Start by trying out the position of the potentiometer Knob and push button that is more ergonomic for the plastic box to be used in the project

Cut a piece of cardboard with the same dimensions as the top cover.

Use the cardboard to mark the positioning of the holes

Take note of the dimensions

Now make the holes on cardboard and check if the positon of the controls is good or if it needs to be changed for better ergonomy

Then transfer the measurements to the plastic top cover

Now make the hole for the potentiometer. After the hole is done mark the position of the potentiometer tab and make a hole for it.

The potentiometers used are from the 'big old ones', so it was necessary to trim the side edges of the box right under the top cover

After the trimming the pot fits well

Now take out the potentiometer and make the hole for the push button

Now assemble both the potentiometer and the push button and check if both are firmly attached to the top cover by their nuts

Now it's time to trim the potentiometer rod. Insert the knob totally and make a mark on the rod where the knob ends.

Take out the knob and measure the distance

Make a mark with equal distance from the bottom of the rod

Now cut the rod on the new mark