I have made some parts, AS well AS downloaded from Thingiverse.
When I print them out, They does not fit.
I have printed a box with a lid, but the inside of the box is a litle bit to fit the lid.
Is there any way to calibrate this?
print a test cube of known size, measure it and and scale the object accordingly. Also look at the box you printed, measure it and scale it down or the lid up a little.
Also look at the model you downloaded. If there is absolutely no clearance included, it will never fit without scaling or grinding it down afterwards.