https://www.youtube.com/watch?v=51VsyV4i7OM

Is this the first time we've seen using the head itself to set the bed height? It does look like I could still knock it out of line trying to free a stubborn part. I guess that's why it apparently does it every print, which would be time consuming.

Hopefully the wing/jam nuts on the leveling screws I mentioned earlier will offer a solution to Operator Induced Unlevel Print Bed Syndrome. Be sure to ask your doctor is wingnuts are right for you.

The bed is supported on springs which are around smooth tubes rather than screws.  It's a little hard to see what is going on with the levers, but there is a gap between the lever section and the mounting section below it.  When the end of the lever pushes outward, it bends and grips the tube which is supporting the bed.  The bottom of the gear is a cam which is shaped to press each lever in turn.

When beginning leveling, all the levers are released.  The head moves to the first of 3 leveling points and moves to a specific z height, low enough to push the bed down against the spring.  While the nozzle holds the bed down, the motor turns the gear, moving the cam into position to press the first lever and grip the tube, holding that point of the bed in place.  The nozzle rises and repeats the process at each of the other points.  After printing, the cam rotates to a point where all of the levers are released again.

The inventor of this process did it on a Rep2, using the gcode controlled fan pin to drive the motor.  Plenty of controllers have enough pins to run this without using the fan.  I'm not sure what the limit switch is for, most likely there are bumps on the cam to trigger it at each position the motor needs to stop.

I'm convinced that rough handling does indeed take the bed out of level. It's to be expected too, since the leveling screws have no locks.

I have ordered 4MM x 50MM flat head socket screws and wing nuts from McMaster. I will replace the stock leveling screws with these. Once I have the bed nicely tweaked, I will tighten the wingnuts on the lower end of the screws and see if that doesn't keep the bed level even during enthusiastic part removal.

If I'd thought it through, I'd have stuck the Print Tite onto a mirror for removal/rough handling.

Anyway, I'm hopeful the wing nuts (jam nuts) will keep the bed level more or less permanently.

^ this, without a doubt.

on the SD's, I hardly ever have to tinker with bed level anymore (unless I have to get rough with it removing larger parts, lol). Getting them set up well to start with - a nice, flat, glass surface, and good Z height adjustments - go a long ways towards eliminating the need to fuss with it.

The induction sensor is triggered by the proximity to the aluminum bed.  Whenever you have something else on top the print bed, your print head is further away from the actual metal, and so is the sensor, which obviously can't be set any lower than the print nozzle. 

The sensors used for bed leveling are usually low cost tube type inductors with a short sensing distance (4-6mm).  So if you have something on top of your printbed, like thick glass, mirrors, PEI, etc, the distance between the sensor and the metal increases and as it gets near the maximum of the range, the sensor becomes more erratic which sometimes leads to a head crash into the print surface. 

At this time your solution would be to get a sensor with a longer sensing range (10-12mm), and preferably a better quality one, and you quickly find that the $5-6 sensors don't cut it, and you have to spend around $25-30 for a decent sensor.

Well, that's all cut and dry... until you add a PCB heater like I have.  I have a PCB heater on top of print bed, and it has 3mm glass on top of it.  The minimum distance from my print nozzle to the metal print bed is actually 6.5-7mm.   That forced me to get a sensor that supported at least 10mm.   

Anyway, when I first tried it, it worked great, until I turned on the bed heater, and found that the sensor was very susceptible to electromagnetic fields.  Whenever the PCB bed power was on, it would scramble the sensor.  I don't remember if it was triggering to high, or too low, but suffice it to say, after a lot of trial and error, and way too much trouble that it was worth, I just took the stuff off, and went back to the original switch.

I still have the sensor on my Pritrbot Simple, but it's not in use, it too uses a standard switch, and manual levelling.

Anyway, even a tilt sensor is not much good in this application, for the aforementioned accuracy reasons. You'd need two sensors, doubling the maximum possible error. Much better to sense the distance directly, with something like an IR sensor:

https://www.filastruder.com/collections … ght-sensor

Next: you don't need leveling servos, your whole printer is a "leveling servo"! You can probe the bed at multiple locations and build a height grid, much like a topographical map. Then the Z-axis runs up and down while printing to put the bed in the right place.

To IronMan/pirvan/wardjr's point though, a bed should not need frequent adjustment. I generally adjust once every 100 prints or so.

I agree that, of course, starting with a level bed is best, at least with the technology of today.
Pirvan, you're right about the elf-adjusting Z axis to accommodate an unlevel or uneven bed, it makes goofy parts. And perhaps you've had better luck than I but when my bed was not level even a little bit, the first layer would stick on the close side and not at all on the high side. But maybe my bed was more unlevel than what you mean. My experience is, you need a correct first layer before you can have a good part. This seems particularly true if you're printing support since poorly stuck support tends to come loose and end up dragged around in balls all over the machine path.

However we look at it, gyroscopes be damned, bed leveling is very important and we should alway keep our eye out for a better, more fool-proof way to achieve and maintain it.

The best auto level feature is one that isn't needed.  Using software patches to compensate for crappy mechanical platforms is a last resort type of thing.

Nice to see we've come full circle with this conversation

A good platform that has been leveled to the nozzle properly is the way to go.  I have not had to re-level my bed for about 6 months...