I noticed something strange on my A1 Mini quite some time ago. When I load or unload filament, the print head goes to a +Z location that is greater then the designated build volume for the machine, and knocks off the extrusion cover. Does anyone have any insight on what is causing this?
Pic 1: Z travel exceeds build volume
Pic 2: Normal max Z travel
Pic 3: Knocking off the extrusion cover
How is it even possible that the cover is pushed away? There’s a thick, sturdy screw in there that’s missing. When the axle hits it, it stops. Did you unscrew it and forget to put it back in?
Yes, I removed the screw a while back and forgot to put it back.
Are you saying the cap acts as as stop for Z axis travel? That sounds like crazy poor engineering. (I am a control systems engineer).
This is common practice. There are two options. Either you can install a stop switch, or the control system can detect when the motor encounters resistance and therefore a higher current is flowing.
The printer only does this once during calibration and the reference run, not continuously. The advantage of this variant is that you do not need stop switches an every axis, which often wears out and then cause considerable problems (axle moves endlessly towards the end).
So no, this is actually good engineering and has proven itself in 3D printers. Take a look at print farms that have thousands of hours of operation. 
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I am quite surprised. I come from a background where reliance on a simple piece of plastic to stop a process could literally endanger people’s lives. I guess I’m carrying my industry’s safeguards beyond what others would. I hesitated putting the screw back because I assumed it would result in nasty missed steps from the stepper motor.
You can now act smart - or accept that there are systems that apparently exceed your knowledge and very sensitive electronics are integrated. It’s not like the printer is ramming into the cover.
It’s similar to auto bed levelling - when this feature is activated, the printer measures the plate. It gently presses against the plate each time to take a measurement - This works without a switch, but rather by detecting the resistance.
Whatever floats your boat. 
I accept that you are correct. My industry is much more brute force than 3D printing. Thanks for the education.
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A simply piece of plastic is always more reliable than a mechanical end stop switch which will fail.
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