This sounds like a proximity sensor fault.KenW wrote: Sat Nov 11, 2023 12:44 am Somebody on one of the Facebook Tina2 groups has posted a video of their Tina2 printing all the layers on a slant.
When I requested further information, it turned out the bed levelling calibration only did the first pass (but it presumably had always done that so they didn’t know it was incomplete).
I’ve asked for a video to see exactly what happens during a z offset calibration, but I’m still waiting.
Meanwhile, any comments?
The proximity sensor is the rod with the rubber tip mounted to the right of the nozzle (see Item 1 in the photos above, noting that the tip is blue in the photos but the original part is orange). The sensor uses a magnetic field to detect the steel plate under the removable magnetic print surface without contacting it, and it is used to calibrate the z (vertical) position of the first print layer. There is a LED on the top end of the sensor (where the cable comes out) which lights when there is steel (or similar) within the detection range of the sensor, and this is coincident with the signal sent to the controller.
The sensor itself can be tested (if the printer is powered up) by bringing something made of steel close to the tip and watching for the LED to come on. (This, and mechanical adjustment, is easier if the guard is removed.) Note that stainless steel (eg cutlery) is not suitable.
The software running in the controller also uses the sensor to take a reading of the bed in three places before every print so that it can automatically adjust the print process for the bed being off-horizontal ("bed levelling" – it doesn't actually level the print plate, it compensates for the plate not being level). It does this by adjusting the z of the nozzle within a layer (when you would expect z to remain constant) according to the x and y of the nozzle and the compensation calculation derived from the bed levelling operation.
I've had two different sensor faults with different consequences, both the result of a broken wire which makes or breaks contact as the cable flexes(the differences being according to which wire out of the three in the sensor cable is intermittent). I've also had an intermittent cable to the heater (see posts above)!
- If the +12V wire is broken, the controller believes the sensor has been triggered even when it isn't. The LED will be off.
- If the 0V wire is broken, the controller believes the sensor has not been triggered even when it is in proximity of the bed. The LED will be off.
- If the signal wire is broken, the controller believes the sensor has not been triggered even when it is in proximity of the bed. The LED will be on or off reflecting the true sense state, but this information does not reach the controller.
The following assumes the proximity sensor is fitted at the correct height in the hot end assembly, ie it detects the bed before the nozzle makes contact with the print surface, but it is not lower than the nozzle (preferably a little higher – the lower it is, the more likely it is to foul the print). The clamping screws used to fix the sensor in position are of poor quality with rough tips, so they bite on the threaded barrel of the sensor and force it into one notch or another – I found that filing the screw tips flat made exact adjustment much easier.
During Bed Levelling
The bed levelling operation can be performed from the menus, but it is invoked automatically when commencing any print, and as a preliminary to Z offset calibration. The correct sequence of operations is:
- The nozzle positions front left, and lowers quickly at first, then slowly for the last 10mm or so until it triggers the proximity sensor, then lifts about 10mm.
- The nozzle positions front right (not so far to the right – the sensor has to remain over the plate), then lowers slowly until it triggers the sensor, then lifts about 10mm.
- The nozzle positions back right, then lowers slowly until it triggers the sensor, then lifts about 10mm.
- The nozzle then remains in this position (menu operation), or remains in this position while it heats up before commencing the print (print operation).
During Z Offset Calibration
Bed levelling is performed automatically as a preliminary to Z offset calibration. Consequently is it very unlikely that the process will get as far as actually calibrating the Z offset if the proximity sensor is faulty.
However, for information: the Z Offset menu operation lowers the nozzle until the sensor detects the bed (this is "zero" point). The exact offset between the sensor trigger height and the position of the nozzle tip can then be dialled out using the rotary knob, in hundredths of a millimetre. The recommended offset is to use a slip of ordinary copy paper as a feeler gauge, and adjust the knob so that the paper is not quite pinched between the nozzle and the bed – it can be moved, but with some resistance. It's easiest if you position the paper under the nozzle before you start the Z Offset operation.
The print nozzle needs to be clean when you do this. If necessary, the nozzle can be cleaned by performing a retract filament operation, and wiping the nozzle with a wad of kitchen paper while it's hot (be careful!).
If (due to a fault) the controller thinks the sensor has triggered when it has not, the Z Offset will leave the nozzle in the air, nowhere near the bed. If the controller thinks the sensor has not triggered, the nozzle will hit the bed and the z motor will make a graunching sound because it is being driven but can't move (I don't know whether any self-protection kicks in – be prepared to pull out the power plug).
Note that if the fault is intermittent, it might not show up during Z Offset.
This video below shows the correct functioning of the Tina2 during a print, which always commences with a bed levelling operation. Any deviation is indicative of a fault.
Post 1 in this thread provides details of disassembly and replacement (viewtopic.php?t=560)
