Welcome to the SeeMeCNC Community

We watched the Steve's Extruder Head build video. Pretty fun!

In the video, Steve walked away for a bit to get a 11mm socket to press the bearing in. (Either that or he had a quick beer break and the socket was just out of view.)

My wife (in Quality at a major aircraft engine manufacturer) asked whether or not it would be better to use a blow-dryer to heat the gears up a little before pressing the bearing in.

This might do two things:
Avoid accidents, warpage and dents
As the part cools, it might be better seated

Question - before assembly:
Would gentle heating help or hurt?

I wouldn't , It could warp the gear. You should have no problems pressing the gears in with a vice.ABS expands enough to not crack.

I wouldn't worry too much about heating the gears slightly. They are actually made from acetal, so they soften with heat easily, just make sure that its flat as it cools

What about the opposite, freeze the bearing. Would that be bad for the lube? - Old techie trick freeze a noisy clicking harddrive to get data off it.