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After about 150 hours on my printer, I noticed that it started getting out of alignment about every other print. I checked the belts, and all the teeth look good, but the belt had stretched a bit. A two minute job fixed them, and I spent another few minutes making sure I was still calibrated. I think I made one .2 mm adjustment. Now I'm printing as good as new. I check the nut on the top of my hotend before each print. I have it tight, so it hasn't been a problem for a good bit. What else should I check, if anything?

Check the Cheapskate assemblies to make sure they're still tight.

I'm surprised you stretched a belt - they've got cord cores to them.

g.

I've had my Rostock on its side in the back seat of the car about a dozen times. I've noticed that one or two of the countersunk screws in the base have some flex when picking up the machine. This could just be because I was scared of over-tightening things and smashing the melamine, but I would recommend taking off the heated-bed and re-torquing all of the screws in the base.

Wouldn't be a bad idea to re-torque the belt drive pulleys, aluminum t-nuts, motor mounts, and top clamp. Anything you can do to make sure that your geometry is solid, you know?