Kobra Bed Leveling System

thingiverse

I started having problems with uneven 1st layers, especially on large flat prints on my new Anycubic Kobra. I did some research, created a Leveling Test, and wanted to share how I fixed the problem. *There are other ways to do this, but the current Firmware on my Kobra would not allow me to use any other method than the following. I use Repetier Host to control my printer, so I connect it to my printer right after turning the printer on. you will need a Host Terminal to do some of the things I'll be explaining. After connecting to Repetier, I start by running the Automatic Bed Leveling from the LCD. The machine should Home all axis, wait for the Bed and nozzle to Heat up to PLA temps, then start probing in a 5 x 5 pattern across the whole bed. Then the Machine Homes all Axis again which lands the probe in the middle of the bed. From the LCD choose Z-offset. Get a piece of paper under the nozzle, and hit the (-) sign to lower the nozzle until it puts some pressure on the paper, but you can still slide it out an back under. Then Hit "OK" Here's the custom part: Using Repetier Host, raise the nozzle 1mm in Z (to not scrape the bed). Use the X and Y controls to move the Nozzle to the farthest right you can, so the nozzle is right at the edge of the bed, and the probe is off the side. Lower the nozzle by 1mm in Z and get your piece of paper out and slide it under the nozzle. Raise or lower the nozzle in Z by small amounts. 0.1mm or 0.01mm until you get the same tension on the paper as you did in the center of the bed. In the Terminal, type: M421 C and hit enter. This command Adds its current position to the Bed Leveling Mesh that it created when probing. It was unable to reach this area because of the offset of the nozzle from the probe, and this will help the machine to calculate a more accurate "Map" of the contours of the bed. Now raise the nozzle in Z by 1mm, and move the nozzle in X by 50mm towards the back edge of the bed, and do the paper trick again and save the point with M421 C. Do this all along the edge, move to all 4 corner and do the same, making sure to type M421 C after reaching the right nozzle height with the paper. Add as many points as you want. If you find that there are pot holes or abnormally high areas on you bed when you try to print a large flat first layer, make note and go to these areas to add them to the Mesh with M421 C at any time Make sure that once you've manually added all these points to the mesh, type: M500 in the Terminal and hit enter. this will save your changes to the EEPROM (Memory of the Machine) and it will be able to use this Mesh every time you print. Another Tip: When you start a print, the machine needs to Home all axis before starting. however this disables Bed Leveling Mesh, and needs to be turned back on immediately after Homing. if the machine moves anywhere before you turn BLM back on, it will assume that it should place the Mesh right where it is. this could offset the mesh and ruin your leveling efforts. In your Slicer settings, add this to your Start Gcode: G28 ; Home all Axis M420 L; Load Bed Leveling Mesh M420 S1; Use Bed Leveling Mesh *This will turn BLM on before every print you slice* Now it time to test the accuracy of your Mesh. Slice the file:".15 Bed Leveling X.stl" with a 0.15 first layer height, and print. (This is made to fit a 220 x 220mm bed, but can be scaled down) I print this from Repetier, and not from the SD card, just for speed. once you start the print, go to the LCD, and hit "Prepare" - "Leveling" - "Z-offset", and Watch carefully to see how it lays down. If there are Ragged edges on the plastic as it comes out onto the Bed, your too close to the bed. - Hit (+) once then hit "OK" to raise the head by .05mm If it's not sticking or comes off and sticks to the nozzle as it passes by, your too far away from the bed. - Hit (-) once then hit "OK" to lower the head by -.05mm *This kicks you back in the menu, and you will need to hit "Z-offset" again. if you don't hit "OK" after changing the Z-offset height, the head did not move. If you make a change to the number but decide not to change the height, you can hit the Back Arrow to cancel. If you've got smooth plastic going down in some spots and ragged or not sticking in others, even after setting the Z-offset, Make note of these spots. After the print, Home all Axis with Repetier Host (or whatever your using). Then maneuver to those trouble spots, make sure your nozzle is clear of plastic, and manually add Mesh Points with paper and M421 C like before. Make sure to send M500 after to save to memory. Run the Bed Leveling X again. it should be getting better. Another problem I had was that as I was adding some mesh points I found that I could not lower the nozzle far enough to make good contact with the paper because I was at Z0 based on the probe distance from the bed. (mine is inductive). So I turned the screw on the top of the probe, clockwise about 1.5 turns, then running the whole process of Auto Bed Leveling, then Adding more points, and setting the Z-offset, now I could lower the nozzle far enough to get to those low points and save. One more tip: Instead of using the LCD to change the Z-offset, which only allows 0.05mm changes, use Repetier and send this command with your own number while the "X" prints to change it on the fly. M851 Z-1.53 This example changes the Z-offset to Negative -1.53mm. I found that sometimes 0.05 is too much, and using this command you can choose any number of adjustment to get it perfect. (this sets the Offset distance in Absolute mode, not Relative mode.) *To help speed up the process of sending repetitive commands thru the terminal, I often copy and paste the text I need to send. For example, I move to the location I want, check with a peice of paper, then right-click and paste M421 C and click Send, then move to the next point. this keeps my left hand free to hold paper and not need to type over and over.Same with Z-offset while printing M421 C ; adds a mesh point at current location M851 Z-x.xx ; sets Z-offset for now and later prints M500 ; saves settings to memory Print Settings: Machine: Anycubic Kobra PLA First Layer Height: 0.15 Temp: Hotend -210c, Bed-60c Bed Size 220 x 220 mm infill: doesn't matter