DIY Powercord

Can you use loctite to keep the screws from loosening ?

Loctite or a small lock washer under the head of the screw.

When I assembled the powercord, I screw it to tight.

Cykeric,

I assume you mean tight.... Not to tight and thus stripped?

What type of conductors are used in the cord?

Fine strand stranded?
Solid core?
Parallelled solid core strands?
Effective wire gauge size under each termination?
14, 12, 10, awg?

Other than fine strand stranded any physical movement of the cord at the terminations of the IEC or plug will loosen up.
Not because the screw actually loosens up but rather because the conductor metal under the screw/ and or terminal plate changes form because of the physical movement at the terminals.

About the only thing you can do is re-tighten the terminations and then solder the wires in place.
A good flow of solder to termination will prevent the wires from moving thus prevent deforming the conductor metal.

Only other thing you can do is re-tighten the terminations again and try not to disturb the cable.
Jim

ea48 is correct. The screws are not loosening, the material under them is deforming.
Retightening them is the answer. The alternative is to crimp them
Also after a few tightenings, the material will not deform as much. The gaps get filled.