Nozzle touch auto bed leveling

I saw some printer on ali which use nozzle to touch heated bed in order to do autoleveling so I hew few questions

How safe is this moving speed while touching bed is very slow ?
Is this feature implemented in Marlin, can I install newest firmware and do same autoleveling in genuine marlin ?

You need some kind of sensor to sense the touch. Various kinds have been used; a microswitch, electrical, piezo-electric, load-cell. Marlin supports any of these... they just provide a digital on/off input to the controller.

I have a cheap AliExpress printer which came with the microswitch. The nozzle has to move (.5 mm or so?) to activate the switch. It's sprung to return it to the same place when the pressure is released when the nozzle is lifted. So there's a small Z distance between the "normal" and "touching" positions of the nozzle. On my printer, the spring wasn't strong enough, and the hinge mechanism also allowed some lateral movement. All of that led to a lack of repeatability in positioning the nozzle. I really think that this is more trouble than its worth, and I fairly quickly threw out the whole auto-levelling thing and just manually level the bed and set the Z=0 height.

Electrical relies on measuring the resistance between nozzle and a metal bed... when it's zero, the nozzle is touching. Obviously you can't use this if you print onto glass or tape. I don't know how well this works, but you can imagine what happens if there's some filament stuck between nozzle and bed. I don't think many people use it.

The other 2 are (relatively) expensive and newly developed or even experimental; I'd be surprised if you got them on an AliExpress printer.

Edited 1 time(s). Last edit at 09/24/2017 07:13PM by frankvdh.

I dont see why sprint and switch and needed Im thinking just using nozzle and aluminum bed as switch, the nozzle is touching the bed so there is your perfect switch its at zero height its not needed anything just implement it in code and let users decide will they gone use it. But tnx for quick replay cheers

This method relies on measuring the resistance between nozzle and a metal bed... when it's zero, the nozzle is touching. If your printer has a metal structure, the nozzle may already be electrically connected to the bed, so it will always read zero.

Obviously you can't use this if you print onto glass or tape, which is exactly what most people do.I don't know of any people printing directly onto the aluminium bed.

Unless you use some electronics (it could just be a couple of resistors, or maybe a transistor) at the controller board, you'll need to run 5V (or 3.3V, depending on the type of controller board) to the nozzle. If a short circuit occurs from your 12V heater supply to 5V sensor input, you will probably destroy that input on the controller, and may destroy the entire controller board.

If there's some filament stuck on the nozzle then the nozzle (especially if it is cold) will never touch the bed and trying to set the height or auto-level will drive the hotend into the bed, probably damaging the printer.

Personally, I think that this is worse than nothing; at least if there's no sensor, you know to manually set the nozzle height, and NOT to use the home or auto-level commands. And there's nothing to damage your printer.

heating the hotend and a automated wipe system to clean the nozzle tip is required...

Quote
frankvdh
This method relies on measuring the resistance between nozzle and a metal bed... when it's zero, the nozzle is touching. If your printer has a metal structure, the nozzle may already be electrically connected to the bed, so it will always read zero.

Thank you for nice explanation my heat bed is separated from printer frame they do not have any conductivity between them

Quote
frankvdh
Obviously you can't use this if you print onto glass or tape, which is exactly what most people do.I don't know of any people printing directly onto the aluminium bed.

Yes I cant I put some type and adjust baby stepping by 0.05-0.1

Quote
frankvdh
Unless you use some electronics (it could just be a couple of resistors, or maybe a transistor) at the controller board, you'll need to run 5V (or 3.3V, depending on the type of controller board) to the nozzle. If a short circuit occurs from your 12V heater supply to 5V sensor input, you will probably destroy that input on the controller, and may destroy the entire controller board.

If there's some filament stuck on the nozzle then the nozzle (especially if it is cold) will never touch the bed and trying to set the height or auto-level will drive the hotend into the bed, probably damaging the printer.

Personally, I think that this is worse than nothing; at least if there's no sensor, you know to manually set the nozzle height, and NOT to use the home or auto-level commands. And there's nothing to damage your printer.

Thank you for nice text I will consider these in future