I’m not sure what I could be doing wrong. After using G29 to level the bed the 4 corners & center 1 layer test print from Teaching Tech website are not the same or even close at times. The bed was leveled manually using the post-it note like Dr Vax suggest. Set the z-offset using Dr Vax’s video BTW this is on a Ender 3 v2.
I have checked that the bed plate and X gantry are all tight and moving smoothly. Running Smith3D 4x4 firmware for the E3V2. Have considered interference from the hot end wire and have the tin shielded braid on the way, will be here Tuesday. At times I think I have more issues since adding the BLT. What the heck could I be doing wrong? And yes I have checked that the connections are tight.
I had this problem and also the bltouch would sometimes error out, tired replacing the bltouch, cables, connectors, etc. After a LOT of research I finally found the problem. The hot end wires were causing EMF interference with the bltouch wires. As the hotend moves around the bed the interference would be greater or lesser. This causes the bltouch to be incorrect in its measurements. I found a fix for the problem. I bought this https://www.amazon.com/gp/product/B01HE0PDG4/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1 and installed the bltouch wires inside of it. Then on the end inside the main boards area i soldered a wire to the end of it and connected it to ground (the frame of the printer). This fixed my problem and now the bltouch works accurately and no errors. If you do this make sure to ONLY ground one end.
This may not be your problem but then again it sounds like it is to me.
I do believe its the interference the hotend moves around the bed along with the cables. This causes the interference to be greater or lesser which changes the accuracy of the probe. I tested this before i bought the sleeving by pulling the bltouch cables out and away from the hotend wires then i checked my bed visualizer plug in in octoprint to see what the differences was. There was a big difference between when they were close to the hotend wires and when they weren’t.
I’m inclined to agree with @Larry it’s random it’s hard to pinpoint. My shield will be here Tuesday. I did discover that the coupler on the the Z stepper was loose. Seated it and tightened it up real good. Does it again and Locktite will be used. I use Prusa Slicer and for what ever reason RC2 has been messing with me too. Sliced the same part I was having issues with using Cura 2.8 and it printed fine. Also went back to the basics Smith3D firmware 5x5 slow, put the yellow spring back on and levelled starting from scratch. The part I’m trying to print has supports and I think that is what was messing me up too. I do want to check out the octoprint virtual bed levelling plugin. Be interesting to see the before and after install the sleeve, I did find something interesting when researching my issue. The bottom of the BLT housing is suppose to be 8mm +/-.5mm from the tip of the nozzle. Haven’t measured mine yet. I currently have a 2mm spacer under mine. Don’t think I’ll be making any changes until the sleeve arrives.
@roon4660 I wouldn’t let this scare you from getting a BLT just remember what you read here and learn from it. I think I’ll really like it when I get it all dialed in
Installed and ran the Bed visualizer in Octoprint interesting explains a lot about what I’m seeing
Right now I’m printing the same part I’ve been having issues with using Prusa Slicer with the default settings, before I was changing the support setting to hopefully get the supports to release better. Set them all to the Prusa recommended instead of the one for the Ender 3 live and learn.