Short answer
Most failures come down to four causes: the part lifting off the bed as it cools, layers not bonding properly, overhangs with nothing beneath them, and moisture in the filament. We catch these before parts ship, but knowing them helps you design around them.
Warping: the part lifts at the corners
Plastic shrinks as it cools. The bottom layers are held flat by the build plate while the layers above pull inward as they solidify, and that tension eventually beats the grip on the plate. Corners curl up first, and once a corner lifts the rest usually follows.
Large flat parts are worst affected, because there is more shrinkage acting across a longer span. Sharp corners concentrate the peel force. A generous radius on the bottom outline, or a small chamfer, spreads it and makes a dramatic difference on big parts.
PETG is far better behaved here than ABS, which is one of several reasons we use it, but a 200 mm flat plate is still asking a lot of any material.
Layer separation: it comes apart in sheets
If layers do not fuse properly, the part delaminates — it splits along a layer line under load, or sometimes visibly cracks during printing. The usual causes are the nozzle running slightly cool, a draught cooling the part too aggressively, or printing too fast for the geometry.
Tall, thin parts are most vulnerable because each layer is small and has cooled substantially by the time the nozzle comes back around. Where a part must be tall and thin, printing it alongside a second copy actually helps — the nozzle takes longer to return, so each layer sets more evenly.
Elephant foot: the bottom bulges
The first layer is squashed into the plate deliberately, so it sticks. That squash makes the bottom millimetre very slightly wider than the model. Usually nobody notices, but if the bottom edge has to slot into something with a close fit, that bulge is exactly the tolerance you needed.
The fix is a small chamfer on the bottom edge in your model — half a millimetre at 45 degrees. It gives the squash somewhere to go and the part drops in.
Overhangs and stringing
Plastic cannot be extruded onto nothing. Beyond about 45 degrees from vertical, an overhang needs support material underneath, which is printed and then broken away — leaving a rougher surface where it touched. Under 45 degrees each layer rests on the one below and prints cleanly.
Stringing is the fine whiskers left when the nozzle travels across a gap while still oozing. It is cosmetic, comes off with a heat gun or a quick trim, and is more common with PETG than PLA because PETG is stickier when molten. We clean it off before parts go out.
Wet filament
PETG absorbs moisture from the air. Damp filament pops and hisses as it prints, leaving a rough, weak surface with visible bubbles. It is entirely preventable by storing filament dry and drying it when it has been open a while, and it is the sort of thing a busy print farm skips and a small workshop does not.
What we do about all this
Every part is looked at before it is packed. If it has lifted, split, stringed badly or shows bubbling, it gets reprinted rather than posted. That is why there is a failure allowance built into pricing: it is cheaper for everyone than shipping parts that disappoint.
What this means when you order
If a print fails on our machines, we reprint it — that is our cost, not yours. What we will do is tell you if a design makes failure likely, because a small change now beats three failed attempts.
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