Print head fine for autohome but to high during print.

I have autohomed and leveled the bed but when it goes to print an item it is two high and drops the plastic onto the bed.

optional question, how do I get it to drow that little border around what it is printing to make sure it is extruding?

Thanks

It sounds like your z-offset is incorrect. There are three places you probably want to check. The firmware has a z-offset in configuration.h. If you have EEPROM enabled in your firmware, your printer is also keeping a separate z-offset. Only one of these should be active and I believe the EEPROM always overrides the firmware value. These both change the physical location of z=0 on your machine.

Finally, there a completely different z-offset in some slicers (definitely in slic3r). This does not change the z=0 position, but rather the layer heights in g-code. For example a 0.2mm first layer with a -0.1mm slicer offset will start the print at z=0.1mm.

Partial optional answer. At least in slic3r it is called a skirt: http://manual.slic3r.org/expert-mode/skirt. Haven't used the other slicers much, but pretty sure it is still called a skirt.

I'm using Slic3r, the older version that Colin recomends. With all the default settings. I am printing from SD card using the firmware that is loaded per the build guide.

I think you are saying that I should look at the z offset in the slicer as well as the control panel on the printer and make sure they are both at 0?

Actually, I should ask a clarifying question. When you say auto home are you talking about having the machine home to a microswitch mounted to the frame (default for Makerfarm kits) or Auto Bed Leveling (usually with a switch attached to a servo or possibly a non contact sensor on the print carriage)?

If the first you need to turn the screw that hits the microswitch such that nozzle homes just above the bed. A lot people use a piece of paper under the nozzle as a gauge. There should be a bit of friction on the paper between the nozzle and bed when the home position is right.

If you are using an auto bed level (ABL) setup, the z-offset in the control panel should be equal to the distance from your nozzle to the bed when the ABL switch is just clicked. That way the machine know how much farther to move down once it puts the switch is closed. There are some good explanations for how to find this number but I can't get to them to get the links from work.

The slic3r setting should nominally be 0, but can be useful sometimes for quick modifications.

Yes, I have the default setup with the microswitches that I am homeing to, I have leveled it with a piece of paper. When I go to print the head lifts up about a mm above the glass

Ok. On the LCD check "Control" > "Motion" > "Z offset" to see if it is something other than 0. Also check slic3r "Printer settings" tab and "Z offset" for something other than 0.

Maybe also try a manual

Code:

---

G1 Z0 F60

---

in a terminal and see where it goes.

If you are using the most up to date 1.0.3 dev version of marlin abl is messed up, as adding the raise before retracting the probe stuff messed up the offsets. you should roll back to the marlin 1.0.2 tag.

I've noticed a similar thing here, the work around that seems to solve the issue is to ensure the z axis is a few mm above the end stop switch when the auto home is performed. This causes the z axis to come down to the switch, then back off then slowly come back down onto the switch. Before starting the print, again ensure that the z axis is a few mm high and the process repeats when the print starts and calls for the home routine. Hope that makes sense?

As an aside does anyone know which module the home routines are in? I'd like to see if it is possible to make some changes to ensure the routine always brings the z axis down, back up and then a slow descent to get to 0.

Turns out my glass was lower in the center of the bed, but it cracked all the way across yesterday so now I need to get some more, think I will look for something thicker this time. Only stuff I could find w/o going to a specialty store was 2mm thick.