Heated bed deformation

#1

Hi!
(Perplexing fact at the end, so you could possibly save time skipping the long text ;-))

I´ve had a lot of problems with print adhesion in the last time. First, I thougtht it could be because I use the heaters and Nozzles from http://www.3dprintermods.com , so I reinstalled the original heaters and nozzles.
EDIT: It was NOT the nozzles. They work perfectly! Just to make that clear.
While doing this, I modified my scripts in octoprint for the bed-leveling-process (I added two positions at the frontside of the printbed for verification). And that showed me something really weird: The glass was bent down at its corners about 0.4mm! I was pretty sure that the glassbed was absolutely even when i got it.
So, I tried to remove the glass from the black frame, holding it in both hands (glass facing down) and twisting the frame carefully up and down. Finally, the glass came out. once again I tested the flatness with a ruler and… OMG! It is perfectly flat!
So, I thought the frame must have bent the glass, which had a realy tight fit in the frame. I descided to use my mill to give the glass a bit more space in the frame, only touching it at small areas near the corners of the glass.
Damn… the cable was put through the small hole before it was soldered to the heater… So I had to widen up the hole until the connector would fit through it… I took a saw and started to cut the hole bigger… Strange… BROWN chips from a black bed? Might be some brown duroplastic painted black?

AMAZING FACT: The frame of the heated bed is made of MDF (medium density fiberplate), just painted black. During a cupple of prints with 100°C bed temperature, the wood seems to have lost moisture, resulting in shrinking. This however, seemed to bend my glass bed. (Besides, the region where the center magnet is mounted has also bent about 1.5mm to the inside)

So, I´m thinking about modifying the existing heatbed wich fits perfectly to the design of ZIM, or building a whole new heated bed.
What do you think?

#2

I have had my share of problems with the Zeepro heatbed, especially with the bad MDF material. It arrived with one magnet already fallen off and the rest followed soon after.
Thats why I had to build my own connection from heatbed to triangular base.
To reduce the efforts necessary with adhesion problems and bed leveling, I tested a lot and am now using a carbon print plate (1mm thickness).
I glued it on top of the heatbed, heating it up, putting the glue on and laying it face down on a table with heavy objects on top.
With that I was able to reduce the different height problems. I can see in the first layer that there are still different heights throughout the printbed. But its very small, resulting in a more and less squashed first layer line. But I think thats as good as it can get. Of course with different temperatures there will be more or less bending of the whole plate.
But I can notice those only on the outer most regions.
The problem with that method is, that once the carbon plate has to be removed, I guess I have to destroy everything.

We already have a few custom built heatbeds in the forum and even one up for sale from 3dprintermods, or not?
But to have one perfect ready solution would be great for all.

#3

I have the same problem with my heated bed. Mine actually cracked right down the middle when I was getting a part off I’m guessing in part from it being squeezed by the black MDF and in part from the spatula I was using to pry the part off the bed. Now my bed pops up almost 1mm in the middle along the crack once it heats up. I put a polymide film on it which helps some with the bulge but I can only print small parts in the middle. I’m working on making my own heated bed and will post pictures once I get it working.