No more manual bed leveling!

Brent Dowell

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As you start printing, you will find that bed leveling is one of the most critical things to get right.

Too high, and you end up with adhesion problems, spaghetti and failed prints. Too low and you crash into the bed. Uneven, and well, you get uneven prints.

Well, Thanks to hep from darren, we've both got our auto bed leveling sensors working and I have to say I'm loving it.

We are using a capacitive sensor since it's supposed to work with glass beds better. I print directly on glass and really haven't had any kind of issues with adhesion.

Sensor : LJC18A3-H-Z/BX Make sure is is the NPN NO (normal Open type).
If you are not using glass, or pei, you can look into using an inductive sensor. The trade off is that you might need to adjust the offset for a capacitive sensor as it is supposed to vary a little bit due to heat and humidity.

Firmware : Skynet 2.3 https://www.facebook.com/search/top/?q=skynet3d firmware development
Bracket : http://www.thingiverse.com/thing:1907394

Wiring diagram:
We've found that we are getting better results by powering the sensor with 12 volts instead of 5. The problem with that is that you don't want to feed that 12v of power into the z stop connector on the control board, as that is running at 5v. You don't want to let the magic smoke out.
Darren can probably explain this better, but basically wev'e wired a couple of diodes inline to prevent the 12 volt current from going across the into the signal pin on the control board. When the sensor senses the bed, it closes the connection, and from what Darren tells me this lets the signal get pulled to ground.
All I really know right now is that this works. The guy in charge of skynet claims you can run it off of 5 volts, in which case you could just hook up all 3 wires to the z stop pins on the board. The are also other wiring diagrams that use resistors to create a voltage divider circuit. So far, I've been using this and the magic smoke is still in the board.

capacitive hookup diagram.png



Steps:
1) Print a bracket of your choosing.
2) Install the sensor
3) Grab the skynet firmware and flash your control board. It's pretty straighforward and the instructions for doing it are included in the download.
4) Fool around with the sensor to get it to sense your bed. You can use a combination of adjusting the height of the sensor in relation to the nozzle and turning the set screw on the sensor to adjust it's sensitivity.
5) Use the z control buttons on your favorite printer control software to adjust the nozzle down to where it squishes a piece of paper just right. Just like you did when you used to level your bed manally.
6) Record that offset (should be a negative number. Mine is -1.45 right now) and enter that into the printer as the z-offset.

Thats pretty much it. You can level the bed on the printer using the lcd screen and the buttons to select it, but what I've done is to just add the bed leveling as part of my start script. It gets prepended to any gcode that I send to the printer.


Here's what I have my starting script set to in Simplify 3d. Just like you probably already use the G28 to home everything, G29 will run the auto bed level. Skynet is defaulting to a 9 point level, which might be overkill. I know darren changed the config for his firmware to do a 4 point level. I just like to watch the sensor fly around the bed before it prints.

You can see some other extra commands I have in there that basically prime the nozzle by running a couple of lines along the y axis to get things ready to roll.

Code:
G28 ; home all axes
G29; auto level bed
G1 X20 Y5 Z0.2 F3000 ; get ready to prime
G92 E0 ; reset extrusion distance
G1 Y150 E20 F600 ; prime nozzle


G1 X25 Y5 Z0.2 F3000 ; get ready to prime
G92 E0 ; reset extrusion distance
G1 Y150 E20 F600 ; prime nozzle

Here's a print I did using the wood fiber filament of a buddah body with a baby groot head. The filament feels a little bit like balsa wood, probably because I printed this with only 10% infill, so it is really light. But it seemed to print pretty well actually.

buddahgroot.jpg
 
Thanks for the info, Brent.

Am I assuming correctly that, with the Skynet routine, the position of Z at the various points is logged and each print is adjusted based on the auto-leveling info?
 
... We are using a capacitive sensor since it's supposed to work with glass beds better. ...

Well, I guess I might have messed up. The sensor I got is inductive but is supposed to work up to a 4mm distance. I'll have to hook it up to power and see how it works holding it in my hand as a test and see if it triggers.
 
Well, I guess I might have messed up. The sensor I got is inductive but is supposed to work up to a 4mm distance. I'll have to hook it up to power and see how it works holding it in my hand as a test and see if it triggers.

You didn't mess up. An inductive sensor is perfectly fine. It's just supposed to work on the aluminum bed, maybe with tape on it? I'm not sure. But I've been printing on glass and for glass they say to use capacitive. I'm not going to pretend to know why, lol.
 
... I've been printing on glass and for glass they say to use capacitive. I'm not going to pretend to know why, lol.

The sensor I ordered was one I saw that was recommended for the A8. As I read more about the printer, the use of glass on the bed kept coming up, so I ordered a hunk to fit the A8. I've placed an order for a capacitive sensor.

An inductive sensor works when it's close to a metallic object, so that's probably why it's not recommended for use with glass. There are inductive sensors that use a more focused field that might work well with glass, but I don't have one of those!

Ah, well...live and learn. :rolleyes:
 
The sensor I ordered was one I saw that was recommended for the A8. As I read more about the printer, the use of glass on the bed kept coming up, so I ordered a hunk to fit the A8. I've placed an order for a capacitive sensor.

An inductive sensor works when it's close to a metallic object, so that's probably why it's not recommended for use with glass. There are inductive sensors that use a more focused field that might work well with glass, but I don't have one of those!

Ah, well...live and learn. :rolleyes:

Well, Let's just say I have two other sensors that I'm not using. One is PNP NC, and the other is an inductive, in case I change my mind, lol.
 
The sensor I ordered was one I saw that was recommended for the A8. As I read more about the printer, the use of glass on the bed kept coming up, so I ordered a hunk to fit the A8. I've placed an order for a capacitive sensor.

An inductive sensor works when it's close to a metallic object, so that's probably why it's not recommended for use with glass. There are inductive sensors that use a more focused field that might work well with glass, but I don't have one of those!

Ah, well...live and learn. :rolleyes:

There have been folks that say you can put foil on the glass to sense as long as your print doesn't go into those areas.
 
You mentioned that before and I've read it elsewhere also. That method precludes measuring the center of the plate, though.
Well, that does make sense. Btw, I haven't chimed in yet much as I've been having troubles getting the auto level to work. Doing some comparison with Brent, it's looking like it may be due to the way the Y belt is attached. They give you 4 little plastic pieces to hold that belt and I only used two. Looks like two may be needed to keep the belt parallel to the rails, shimming them down, but I need to test this yet. I have two corners on the auto level that are consistantly high. So when the bed reaches the end, its pulling down on the belt, causing the bed to tilt up in those areas. At keast that is the theory. ;) Will keep you posted, but use two as shims if you havent and make sure the middle bar is downward on the H frame when mounting it.

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