Poor Man's Auto Bed Leveling

Hi everyone my name il Lorenzo, i'm an Italian engineer and RepRapper, i have to say thanks to this forum for all i've learned, today i want to contribute in some way. This morning i was trying to get a print done but the bed wasn't calibrated so i've started to get the calibration as good as i can but after half an hour of screwing and unscrewing i've got tired and i started to think about something that would calibrate the bed but i haven't nothing like spares endstops o servos, so instead of tearing down some of my projects i've decided to make a Auto Bed Leveling in the poor way.
You only need:

• 1 Relay
• Some wire
• Something where you can get a copper foil (Single Sided PCB, Copper tape...etc)
• Some glue that is heat resistant for gluing the copper foil to the bed.

Nothing else. Now, to get this working you have to make sure that the shell of heating cartridge of the printer is connected to the +12 rail, if not just reverse the wires, so the idea is that the cartridge is connected to the heating block that is connected to the nozzle tip and all of these thing are made of metal so are conductive, if you stick some copper on the bed when the nozzle touches the bed it will close the circuit. So you have to stick to the bed 4 pieces of copper and solder a wire connecting all the four together, make sure that the wire is long enough to reach the RAMPS, you can tie that together with the heated bed wires, after that, on the RAMPS side connect the 0V rail to the coil of the relay and the wire coming from the copper tape to the other side of the coil, make sure that when the extruder touches the tape the relay turns on.


(sorry for the bad quality pic)

Now you encounter the first problem, the brass tip of the nozzle could be covered by plastic, you can heat the head to 100-150C and get rid of it, you also have to modify the starting gcode of the printer for heating the extruder to 150C then do the bed calibration and finally start the print.


(the four copper squares glued with epoxy)


(the jungle of wires, you can notice the green relay glued to the glued lcd that is glued to the aluminium, i love hot glue...)

After verifying that the relay works as expected you can connect the NC (Normally closed) side of the relay in series with the Z endstop, so you have a situation in witch if one of the two endstop is pressed the RAMPS will read as the endstop Z is hit, the rest is configuring all the firmware to get the right spot and then you are ready to go.



And here is a video of the entire assembly working.
Video
For any question i'm here!

Edited 2 time(s). Last edit at 09/28/2015 09:42PM by Lollokara.

You have made a very interesting printer design and leveling system! We had a CNC router at the makerspace that was made from a surplus XY table and moved liked the bed in your printer.

I noticed there are 4 leveling screws near the corners of the print bed. When you try to level a bed using 4 corner screws, what happens when you tighten just one screw? A stiff bed wants to rock on the diagonal line between the two adjacent screws. The diagonally opposite corner wants to go up but can't because its screw stops it, so the bed tries to bend on the diagonal instead of rocking. Since everything is flexible to some extent, both the bed and the undercarriage bend. If the bed is stiffer than the undercarriage, the undercarriage bends more. If the bed plate is more flexible, it bends more. How can you level the bed by bending it and the undercarriage? I believe this was the true nature of your original bed leveling problem. It is a problem in every printer that has 4 bed leveling screws.

A properly implemented 3 point bed leveling scheme will actually level the bed without bending it or the undercarriage. 3 screws and springs are a few cents cheaper than 4, and no level sensors are needed. THAT's a true poor man's bed leveling system! No firmware or gcode tweaks are necessary. See step 7 in the link in my sig, below to see an example of a 3 point bed leveling system done right. This system works so well that this weekend I tweaked the level/zero of the print bed for the first time since January, even though the printer is in almost daily use and has been transported laying on its side in my car on at least 4 occasions.

---

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

Well yep you are right, a 3 screws system would be better, the only problem was that the aluminium plate was already designed with 4 screws and instead of drilling another hole and modifying everything i just came up with a modification that is even more precise than a screw adjustment. Regarding the cnc, the design of this printer is made for becoming a cnc, if you look carefully on the pic there is a proxxon drill and the drill bist on the top of the printer, i use this cnc for engraving (metal, wood and etch circuits). We can say that is an all in one printer.

If the shell of your heater cartridge is connected to +12V then I suspect it is faulty. I would expect the shell to be isolated from the wires. I just tested 3 different cartridges, and they are all isolated.

---

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].

Well... Good to have a faulty one... Well you can still do the "trick" you just have to bring the +12 rail or +16 in my case to the extruder