Inconsistent Z Height

[Jrjones]

I'm having issues with getting my first layer to stick consistently to the print bed, sometimes it will work fine, other times it takes me 5 tries to start the same print with all the variables the same.

I think its due to the printer not being able to go to the same position consistently. I made a short video with a dial indicator where I homed and travelled to Z0 10 times in a row, homing between each move, and I get a variation from
-0.023 to +0.02 mm

These are the offsets from my set Z0 height

1. +0.018 mm
2. -0.023 mm
3. -0.023 mm
4. -0.005 mm
5. -0.017 mm
6. +0.020 mm
7. +0.019 mm
8. +0.018 mm
9. +0.009 mm
10. +0.013 mm

Is that normal or can I adjust something to make it more repeatable?
Its not really the difference from my set Z0 that concerncs me, it is more that it is not repeatable, if it consistently went +0.02mm above my Z0 height I would be happy because I can adjust for it.

[youtube]http://www.youtube.com/watch?v=xs4IED2IQUU[/youtube]

I found another topic on this but its not quite the same thing I'm experiencing. http://forum.seemecnc.com/viewtopic.php ... ent#p16747

[guanu]

if your readings are in mm as you posted, being +/- 20 microns should be nothing to worry about... with a mechanical switch and step accuracy of the motors being .0125, I'd say you are within tolerance. Typical first layers are usually a .3 layer and that should more than compensate for any variation that small. As you said, you homed each time so I would assume that the combination of the switch and step accuracy is within their tolerance, if you want to test just the motors, you would home, go to z0, and maybe just go to z10 and back to z0 a few times so you dont have to account in the endstop accuracy.

[Jrjones]

Ok, I've been away for a while but I'm still having issues getting a good first layer adhesion when printing outside the center ~50mm radius.

I purchased a digital dial indicator to make it easier to read quickly, and I have the center and the 3 towers calibrated to within 0.01mm of each other.

I am still have inconsistencies with the Z height however.
If I home and go to the center of the bed, I am usually 0.00 or 0.01 on the indicator, sometimes 0.02mm. This would be within the +/- 0.02 mm that Guanu said is nothing to worry about and I'm fine with that.

However if I first home the towers, go to bed center, and then measure at each tower, I sometimes have a difference of 0.09mm or more.
I made a video, the first half is measuring at the bed center and each tower, homing before each measurement, and the second half is homing before measuring at bed center and then measuring at each tower.

[youtube]http://www.youtube.com/watch?v=GJEkZdntdjw[/youtube]

From the second half my measurements are:
Bed center: 0.02mm
Z tower: -0.07mm
Y tower: -0.09mm
X tower: -0.05mm

I get even worse measurements if I measure between the towers, pretty much exactly what is going on in this thread: http://forum.seemecnc.com/viewtopic.php?t=4868
I see there is no solution it yet, since the posted solution (#define CARRIAGE_HORIZONTAL_OFFSET 38.4) is already in my printer settings.

[Jrjones]

I ran the code that is in the "solution" from here: http://seemecnc.com/blogs/news/14684425 ... -perimeter
I measured my carriage offset to be 37.7mm, it was previously set to 38.4mm and I still get the same result, that the bed is lower in between the towers.

[youtube]http://www.youtube.com/watch?v=hjdDZrNKwwY[/youtube]

I measured 169 points from the center out, and when I have a radius larger than 60mm the bed is at least 0.10mm lower in between the towers.
The worst measurements are on the edge, with them being between 0.3 to 0.35mm lower than the center of the bed.

Since the points are pretty much uniformly lower, what can I do to help this? From reading I don't think tower rotation helps with this correct?

I also don't get why I'm getting that the points at the towers is different than when I calibrate them. If I go from home directly in front of a tower it is 0.00 or +/-0.01 mm, but if I go to one of those locations after going to center, it is off by a bit.

[Jrjones]

Any ideas? I want to print some things that are larger than 120mm long but with this problem I find the first layer adhesion pretty much impossible.

[dajay23D]

is ur main concern first layer adhesion? Omit your z height for a min and focus on getting it to stick first. Are u priming long enuf?