clarification on Z offset?

ok, finaly learned to tolerate the bed levaling endless cycle of screw a little bit..then the other then the other lol! sheesh. i will be setting up bed levaling for a try (on the smoothie board)

but to the question.

what figure actualy goes into the Zoffset box?

the way i'm seeing it is it, the bounse minous the gap?
e.g. 1mm bounce off of the end stop trigger and a 0.3 gap giving 1-0.3=0.7.......0.7 being the actual height above the bed to the nozzle tip. (then of course detract which ever to get better bed addition etc etc)

have i got it right?


is there a firm ware setting in the config or is it purely the end stop point is the zero height for the g code height?

Edited 1 time(s). Last edit at 10/16/2015 11:32AM by munchit1.

oh yawn... ok i'll wade through google for 4 days, wadeing through the endless shite...useless.

Depends on the printer but you want a 0.1mm gap between the nozzle and the bed. So assuming a level bed, home all axes, move to bed center and assuming your z endstop is set to give you some clearance between bed and nozzle, stick a feeler gauge under the nozzle note the actual clearance then work out the offset to give 0.1mm when you print.

Or home all, move to bed center then send G z10 then use the manual controls to lower the z height gradually until you just can just grip a piece of paper between nozzle and bed, note your z height on the printer's display lets say the printer/host is showing z=0.3mm when you know its actually +0.1mm from the bed then your offset is -0.2mm. Print something if it doesnt stick at all and the filament comes out round change the offset to lower the z height by 0.05mm, if its too squashed or the nozzle is grinding on the bed do the opposite. If you hit the z endstop before you get to 0.1mm and the z axis wint go any lower then in marlin configration_adv.h change "use endstops for homing only" or similar to enable, this will allow you to go lower than z=0, but with a mechanical endstop you can only go a few mm lower without breaking or moving your endstop this is a good reason not to use a mechanical z-min endstop and instead use a z probe/sensor.

As for manual bed levelling its a load of faff, assuming your bed is actually flat, get a z probe of some sort and implement autolevelling/compensation it'll save you hours of messing about.

With marlin autolevelling you can set the z probe offset, or you can just set it in slic3r or whichever you're using and make a note of the setting that works best for you.

Edited 2 time(s). Last edit at 10/16/2015 07:33PM by DjDemonD.

thank you demond, i have a sensor waiting for the resitors.

There was a good post about sensors (http://forums.reprap.org/read.php?1,547498,568423#msg-568423) if you use a normally open sensor then resistors aren't needed as the output pulls to ground so you can connect the + and - of the sensor to +12v and 0v/ground and the signal to the z-min endstop signal pin. It won't damage your board as it grounds the pin when triggered, enable pullup resistor for z min endstop. Check before connecting the sensor by measuring the voltage change when you bring some metal (or whatever depending on the sensor) near to it. It should read some small voltage when open then 0v when triggered. If you want a normally closed sensor (which is much better from a fail safe/avoiding head crashes point of view) then you might be best to use a voltage regulator to reduce the voltage on the signal output from the sensor from 12v to 5v rather than resistors. I tried the voltage divider method and it was pretty flaky. In reality I used a normally open inductive-metal sensor (LJ12A3-4-Z/BX) and just ended up connecting it to the +5v, GND and signal pins for z-min endstop and it worked fine, the LED doesn't light up when triggered but it triggers nonetheless and gives a triggered response to an m119.

Once you've got a working z probe then it's just a case of setting up auto levelling by defining the offset from your probe to the nozzle and your probing grid, one tip with probing grid definition is that the values can be negative as well as positive which enables a large enough grid to have 9 point probing.

Edited 2 time(s). Last edit at 10/17/2015 07:31PM by DjDemonD.

I never did understand what the Z offset was all about and now I still don't.

Even if you go to the center and do as you say to trick the z axis into going to 0.1 mm as the zero point, that doesn't address the real possibility that your four corners are not right and you have to adjust them unless you have joined the fervor for auto-leveling. For me, to disable stepper motors after 'going home', and then slide a feeler gauge under the nozzle at the corners while adjusting the height takes about 2 minutes and then I'm good for a week or so of almost constant printing. I check it about once a week.

What is Z offset? I haven't a clue.

It's a setting in Slic3r (perhaps in other slicing programs also but I don't use any others) which just presumably adjusts all the z-coordinates in the Gcode by the value entered. Useful if you change something minor on the printer or notice it is printing a bit too close/far from the bed, you can just re-slice the print job with the offset applied. Its much quicker than re-flashing your firmware.

And yes it seems it might have more practical application with auto-levelling. I have never had a printer with an easily adjustable bed so just setting the bed at the four corners was never an option.

Edited 2 time(s). Last edit at 10/19/2015 11:15AM by DjDemonD.

I included this in all my Gcodes adding, after the G28 this lines:
G1 Z0.00 ;offset z by 0.00 (Z OFFSET)
G92 Z0 ;reset Z to zero
Why?
My bed is well leveled in all 4 points but I use diferrent mirrors (take out one and put another) and every mirror have a very little difference with others.
So I check level in 1 random point and edit Gcode adjusting the Z offset before print.
It's very useful for me.

Now that makes sense! Thanks!

hmm i was thinking about using a votage reg..thank you for that.

alas i cant get the smoothie board to do it...yet.

i've kept the mecanical end stop, as it turns out it was a good job i did, but it always triggers and a M999 is called for, followed by a 30 odd second wait before it'll do anything, uit does save multiple camands in a que and does them all.