Nothing beats waking up in the morning after a 10 hour night print and finding a huge blob of molten plastic where your part should be. (Ultimaker, and probably due miss-aligned bed - again.)
Note to all printer and kit manufactures, present and future : I am never buying a wood frame printer. Ever.
Hate to tell you this but this could happen to any DIY printer - plywood or not. What happened? How’s the bed to blame?
Plywood distorts with changes in temperature and humidity. As it ages, the rate of distortion increases. Every time you tighten a screw, it eats a bit into the wood. Eventually you’ll be facing a losing battle as everything goes out of whack.
In this case, the bed holder has twisted a bit, lowering one corner a 1 or 2 mm. This is enough that the first layer doesn’t attached to the bed, and ruining the entire print.
You left it running overnight without at least watching to make sure the first layer worked? O:
I knew you would ask that 
Yes, I checked that the first layer worked. But I didn’t wait until ALL the first layer was printed, because it was a large platter of parts and the first layer takes forever.
Ive heard the moisture argument before but dont believe it. All structural components have their drawbacks… even metal will flex and a printer with printed parts has just as many problems. Unless you go industrial, there is no way to avoid a certain amount of flex regardless of frame material. You have to be able work with that regardless of your machine.
My sealed and painted plywood frame is working without a hiccup for me. That being said, I made my bed carriage from FR4 since plywood would definitely warp over time when being heated like that, even if it was properly sealed.
A huge problem with wood is creep (slow, permanent deformation) which occurs when the strains on the wood reach a certain level for extended periods of time.
Even the best quality plywood warps over time. It’s just the nature of wood. Doesn’t matter how long you dry it or how you treat it. Aside from a printer obsession I make furniture (a lot of which uses ply) and any good cabinet maker knows to design to accommodate for some warping. I would be surprised if Ultimaker et al have found a way to mitigate this issue. In fact, perhaps it’s why they’ve been so reticent in adding a heated bed; heating/cooling the bed (and thus the frame) repeatedly would likely exacerbate any warping over time. Anyhow, can it be fixed? Would it be possible to replace the warped part or plug and re-drill a loose hole? I suspect Ultimaker would come through with replacement parts, ply isnt exactly expensive in the volumes they must get through and they have a good rep when it comes to support (from what I’ve heard).
Look, I teach woodworking at the university and I get the whole wood/moisture/warping issue and the material is not the greatest for creating a machine tool, I just dont think its a significant concern with DIY 3d printers. At least not when compared to the design of the machine. Design is much more important than the material. Look at the Soliddoodle - it uses welded steel but that doesnt make it a fantastic printer because the design of the machine falls short - albeit intentionally to reach a low price point. The MakerBot Cupcake wasnt a terrible machine because it used ply it was terrible because of many other mechanical issues inherent in the design. Its not like we are making a machine to mill engine blocks here… a DIY 3d printer is still a glorified robot hot glue gun.
I think it could happen to all. I was cooking and I decided to start a small print in the meantime so that it could be finished when I would come back. I looked at the first and second layer and then a run away in the kitchen to avoid burning food. When I come back 20 minutes later there was a big blob, since probably the two layers should have suddenly detached from the kampton (heated) seconds later I went away (!!!) creating a big mass of plastic around the head instead of the object…
I’m with @Brian_Evans on this one. Warping really isn’t as much of an issue as people make out…
I have one of the very first Ultimakers and it’s never really needed the bolts to be tightened up and I’ve never see any signs of the plywood warping. I re-level the bed, sometimes on the fly as it’s doing the first layer, every month or so and it’s happy…
Hey @Dave_Durant , how is your Ultimaker holding up after what two years? Have you upgraded to the new rev2 hotend? Still reliable and decent prints?
It’s fine - printing right now, actually. I’ve done a few upgrades: steppers (which got hot but still worked fine;.new ones don’t get hot), the new hot end and the filament drive.
After reading this thread tonight, I realized that I’d never gone back and tightened up the frame so I poked a dozen at random. They’re all still nice and tight…
Being a regular wooden Replicator (and a ThingOMatic prior to that) operator, I can say that after recalibrating for any configuration changes, the printer is very repeatable - the trick is to keep its environment steady and preheat your machine so that it is at equilibrium before you start your job.