How to set the Z axis home?

Hello All

I have been wondering for some time now how one would go about homing the Z axis... or at lease setting the Z-Axis home in the first instance.

I had imagined the home position would place the nozzle over the cut-out in the bed to prevent a head crash. It turns out this is not so.

Further, the Z axis will not move into negative territory (i.e. lower than home) so I am guessing Home will have to be just touching the bed. Is this correct?

Thanks

Edited 1 time(s). Last edit at 12/28/2010 04:15PM by AgeingHippy.

You may have to change the wiring of the stepper motor to enable it to go down and touch the bed.

A common microswitch can be used to set the specific height, at least that is what i'm going to use.

Use the MIN endstop as the input to the stepper driver.

I am afraid you misunderstand my question Grogyan.

I wonder where to set the Z home position. Is it where the nozzle just touches the bed?

Cheers

Its should be just under a single layer height above the bed. Don't let it touch.

Thanks Andrew

Does the first layer then get printed at the Z=0 home position?

Cheers

Hello..

I set mine so I can slide a peice of paper with some drag beween the nozzle and the bed..As for leveling I just move the x/y to diffrent places and use the paper under he nozzle, after a few mins you should be setup.

Auzze

This week, I got my heated bed working. I had carefully adjusted my bed so that I can slide a piece of paper (about 0.1 mm thick) between my heated glass bed and the extruder tip. But when I printed, the first layer was coming out too thin: 0.2 instead of 0.4 mm. I did this while the bed was set to 70C. I was puzzled until I read a topic in this forum where someone pointed out that the PTFE plastic in the extruder will expand when heated and reduce the bed height. Duh! I guess in my case, the height goes down by 0.3 mm so I should use 3 sheets of paper to set the clearance and try again.

Dear all,

Thank you for replying to AgeingHippy above, I had the same issue and I have now carefully calibrated my Z-axis home position to be 1-sheet above the bed plate and carefully checking that it is level XY-wise.

Alright, then I turn on the machine, I do a few tests on the extruder, then back to "home" again to prepare for printing, and there all hell break loose. My aluminium plate has moved a little bit possibly, or I was not exactly in "blocked" position for the Z-optoswitch when I did the calibration in the first place. Result is either an extrudeur a few mm above the plate or a big crash into the bed.

So my question is how do you actually calibrate the Z axis endstop ? Do you play on the optoswitch position, higher or lower with maybe a few washer ? Or do you play with the Z elevation of the bed ? Or with the aluminium thin plate that goes into the optoswitch ?

Thanks for the help

Matthieu

I have changed my procedure a little bit. After I level the bed, position the extruder raise a few mm in the middle of the bed. Heat up the bed. Instead of adjusting the z home position with the tip cold, I now heat it up to operating temperature and wait about 5 minutes or so with the extruder raised a few mm from the bed. After clearing plastic from the tip, I slide a piece of paper under the bed (verify the thickness with a caliper first), home the z-axis and then nudge by 0.1 mm. I then pull and push on the paper a little. If it's stuck, I raise the optoswitch by turning the 3 mm socket screw counter clockwise. If it's too loose, I lower the optoswitch by turning the screw clockwise. Then home and nudge the z axis again and repeat the paper test. I don't bend the endstop flag as long as the bed can still be adjusted with the optoswitch adjustment. There should be tension in the plastic springs on the endstop and on the bed or it won't be reproducible.

You might want to check reproducibility by raising, homing and nudging your z-axis a few times and checking with the paper. You might also want to move the x and y around. Perhaps something is loose.

I like to print a single-walled square object with a skirt (or outline) option turned on in skeinforge. Then I can use the outline to measure the actual layer thickness and make fine adjustments if needed. If it's too thick, you can make the adjustment by software in Skeinforge bottom option by changing the Altitude to the difference of the set layer thickness and the extruded plastic. Some people like to extrude the first layer at a fraction of the layer thickness to make sure the plastic sticks to the bed. I prefer to have the same thickness from the first layer.

Thanks for the input. I'll try that as soon as I can get my extruder properly extruding

My question is tangential to the above discussion - how does the software know how far it is from home to the bed? I can't physically move my limit switch (long story - experimental machine) but when Z is at 0 the tip is a full quarter inch above the bed.

I have googled everything I can think of to get the answer but it seems to be one of those magic things that everyone but me just knows.

I'm running kliment-Sprinter-52f7f30.

I have looked at the calibration scripts out of RepG and it looks like G92 is the key but sending G92 Z0.0 then sending it home and sending it to 0 (G1 Z0 F1800.000) doesn't seem to have the desired effect.

Plus, how do I save the new value to eeprom such that it keeps it through the next cold start? The RepG script uses M131 but Kliment-Sprinter doesn't implement M131.

Thanks for your help,

DougM

You're going to have to figure out how to lower your endstop, lower your nozzle tip, or raise your bed so that the nozzle can be within a layer thickness from the bed surface when you home it. Ideally, the nozzle need to be one layer thickness away from the bed when it extrudes the first layer. Most firmware prevent you from going lower than the endstop switch. Of course, you can edit your firmware to ignore the endstop but I think this is a risky thing to do.

Quote

I have looked at the calibration scripts out of RepG and it looks like G92 is the key but sending G92 Z0.0 then sending it home and sending it to 0 (G1 Z0 F1800.000) doesn't seem to have the desired effect.

A G1 Z0 after a G92 Z0 has no effect by design. G92 sets the position to wherever you are and going to Z0 after that ... well, you're already there. What you probably want is a G92 Z25 and G1 Z0.

Quote

how do I save the new value to eeprom such that it keeps it through the next cold start?

You don't. Turning the controller off makes it loosing the knowledge about its position, so it doesn't know where to move to go to zero. That's why you have to find the endstops after each power cycle.

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