Autolevel Z height

Hi, I am fairly new to marlin and prusas, however I have experience with old markerbot's firmware. I installed an induction probe in my hictop prusa i3 (it was the old model without autolevel from factory). Setting the height seems to be quite an art, in all my attempts I have been scratching the bed or roaming miles away the bed...

1) Is there a quick way to force some Z offset from the printer itself and save that configuration? In my old makerbot there was an offsets menu

2) Which is the normal procedure when printing in marlin? should I always select auto-home first?

thanks!

If you go into Marlin's configuration.h file you should find the following lines:

  #define X_PROBE_OFFSET_FROM_EXTRUDER 0
  #define Y_PROBE_OFFSET_FROM_EXTRUDER 20
  #define Z_PROBE_OFFSET_FROM_EXTRUDER -0.6 // increase to move hot-end closer to bed

These define how far the Z probe is from the nozzle, in the X, Y and Z planes.

Set values to suit your own machine, then recompile and upload to the printer.

Edited 1 time(s). Last edit at 01/26/2016 10:15AM by David J.

Thanks! however I was looking for a way to do this in the machine itself, but I guess I can upload the firmware and test until it prints correctly.

The method where you alter the z offset, print and then go back and try again works but its tedious (especially with ABS and the long waits for bed to warm up etc..). Once you've done g28 the print head (or probe) should be at bed centre. Send command g92 z10 which makes the printer think its at z=10, so you can move it downwards. Do so until you have a 0.1mm or paper thickness or feeler gauge under the nozzle and measure the amount it has dropped. Go in small increments such as 0.1mm, to avoid a head crash. Then use this value in your offset in the code above.

So I did g28. The probe I'm using is a capacitative probe. I did g92 z10, then lowered the nozzle until it was firmly gripping a piece of paper. The amount I lowered it was 2.4mm so I went back to the firmware and entered z offset from nozzle 2.4mm (if your probe is lower than your nozzle use a neagtive number). Then did g28, g29 and went to bed centre. Now when I lower the nozzle to the bed the z coordinate on the LCD is z=0. You might want to add +0.1-0.2mm in your slicer to allow for an acceptable first layer.

You could also try babysteps, you can enable this in marlin - I think its in configuration_adv.h. You should then be able to access it from your printers LCD. This allows you to slightly lift/lower the z height during printing such as when printing a skirt before the object begins to print. Just set the feedrate quite slow and print a big wide skirt to give yourself time to access the menu and jog it up or down to get best first layer adhesion, by the time it starts printing your object it will be correct . You should then be able to do m500 assuming you have eeprom enabled and it will save your setting for next time. I haven't tried this yet as I did not have the latest Marlin version until yesterday but it will save a lot of time if it works.