weighing cradle

I have a food scale, and I thought I could use it to weigh my filament rolls. After a little designing, I came up with this model. It's wide enough to hold most spools, plus it has a lip in the back to keep the spool on the cradle.
I have noticed there is a variance in the empty weight for some brands of spools which makes it hard to assign a set empty weight. Also, some spools have more than the advertised weight on them. So, a 1 kg spool might have 20 grams extra, sometimes.
UPDATE: I added the step file for the weighing cradle.