045" or 1.15 mm). Use a piece of paper as protection, ensure the nozzle is very clean (no filament nipple) lower the nozzle to the bed, then adjust PINDA so the cable tie can barely slide under. And tighten.
Then, during XYZ cal, the printer does an XY home, and places the PINDA over a spot in the bed where there is metal, and begins slowing lowering Z until it "finds' metal. It then moves on to find the center of the four metal inserts that serve as X and Y calibration points. This adjusts X and Y step multipliers to accommodate for belt stretch, gear oddities, etc.
RE: Nozzle digging into plate - no calibration errors
I know you guys are trying to help but man this is getting dangerous. There are differences between the MK2/S and the MK3/S, not least of which is the sensitivity and type of the PINDA.
While the MK3 Pinda has a 2mm range, the MK2/S range is ONLY 1mm. Before starting the xyz calibration the MK2/S PINDA needs to be set approximately 0.7mm above the nozzle. The assembly manual recommends lowering z till the nozzle just contacts the bed and adjusting the PINDA so the main part of a standard cable tie will just slide under it. Tighten up on the retaining screw and raise z to start calibration.
Bill
Tagaytay City, Philippines
Founder member of Philippines Prusa Printer Owners FB Group
Sponsor Pillars of God Academy in Bacoor
RE: Nozzle digging into plate - no calibration errors
Bill - the cable tie approach is the same for a MK2 and a Mk3 ... same 1,15 mm delta (measured from a cable tie). And from what I've been able to glean around the web and various guides and manuals they both have a 2mm sense distance. The real difference is the MK3 has a thermistor (4 wire), the MK2 does not (3 wire).
Since I am not a Prusa employee, I can't confirm/warrant all these details, but I am reasonably confident my instructions above will not damage anything unless something on the printer is already broken; or the person doing the adjust isn't following them.