I have an ender 3 pro. i have an 8 bit silent board. I installed the cr bl touch device to attempt to help at adhesion issues, possible warped bed. I had new firmware flashed, sensor lights up, a touch pattern is performed when requested, but no matter what I seem to do I can never achieve adhesion anymore. I have attempted with new pla, old pla, no change. My height always seems to be too high. I have tried using babystep to adjust but it just never appears to work. I am one head shaking session from bringing it to a professional somewhere. any suggestions?
Step zero is to make sure the bed is properly cleaned. I know there’s been a few times when I did work on my printer and rested my arms on the bed without thinking about it, then wondered why plastic wouldn’t stick. It’s surprisingly easy to overlook. Also doublecheck the bed temp settings in your slicer - I tried a new filament once and was all “why won’t this work” until I reallised that the bed temp was set to 58 for the first two layers and then 0 after that, so after about 20 minutes it cooled off enough to release the print.
If you’re confident there’s no issue with the bed itself, it’s time to check your tramming. Here’s what I ended up doing with my Ender-5:
First, retract the BLTouch’s probe, and then manually lower the nozzle until it’s actually touching the bed. Go slow so you don’t damage anything, but keep going until you can’t get a thin piece of paper between the nozzle and the bed any more. That is very close to being your zed’s actual zero. (It’s probably not 100% because we’re talking about fractions of a mm, but it’s really close.)
If the printer also thinks the zed height is close to zero, then hooray! There’s one possible problem eliminated. If the printer doesn’t think the zed is close to zero, then… I honestly don’t know how to fix that. It didn’t happen to me. But at least you’ll have narrowed down the issue.
Anyway, now back off Zed to 15mm or so, just to have room. Then deploy the BLTouch probe and slowly, slowly, bring the zed down until the probe contacts the bed. Once you’re close use the smallest increment the firmware allows. You’ll know the probe touches when the LED in the BLTouch changes colour.
Note what zed height the printer is displaying. This is, nominally, your zed offset. Remember that zed offset is a negative number for a BLTouch.
Next, repeat this process all over the bed. Take note of your X and Y positions and draw yourself a grid. Record the zed position that trips the probe. Basically, manually determine the bed mesh and write it down so you can actually see what it looks like.
If the various zed heights are all close to each other, then your bed is trammed reasonably well. Closer is better, but anything under a mm should be good enough. If you see that one size is much higher than the other, you want to manually adjust the tramming.
Once the bed is decently trammed, use the zed offset you determined using the probe, and see what happens. If the nozzle is so high plastic just won’t stick, adjust the zed offset until it does.
Remember that the larger the absolute value, the closer the nozzle gets to the bed. Or, the more negative the number, the closer the nozzle gets to the bed. Thus, a zed offset of -4 is closer than -3.
The only other advice I have is sometimes the offset is greater than you think. I had to replace my probe at one point and the new one was a different length, meaning I ended up changing the offset by over 2mm! So if you’re too far away from the bed, just keep tweaking the offset until you finally make contact.
Anyway, I’m not the most experienced printor here, but that’s what I ended up doing. It’s still not perfect but it got my printer working well enough.
@VagabondElf has good information there. Check the bed to be certain it is flat. If it is warped a BL will not completely correct the issue. Ant labs suggests the ideal range for correction is less than the nozzle diameter up or down. That is a small amount. The bed needs to be good and the BL is a polish more than a correction.
Sometimes on the lower end printers the parts are just bad, and fighting to make it work does not solve the issue the easiest is to just replace it.
My last printer I bought (4 of 4) had exactly the issue you are having. I too put a BL on it and it still failed constantly. I spoke to ant labs at length and discovered the bed was beyond the probes abilities to adjust. I ended up replacing the bed 4 times to get a good (ok not great) one. It is now consistent and adhesion is no issue at all, now.