Tunnelling in print bases

[RogerV]

I'm having a little issue with tunneling in some of my flat prints. See the attached pic. This is a 40mm ring, 2mm thick, with a .25mm beveled "foot" as suggested by Greg Kourakos. It's printed flat on the build plate with the default Chitubox settings. I'm printing a pair of them at a time. One always has a tunnel in the same position, and the other always has two tunnels 90 degrees apart - one horizontal and one vertical. There's a very thin base layer, the tunnel, and then the piece picks up normally. (I have chipped out the base layer in the pic for clarity.) The build plate side is showing in the pic.

What might cause this? All layers are solid rings in Chitubox.

In addition, the "foot" seems to disappear entirely, as if the first few layers of the print collapse into one. (It's beveled and inset, it should be visibly distinct.) The completed print is only 1.85mm thick, where it should be 2.25mm. I notice this on many prints - the rook model is missing its bottom bevel, support bases come out as thin films, etc.

After reading other posts here, I ran the LCD test and attached a pic of that. Should it show grid lines like this? It also seems a bit blotchy - so I already have a replacement screen on order.

[cliffyk]

A challenge is that the built-in "exposure test" is unsuited to fully testing the LCD as it only "prints" a hollow box--the central portion of the LCD is not tested.

To test the entire LCD remove the platen an vat, and "print" this .stl file. It is a 120 mm x 68 mm x 5 mm block:



That will test the entire LCD shutter--post a photo of what you see..

How old is your printer--or more importantly how many "printing hours" does it have on it. If more than 250 to 300 hours the LCD is likely worn out and needs to be replaced.

[RogerV]

That's the second pic I posted above. It's a picture of the "print" test you recommend, not the built-in exposure test. I saw your previous replies on LCD health, grabbed the file from those and ran the test earlier.

The printer is new. I have maybe 20-30 hours on it at most. It got a little banged up in shipping, but Elegoo support thought it would be fine. My FEP is in good shape as far as I can tell.

The rook model I printed didn't show the tunneling, but did show the same base flattening. It was printed from a different vat though - so different FEP.

After posting I ran a test with increased exposure times (10 and 60) and decreased lift speeds (45 and 50) and I do not see the tunneling in that test, though the print is still 0.25mm thinner than expected. I'm suspecting a bad LCD at this point.

Thanks for your help!

[cliffyk]

I had a replacement LCD (purchased from Elegoo via Amazon) fail after just 11 hours use--Once i notified Elegoo they were great about sending a new one.

Reducing the lift speeds was a good move--the Chitubox defaults are way too fast...

[RogerV]

Reducing the lift speeds was a good move--the Chitubox defaults are way too fast...

I learned a bunch by watching Greg Kourakos (@3dprintingpro) vids on YouTube before I ever ran my first print.