Print bed Leveling

OK so I spent 2 hours last night finally getting my bed leveled on my prusa - I printed out a few pieces (Test Cubes, Z Endstop Adjuster, Some XL gears) So everything was great last night. This morning I get up and went to print Z rod constraints and my bed is completely un-level again!! This is driving me nuts... If it was just the overall height I could adjust it easy, however the whole dang bed is out, almost like my wood is warping....
I have 1/4 MDF for both the Thin and thick sheets. Is this my problem? Should I go to HomeDepot and get some lexan?

Thanks, Devon

Yes MDF is no good under a heated bed as the heat warps it. Dibond is the best material in my experience.

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[www.hydraraptor.blogspot.com]

Put some corrugated cardboard under the heated bed to insulate. Two sheets of quarter-inch foam board is even better. I have a video that cover this a bit. Look around 1:50

[youtu.be]

I do not have a heated bed, I am printing on masking tape directly on top of the MDF

I think i will go and get some plexiglass today and see if that helps
Side note: Can you print ABS right on to plexiglass?

I have printed at least 20 sets of Prusa parts on a heated bed with MDF sub bed no problems, I use 9mm MDF

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Experimenting in 3D in New Zealand

I think it depends largely on the quality of MDF (what type of glue is used) and the ambient humidity.

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@djamwolfe i was printing on plexiglass and it does not stick very well. the ABS edges peal up, but if you cover it in paint tape and a thin coat of super glue ABS will stick grate! i dont know why but ABS loves old dry super glue. also plexiglass warps after time. i now have a piece of real glass so that it doesnt warp and it works grate. so the best cold bed is some thing hard that doesnt flex with tape and super glue if printing with ABS

Trust me, and every other person on these forums who has come before you. Don't try to print ABS on anything other than a heated bed. Put glass on top, even better. Plexiglass will also warp. Though not as severly as MDF.

The MDF is extremely suceptible to warping caused by heat and moisture.

Thanks for the advice everyone! I will be ordering a heatbed later this week, and getting a piece of glass for on top. I thought I got PLA when I ordered my plastic but when it arrived I noticed my mistake.