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curved bed?

Posted by ThierryT 
curved bed?
April 30, 2013 02:11PM
After some issue with my Z-rod, I've had to level my bed again
and, so, got this very irritating move up and down between bottom left and right corners.
there's no way i can have indicator to stay "even" (sorry for poor english) between corners, even when they're leveled
always going down until I reach middle (lowest point) and then going up again.

video below if not clear

vid of indicator while leveling bed

So, I guess my bed in curved?
what can I do to correct this??
should I better not care???
Re: curved bed?
April 30, 2013 02:17PM
Do you have the piece of glass on the heat bed, or is the dial gauge measuring the heat bed itself?

You should have the glass in place during the bed leveling steps.

Re: curved bed?
April 30, 2013 03:25PM
If you do have glass on it, what happens if you turn it upside down

Re: curved bed?
May 01, 2013 09:07AM
yep, leveling with glass on

upside down: change nothing... indicator moves same way (anticlockwise until middle, clockwise after)

and that puzzles me. Guess my bed is not curved as it moves same way? at least glass is not curved

so I tried to see what impact clips have (ok, my girl did). And this "curved effect" mostly disappear when I remove clips. Bed is then unleveled (a bit) but "curve" comes back when I lvl it without clips.

Turned glass 90°. Leveled it again. Got a very small "curve" after lvl (at least on bottom of bed, did not yet try lvling front)

(lvling while posting) curve is indeed in both axis. A bit more on Y than X.

Try without glass. amplitude is now crazy. leveled (at least, the best I could with that annoying "curve"), indicator moves +/5 graduations on X (so, "middle" is 0.05mm under corners, I guess). A bit more on Y axis (say +/-10ish). With no glass, (bed not leveled) "curve" is 20-25 on X, 25-30 on Y. And center of bed is -80 graduation compared to corners (.8mm???)

glass on again. prolly not previous way as not leveled any more. But, whatever, center of bed is 10 graduations below corners (more or less, not lvled).

is that 50-100 microns (I think, lol) acceptable between centre and corners?
this is so frustrating, thinking to wiring another bed etc...
Re: curved bed?
May 01, 2013 09:46AM
I wonder if the spring in the gauge is strong enough to bend the glass sheet in the middle. You could extrude a line across the bed and see if it really does vary that much in thickness.

Sorli mirror tiles from Ikea work well and they are 3mm thick so a lot stiffer.

Re: curved bed?
May 01, 2013 09:47AM
best I could level, indicator shows:

56 49 56

51 51 49

56 51 56

is this acceptable? anything I could do?
Re: curved bed?
May 01, 2013 12:22PM
Probably a stupid question, but are you sure the rods are also straight. Did they roll on a flat surface?
Re: curved bed?
May 01, 2013 01:22PM
They are precision hardened ground rods so they should be straight.

Anonymous User
Re: curved bed?
May 01, 2013 05:08PM
on my printer its same. i think your bed is leveled fine.
0.05 is almost nothing.
Re: curved bed?
May 04, 2013 08:42AM
rods are fine, no issue there

so, printed some tests with [www.thingiverse.com]
and got no sign of "curve effect" on printed test, center part is same exact depth despite bed being 50 microns lower than corners...
Re: curved bed?
May 04, 2013 08:50AM
So perhaps it only appears lower because the spring in the dial gauge deflects it.

Have you tried laying a straight edge across the diagonal to see if there is a gap in the middle?

Re: curved bed?
May 08, 2013 07:44AM
test I used has diagonals and noticed no difference between corners and center (nothing significant on average at least)
Re: curved bed?
May 08, 2013 07:46AM
So I think the gauge bends the glass so the reading in the middle is false. It doesn't matter because for levelling you only need to measure at the corners.

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