ABS warps because the bottom of the part has cooled and shrunk whilst the top is still hot, and the resulting stress peels the corners off the bed. I knew this in theory for ages. I learned it properly by watching the corners of a perfectly good print curl up like stale bread, three hours in, on a part I needed the next morning. The fix is well understood: keep the whole chamber warm so the layers cool evenly. The fix is also faff, which is why I put it off for months.
PLA had spoiled me. It prints happily in open air, it doesn't much care about draughts, and the bed runs cool. ABS is the opposite of forgiving. Open the window in the next room and the temperature swing is enough to crack a layer bond halfway up a tall part. My printer lives in the garage, which in late September is exactly the wrong place: cold, draughty, and prone to the door being opened by someone fetching the lawnmower at the worst possible moment.
The cheap version first
My first enclosure was a cardboard box. I'm not embarrassed to say it, because it worked well enough to prove the point. Put a box over the printer, trap the heat the bed and hotend are already throwing off, and the chamber climbs ten or fifteen degrees above ambient on its own. The warping eased immediately. It was ugly, it was flammable in a way I tried not to think about, and it was a clear signal that the problem was solvable with nothing more exotic than not letting the heat escape.
The eventually bit
The proper version took longer because I kept overthinking it. I wanted active heating, a thermostat, a fan, the lot. What I actually built, eventually, was far simpler: a frame of aluminium extrusion with acrylic panels, a magnetic door, and crucially a gap at the top because you do not want to cook the stepper motors or the electronics. The bed does the heating. The enclosure just keeps it in. A cheap thermometer probe through a grommet tells me the chamber sits around 40°C once it's been running twenty minutes, which is enough for ABS to behave.
A few things I got wrong before I got them right:
- Sealing it completely. Trapped heat is good, trapped heat around the control board is a recipe for thermal shutdown and a shortened lifespan. Vent the electronics, enclose the print.
- Ignoring the first-layer adhesion separately. The enclosure stops warping mid-print, but the part still has to stick in the first place. A brim and a wipe of the bed with isopropyl did more for the bottom layer than the chamber did.
- Rushing the warm-up. Starting a tall ABS print into a cold chamber undoes the whole point. I let it idle with the bed hot for a bit first, so the air's already warm when the nozzle starts laying plastic.
The result is undramatic, which is the goal. ABS now prints with flat corners and parts that don't crack along a layer line when I flex them. No active heating, no thermostat, no fire-risk cardboard. Just a box that keeps the heat the printer was already making, which is what I should have built the first time instead of the fifth.