I want: micro stepper motors for bed levelling

Hi all,

As I read more and more through this fantastic forum, I continously find bed levelling causes many headaches to many people (including myself!).

I have an idea... I would like to discuss it with anyone interested. I want to implement auto bed levelling using micro stepper motors.

Now let me explain my thinking.
There are many micro stepper motors available for very reasonable prices around the web. Some have small threaded shafts (like a fine pitched worm gear) that may be 10mm or so long.
I would like to put 3 or 4 of these under my bed so that that actual bed height is adjusted by altering the stepper motors.
Mechanically and electrically this is not too difficult to achieve. The software from my perspective is (how would I add something that that to Marlin?).
The thread of each stepper motor would be wound into a plastic (or other material) threaded spacer attached to the bed. Now if I rotate one of the steppers clockwise, then that part of the bed would move down. Rotate it the other way and it would move up. The print head could just be told to go to each corner (or micro stepper position) and told to level that position. It would be relatively quick and painless.

So if anyone has any ideas, or has already done it successfully or not, I would like to hear your thoughts. Something like this would make 3D printing much less painful.

I know the idea of software bed levelling many of us use already, but from my perspective is not an ideal solution. The bed is still not really level, it's just adjusting the print head for the unlevel bed.

Looking forward to anyones input.

Kind regards

I suggested some time ago that a CoreXY printer (which has a bed moving in the Z direction) could have the bed supported by 3 stepper motors driven independently, so that they could be used to level the bed. I am not aware of anyone having implemented this. To do it properly, swivel joints or some other mechanism (e.g. pin/groove/flat) would be needed to avoid the system being over constrained.

My solution to getting a level bed is to use a delta printer, which has a fixed bed that is inherently stable and level.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

If you had a bicycle that required you to reposition the handle bars or adjust the brakes every time you went for a ride, would you come up with a motorized mechanism that senses the poor position of the handlebars and rotates the fork in compensation? Would you add a longer lever to the brake so you could apply more mechanical force? Not likely. I'll bet you would figure out what the problem is and fix the actual problem instead of trying to work around it. So why do you accept as normal the inability of a 3D printer to maintain the bed level and zero position from one print to the next and try to work around that fundamental flaw by adding complications?

A mechanical system that requires frequent readjustment in order to perform its primary task suffers from a flawed design. There are three approaches to take in dealing with it. You can live with it, you can a apply work-around that does nothing to correct the flaws in the design, or you can fix the design by eliminating the flaws.

The first approach is unacceptable to people like you and me.

The second approach, which you have chosen, adds complication and reliability issues without addressing the root cause of the problem. How does the reliability of an electromechanical solution compare to a simple bed leveling screw? Considering the number of posts from people who can't figure out how to make their 2-motor Z axis work reliably (which is understandable- it is inherently unreliable), who is going to be able to deal with three more motors and the associated sensor(s) and electronics? How are they going to understand it, let alone fix it, when it eventually fails? Autotramming with an inductive sensor mounted on the extruder carriage already does what you want by using software to tilt the model to match the bed's tilt, without the added complexity of additional motors and electronics to drive them. As simple as it is, there is no shortage of posts in these forums about problems with getting autotramming to work reliably.

The third approach- building a printer that doesn't require frequent readjustment- is possible, but it requires spending more than $300 for the machine. You start with a rigid frame, use fully support rails or linear guides, and use a flat bed plate supported by a well-designed leveling mechanism. Where screws are used to provide motive force, you use lead screws, not threaded rods. This approach works well- I used it to build my printer (see the link below). In the last few months of almost daily use I have not had to adjust the bed level or zero position, even after transporting the machine laying on its side in my car.

Edited 2 time(s). Last edit at 07/19/2015 10:51AM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Yeah, good post DD!

I don't really understand why people give up with normal bed leveling and switch to auto bed leveling. If you can build a stable structure, then leveling the bed is quite easy. Even my first printer, which was built with stability in mind, hasn't needed to have the bed re-levelled in almost 3 years and I regularly remove the glass for cleaning and priming etc which doesn't effect it. I would have thought that a mechanically leveled bed would be superior to any bed which needed constant "pulsing" by the Z motor to maintain level height.

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Waitaki 3D Printer

I looked into the micro-steppers, you can get those for $4-5 plus basic $1-3 driver, so it's doable but maybe not worth the effort. I was looking into making a big printer at which point I might do auto-leveling just because I need two z-motors anyway if I go to 3 I might save some effort.

But much of the benefits of auto-leveling could be achieved with just the sensor. Imagine instead of playing around with the paper, you just have your printer probe the board and software tells you "turn left screw x turns left, turn right screw y turns right, back screw .." etc. That helps dummify the system.

In my experience with a moderately stiff frame (solidoodle 2) I rarely if ever need to fix my bed level. And if I do it's a tiny tweak that I notice on the skirt of my 1st print level (section A,B, or C has a taller bead= need to adjust that section.) So all in all it's a very easy fix.

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waitaki
Yeah, good post DD!

I don't really understand why people give up with normal bed leveling and switch to auto bed leveling.

Its an education problem. My first printer (i3) was ready made, built by someone else (badly) and I had no idea how to level the bed properly, it had no bed levelling screws, the heatbed was bolted direct to the y-carriage. I started inserting washers at one corner or another to try to get it level, got nowhere amongst all the other problems, and gave up and installed a proximity sensor.

Now I understand how it works and how to fix problems I'm going back to decent adjustable, bed levelling screws, and just using the sensor for z homing instead.
Perhaps on the i3 it would be best to have one more powerful z motor and pulleys with a belt, to prevent the left and right motors from going out of sync, so bed level doesn't drift as much over time.

As for my Kossel Mini I installed FSR's after trying in vain to manually calibrate it with inadequate results, I decided that it would be easier to install a z probe and auto-calibrate than do it myself. And it works very well now. Since I have a z probing solution, I figure I might as well do a g29 before printing, I probably don't need to, my bed level results show very little variation in height across the bed, but it does the autolevel probing, whilst the extruder heats up so it's dead time anyway.

I think its a combination of not knowing how to do it in the first place then deciding the technological solution is easier and way cooler than manually adjusting screws. As had been said before if the frame is rigid and the bed orthogonal and everything is made of solid stuff that won't move much over time then you don't need it but $300 printers have few or none of these features.

With most printers you want to make sure the bed is at print temperature before you run the leveling routine. The bed plates tend to bow a little because as the bed heats and expands it puts pressure on the leveling screws which then force the bed to bow (something has to give).

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]