Start Z height automatically

Hi everyone. I'm new here, please be gentle.

I've gotten myself a emaker huxley and now feeling the pain of constantly trying to calibrate the right Z home/height appropriate for the first layer.

From most guides on Z calibration I've seen, it says to "Home Z" to a first layer height. So basically to adjust the endstop switch height and bed combo until the nozzle is at slightly less than the layer height from the bed. At current layer heights I'm using (0.25mm) it means to visually calibrate the distance to 0.2mm??? I think that's just insane.

So my question is, why can't we really "Home Z" so that the nozzle actually touches the bed (gently, of course). At the start of the print, we can then have the printer first go to the appropriate height (0.2mm or lesser) and have perfect first layers? This should be trivial because the Z resolution is much much higher then the other axis.

Sorry if I'm not making sense. Thanks!

You can also do that. But since it's easy to make a mistake and not have the bed perfectly level, I think that approach increases the chance of the head crashing on the bed. I like to use a sheet of paper which is around 0.1 mm as a feeler gauge to set my z home clearance with the nozzle hot. If you do it cold, then there's a good chance that the head will crash when hot due to thermal expansion. Before that, I level the bed using the same sheet of paper but it you're still very far from level, I roll a round rod that I've measured with a caliper between the bed and nozzle. Usually, I only level the bed once unless I disassemble the bed again.

To compensate for the clearance, I set the Bottom feature in Skeinforge to an Altitude of -0.1 mm and a Additional Height over Layer Thickness of 0.5.

I always calibrate zero to the bed, and disable negative z travel.

Otherwise it's easy to make the software crash the head accidentally.

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I set endstop limiter visually only, closest possible but i dont bother much with it. At prints, right after start, during skirt procedure i turn the Z rod by hand, which is easy to do if firmware disables Z motor while not used. Watching the filament being deposited and sort of fine tuning Z during that skirt thingy and sometimes even during first layer. Could see how its deposited, much its squashed, etc

In my experience ABS always stick to kapton tape over aluminum plate heated above 110C at the layer height. So there's really no need to tweak the first layer height around to squash the filament. With unheated blue painter's tape and PLA, I did find that I can't reliably make it stick unless the first layer is closer than the layer height.

Thanks for the insights. I'll look into the Bottom plugin.

Noobman, thats a great idea to unlock the Z stepper while in Skirt. None of my axis are free during any phase of printing... Do you know how to set that up in the firmware?

Steppers motors draw most current when they are stationary, so the Z motor is usually disabled when its not used, so it doesnt consume current and doesnt heat up either. The Z rods have a thread pitch low enough so the friction gets leveraged too, which i think its called autoblock feature or something.

I dunno what firmware you use. If its sprinter look for " //Disables axis when it's not being used." and you will see Z is by default "true". I think old Fived firmware had same just with settings of 1 and 0. Teacup seem to do it automatically, moreover Teacup seems to disable all stepper motors if they arent used for like 30 sec or 1 min or something like that, dunno exact tho. For other firmwares dunno either, but i think in case of Z at least this feature should be fairly common.

Maybe some could say when you turn the rod there are some currents being produced by the motor that go back into the stepper driver. Which is true but depends on the proportion of the effect, i think its fairly neglectable. Also i have stepper drivers which i think can take much more abuse than that. But be gentle with it and dont overdo it, in extremis could be a small chance to get it wrong if abused and turned too fast with a weak stepper driver, dunno what to say exactly about that, but have that in mind.

I use it like that mainly so i dont have to bother with Z endstop too much, and i find things pretty easy this way.

Taken a look at the Bottom profile. Turns out that it was on and Addition Height over Layer Thickness was set to 1.0.

So that's why the first layer was so far from the bed. Cos I gave it some allowance when settle Home Z (0.4-ish maybe?) and with the Bottom setting, it started the first layer much too high.

Thanks for the help!

How about having a circuit running through the tip or metal bed so that when you home Z and the tip touches the bed it stops at 0.0 ?
Thats the only way I can imagine u would get rid of the Z end stop. You would want your firmware to have a very good reaction time though or I'd imagine it would cause alot of problems.

A pin or hard wire hanging through the center of a washer, put a plastic nub on the end and set it just below the nozzle height. When it hits, it completes a circuit by joining the pin and the washer, triggering 'bottom'?

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How about having a circuit running through the tip or metal bed so that when you home Z and the tip touches the bed it stops at 0.0 ?

That's entirely possible. Hook that up to your electronics like an mechanical endstop. Teacup has the SLOW_HOMING flag for this.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

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jason.fisher
A pin or hard wire hanging through the center of a washer, put a plastic nub on the end and set it just below the nozzle height. When it hits, it completes a circuit by joining the pin and the washer, triggering 'bottom'?

If it's below the nozzle, then it would drag on the part being printed. You'd have to retract it after it hits the bed like Nophead did here with a mechanical switch. In fact, what you're describing is a mechanical switch also.

How about making a sandwhich with some sensor like this one in between bed and a plate, then the sensor can sense the height of a probe or the tool itself.

Edited 1 time(s). Last edit at 11/20/2011 05:39AM by NoobMan.