Best way to set Z-axis zero position?

Hi,

I'd appreciate some advice on how people set their Z0 position. I'm familiar with using a piece of paper and dropping until resistance is felt but thats a bit subjective and I think I may be over setting the position.

I've an Ormerod 1 with DC42's upgraded sensor and his 1.09k firmware. The bed is physically set to within 0.05mm across the four corners and centre before any sort of logical calibration.

For setting Z0, I've been putting a sheet of 80gsm paper under the nozzle at printing temperature and dropping the head until I can just feel resistance. If I then drop it a further 0.05mm I can still PUSH the paper with resistance but starting to feel a vibration. If I drop it a further 0.05mm I can then only PULL the paper to get it to move, not push it and feel a lot of vibration.

Assuming the right answer if one of those three to set Z0 which do people use?
Secondly against your Z0 calibration method what first layer height do you use if you have a 0.5mm nozzle?

Dave

Z=0, by definition, means, that the nozzle has to touch the print bed. If you can put a piece of paper between the nozzle and the bed at Z=0, your calibration is wrong.

The best way to calibrate Z=0 is not to calibrate Z=0.

Take something flat and rigid with a known thickness (I use 0.4mm business cards) and use it to calibrate your known height (e.g. Z=0.4). Your height is right when you feel the nozzle slightly touching it.

Quote
Fatlab
For setting Z0, I've been putting a sheet of 80gsm paper under the nozzle at printing temperature and dropping the head until I can just feel resistance. If I then drop it a further 0.05mm I can still PUSH the paper with resistance but starting to feel a vibration. If I drop it a further 0.05mm I can then only PULL the paper to get it to move, not push it and feel a lot of vibration.

Assuming the right answer if one of those three to set Z0 which do people use?
Secondly against your Z0 calibration method what first layer height do you use if you have a 0.5mm nozzle?

Dave

The right one to use of those three is the one that gives you good first layer adhesion without the head being so low that the filament can't escape and the extruder skips steps or grinds through the filament. I have found that the nature of the bed surface affects the amount of grip substantially, So if you change the bed surface from e.g. plain glass to PVA glue, you may need to adjust the amount of grip you look for.

I know what RFZ is getting at, however in practice the print head assembly has some elasticity, so it is perfectly possible to use the paper method to get a good Z=0 setting. When I want an accurate measurement, I adjust the head until I can just slip a 1mm feeler gauge under it, then I know that height is Z=1.

With a 0.5mm nozzle, I usually print at a first layer height of 0.2mm (the same as the remaining layers). However, if the bed isn't perfectly level, then it is easier to use a first layer height of 0.4mm and revert to 0.2mm for subsequent layers.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

As RFZ says, why bother with Z=0 since you will never print with Z=0.

Decide on what you will use most as your first layer and calibrate to that. A set of feeler guages will not cost you much at any car parts store and you will get accurate guages for many heights, I use a 0.2mm feeler guage and calibrate my machine with the height set to 0.2mm.

It is worth noting that you should calibrate to a value that is an integral of your leadscrew and stepper motors steps, there is a calculator on the reprap pages to get this.

OK, you calibrate to Z=0.5mm. Now what? Where do you enter that 0.5mm offset so that the printer gets the first layer right?

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

You can enter that slic3r, z offset -0.4mm or thereabouts depending on your bed adhesion. Other slicers are available. If you have a z probe then you set the probe, then autolevel, then measure the clearance at the nozzle and either change your configuration.h depending on the probe z offset or make the change in slic3r. Your configuration needs to allow positioning the nozzle below z=0 which mean altering the travel limits after homing.

Edited 1 time(s). Last edit at 11/19/2015 03:10PM by DjDemonD.

I use whatever gives me a first layer height of 0.33 when printing it with 0.33mm. I usually measure the brim with calipurs. Use whatever method gives you consistent and repeatable results and get a print done, adjust from there relative to the last print. Auto bed leveling works well for me. I've managed a repeatability of 0.01 to 0.025mm in the center and corners respectively. Then I adjust the z offset on the lcd control panel. This is only necessary when I change plates or plate material/height.

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Kind regards
Imqqmi

NFAN CoreXY printer:
[reprap.org]

Use a 0.004" or 0.104 mm feeler gauge as your zero point. That way your nozzle won't drag across your plate when you home and then disable steppers to pull your print out. If your first layer is .2 or .3 mm and you set your first layer extrusion at 150%, you'll get a nice well-adhered first layer AND you don't have to fool around with all the Z offset BS. The feeler gauge is stiff enough to easily slide in the gap and get a good feel for whether it's right or not. Paper is, like someone said, too subjective. Go to the auto store or Harbor Freight and get a feeler gauge set and be done with it.

so if the bed is touching because my z offset is .2 should i try .4 or 0 to -.2?

Quote
tjnamtiw
Use a 0.004" or 0.104 mm feeler gauge as your zero point. That way your nozzle won't drag across your plate when you home and then disable steppers to pull your print out. If your first layer is .2 or .3 mm and you set your first layer extrusion at 150%, you'll get a nice well-adhered first layer AND you don't have to fool around with all the Z offset BS. The feeler gauge is stiff enough to easily slide in the gap and get a good feel for whether it's right or not. Paper is, like someone said, too subjective. Go to the auto store or Harbor Freight and get a feeler gauge set and be done with it.

I prefer not to have my nozzle set to Z=0, as it drags across the bed surface, make sure it is always above the bed by a fraction of a millimeter.

Using a uxcell 0.02-1.00mm Metric Gap Measure Feeler Gauge I set Z=0 nozzle height to .02mm. As I print at .10mm or .15mm on many models.

LeaveThickness (mm) : 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.15. 0.20. 0.25, 0.30, 0.40, 0.50, 0.75,1.00

How about doing the offset in firmware? Like use a piece of paper/feeler gauge to set set the nozzle at a particular height, and have the firmware set to that height. That's the way I do it with Marlin, so it reads Z=0.10 when the switch is triggered.

If you're concerned about removing a print from the machine, at the end of the print you home X and Y (or send Y to max, depending on the machine's configuration), but never Z, otherwise the nozzle will probably crash into the print.

AFAIK, every firmware out there will set the nozzle to a mm or so off the bed after an XYZ homing instruction. If you set it to home X and Y first, how/when is it ever going to drag the nozzle across the bed?

What's far more important than the zeroing is how you do the zeroing. What I mean is that if you use a 0.7 mm pitch screw to adjust the zero position, one turn of the screw moves the bed 700 um, the equivalent of >3 typical print layers. That means making fine adjustments such as 50 um (that you might typically need to make) requires a very tiny fraction (1/14) of a turn of the zeroing screw, and the result is overshooting your target. In my latest printer I made a lever with a cam to bump the zeroing switch. The assembly reduces the effect of turning the screw by about 8x. So one turn of the screw moves the bed about 100 um. Making a 50 um adjustment takes about 1/2 turn which is easy to do without overshooting.

See: [vimeo.com]

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]