First Layer Printing Unevenly with BLTouch

#1
Hey guys,
I have the Gmax 1.5+ and it comes with the BLTouch sensor. I've been having a problem printing when it comes to one of the corners. The calibration process seems to be perfect with the touch sensor checking 9 spots on the bed and everything ,other than the corner, is printing perfectly. When it reaches the bottom right corner, it appears that the bed bends upwards and so the extruder comes too close to the bed. I thought maybe the problem was from the clips holding the heated bed so I swapped the clips but nothing changed. Then, I also thought that maybe if I adjust the height of the touch sensor, I could get the extruder to print perfectly on that higher corner and the extruder be slightly too high, but functional, on the other corners. This didn't work as the the extruder on the other corners were too high. So I was wondering if maybe there was a way that the touch sensor could read the difference in height in that corner and adjust the z-axis when it get closer to that corner.
Here is what the first layer prints looked like: (I pushed down on the bed which is why the skirt is the only one affected and not the actual print is not)
https://drive.google.com/file/d/0B-sr-y ... sp=sharing

Thanks for reading this far and all solutions and tips would be greatly appreciated!
 
#2
That is certainly possible, because if the corner turns up AFTER the probe area of the bL touch it wont register it as higher than the surrounding areas.
I find that the only way the BLTouch is good enough to overcome the fact that it is having to overcome what is almost certainly a not truly flat glass surface is by raising the first layer height to 150% or 200% and then you will see slightly smooshed layers in that corner of yours, and slightly thicker layers in the rest of it.
 
#3
Thanks for the reply and the suggestion. Strangely my first layer height is already at 300% as that was the default first layer height in Gmax's config files. However, I don't see the reason for why my bed would be raised AFTER the BLTouch sensor calibrates the bed. I'm thinking about using some paper to make up for the height difference during calibration but I would like a more precise, reliable option than a few pieces of paper
 
#4
There are two ways to change the height... the screws on the BL touch, or in the firmware..
I would always just print the first layer of a small box in the middle... if it needed raising, id unscrew the bl a quarter turn per side and try again.
Its worth it when you get it done right.. quality is insane :)
 
#5
I've successfully printed a small calibration cube and it came out wonderfully. It's with big prints that extend to near the ends of the bed which gives me problems, changing overall z-axis won't help it sadly but thanks for the suggestion.
 
#6
do you have the heated bed? if you do, then im not sure because that glass is VERY good, compared to the stock glass.
The stock glass that I had was awful. had pits and valleys all over the place.
 
#7
Yes, I do have a heated bed but I seemed to have solved the problem by putting 6 sheets of paper and folding it and laying it out for touch sensor during calibration. However I'm getting a new problem which is the wavy first layer where the filament isn't sticking to the bed so I'm not sure how good my method really is but the skirts are coming out beautifully now.
 
#8
If its not sticking to the bed it could be a few things. Your printer head is not the optimal height above the bed. If it is than increase your temperature and/or slow your first layer speed down to increase adhesion.