Adjusting Z zero during printing.

I'm using Repetier Host and CuraSlicer with a Prusa i3.

As the print starts, the nozzle lowers to the bed, and stops lowering when the endstop Z switch activates. Then the skirt starts to be drawn.

At that point, I'd like to be able to move the nozzle up or down a little, in case the endstop isn't accurate, so I get a better adhesion on the first layer.

Can I do that, and if so, how?

My impression is that Gcode commands typed in at the console during the print are appended to the end of the print's Gcodes, so that
doesn't work - am I wrong?

Thanks for any advice!

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Prusa i3 (from Folger Tech) Noob

[www.flickr.com]

Well, maybe, you could click "pause" during the print, then command the z axis down a fraction then click "resume". But...I don't use repetier so don't know if it works on that s/ware

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Waitaki 3D Printer

I tried the Pause, but it seems to be modal, and so I cannot do anything but "Continue"

Best way is to modify your printer so Z uses only one Stepper and Disable Z-hold, then you can adjust your heigh as you want, that especially helps when printing very small and thin layer

Chri

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[chrisu02.wordpress.com] Quadmax Intel Delid Tools

An alternative approach is to adjust your Z level to be exactly accurate and then print without modifying Z at all.
You can do whatever you want (e.g. lower the head until the Z endstop is reached, then adjust Z manually). Once everything is ready start printing with no need to pause during the print.

I'm using pronterface, but I assume the process is similar.

Note that you will need to modify your G-code to not home the Z axis, and instead, reset Z to 0 at the current height.

I'm using slic3r and I just replace this line:
G28 ; home all axes

With the the following two lines:
G28 X0 Y0 ;move X/Y to min endstops
G92 Z0 ;Set Z to zero

Recently I feel my Z endstop is not very accurate (X / Y accuracy is not as important anyway), so I've been using this technique with good results.
Sorry I don't remember where I read about it - probably a thread in this forum about Z accuracy issues.

Quote
Chri
Best way is to modify your printer so Z uses only one Stepper and Disable Z-hold, then you can adjust your heigh as you want, that especially helps when printing very small and thin layer

Chri

I have an original mendel (one z stepper and a belt) so that is exactly what I have the luxery of doing. I always leave my z slightly high and then manually lower it to just the right height while printing the skirt

-Rob A>

Quote
barakori
An alternative approach is to adjust your Z level to be exactly accurate and then print without modifying Z at all.
You can do whatever you want (e.g. lower the head until the Z endstop is reached, then adjust Z manually). Once everything is ready start printing with no need to pause during the print.

I'm using pronterface, but I assume the process is similar.

Note that you will need to modify your G-code to not home the Z axis, and instead, reset Z to 0 at the current height.

I'm using slic3r and I just replace this line:
G28 ; home all axes

With the the following two lines:
G28 X0 Y0 ;move X/Y to min endstops
G92 Z0 ;Set Z to zero

Recently I feel my Z endstop is not very accurate (X / Y accuracy is not as important anyway), so I've been using this technique with good results.
Sorry I don't remember where I read about it - probably a thread in this forum about Z accuracy issues.

This is a great suggestion - thanks! I'll give it a try.

There are options to make the first layer a different height then the following layers. If you feel its not perfectly accurate you can do something like a .1mm first layer then have everything else be .2.