Setting Z end point - driving me nuts

I have learned the importance of the establishing the zero point for Z axis. Right now it's the single most critical factor deciding the print out come for me.

When it's set too high (too much gap between the heated plate and the hot end tip) the lower layers (not just the first layer, but several of them rather) curl up and mess up the shape.

I can see the continuation of this effect in the higher layer, but it gets progressively less severe and if the shape is tall enough then I don't see it in the upper layer. I think I may actually use this into my advantage with certain type of shapes - like the end cap for shower curtain rod that I printed the other day. This "rounded" end would've been ideal, but of course that was one of the few prints that came out crisp. lol

When it's too low then the hot end digs into the below layer and the whole thing become so messy in no time.


Okay, so I spent quite some time to set the zero point for Z axis, and figured out the ideal first layer thickness. However... unfortunately, for whatever reason, the gap between the hot end and the heated plate changes ever so slightly between EVERY print!!

I adjust the screw to re-establish the correct end point. If I'm lucky I get it right.. if I am not so lucky (which is the case a lot of times) then it's set either too high or too low... I have to stop printing after a few layers (so I have to be watching it - I can't start printing and leave), scrape it the mess off the glass plate, try to recalibrate the z zero, and restart... over and over until I get it right.


Is something wrong with my printer? Did anyone ever had a difficulty setting up the Z end point and keeping it? Or, is there some trick that would allow me to have some margin of error with this setting?

I have the same problem with my prusa.

A simple solution that insures that the distance is always correct....

I use Ponterface and have created a "Z=0" Button.

1: Preheat the heated bed and extruder and position the extruder
in the center of the heated bed .

2: Home the Z axis on a slip of paper and adjust up or down as required using the Z 0.1 + / -,

3: When the height is satisfactory use the Z=0 button.

Check slicer and insure that your beginning Gcode does not include a "home XYZ",
if so change it to just "home X and Y". Do,this proceedure everytime the heated bed
and extruder are allowed to cool.

to be honest i would try to heat the hotend and the heatbed to nearly the temp and do each corner meaning each corner diagonal to each other, you have to allow for expansion due to the heat for instance on a cold bed and hot end be perfect fit once its to temp the espansion makes the gap smaller

Edited 2 time(s). Last edit at 07/29/2013 03:44PM by chris33.

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up and running
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Wow.. that's a neat trick, but... You have created a Z=0 button? What do you mean by that? I used Pronterface, too, but there's no such button. Could you kindly tell me how to get this Z=0 button thing set up?

Thank you.

bigkahuna Wrote:
-------------------------------------------------------
> I have the same problem with my prusa.
>
> A simple solution that insures that the distance
> is always correct....
>
> I use Ponterface and have created a "Z=0" Button.
>
>
> 1: Preheat the heated bed and extruder and
> position the extruder
> in the center of the heated bed .
>
> 2: Home the Z axis on a slip of paper and adjust
> up or down as required using the Z 0.1 + / -,
>
> 3: When the height is satisfactory use the Z=0
> button.
>
> Check slicer and insure that your beginning Gcode
> does not include a "home XYZ",
> if so change it to just "home X and Y". Do,this
> proceedure everytime the heated bed
> and extruder are allowed to cool.

Hmm.. I haven't really thought about this heat expansion thing... Yeah, after seeing both you and bigkahuna mentioning about heating up the hot ends first, now it make sense.

Thanks!

chris33 Wrote:
-------------------------------------------------------
> to be honest i would try to heat the hotend and
> the heatbed to nearly the temp and do each corner
> meaning each corner diagonal to each other, you
> have to allow for expansion due to the heat for
> instance on a cold bed and hot end be perfect fit
> once its to temp the espansion makes the gap
> smaller

yamster in pronterface theres a + button next to graph click that give button name ie Z home put in G28 Z0 and then save

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Check my rubbish blog for my prusa i3

up and running
[3dimetech.blogspot.co.uk]

I had been wondering how to deal with different thicknesses of glass in one printer, now thanks to you guys I think there is a way. Thanks!

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Yvan

Singularity Machine

Thank you!

By the way, I think the command is G92 Z0, not G28 Z0.

G28 it is

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Check my rubbish blog for my prusa i3

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But G28 is to home all the axis, using the end point switch, which is not what I want to do.

What I want/need to do is (per bigkahuna's suggestion) to place the hot end bottom at the exact distance away from the heated plate (using the Z 0.1 +/- control), and establish that as the z axis zero - regardless of the state of z end stop switch.

If I send in G28 at that point, it will simply try to re-establish the z axis zero one more time, using the end point switch, basically canceling what I just did.

Isn't that right?

"G28" homes X, Y and Z

"G28 X Y" will home only X and Y

not if you G28 Z0 if i put Z28 on its own

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Check my rubbish blog for my prusa i3

up and running
[3dimetech.blogspot.co.uk]