Looking forward to your advice and observations, Deven.
Here's the promised vertical positioning diagram. (Not drawn to scale.)
First thing to do is solve for Shaft Height with a typical 3/4" wood panel (19.05mm) and a typical metal panel (1.6 mm) since most panels will fall within that range.
3/4" wood panel:
PanelThickness + 15.6mm (handle to panel distance) +ShaftHeight = Shoulder Height
19.05mm + 15.6mm + ShaftHeight = 46mm
ShaftHeight = 11.35mm
Metal panel:
1.6mm + 15.6mm + ShaftHeight = 46mm
ShaftHeight = 28.8mm
The original handle BodyHeight is 35.6mm, so ShaftHeight + ThreadedHeight + TopThickness (the removable cover) have to fit into that vertical space.
Wood panel:
ShaftHeight + ThreadedHeight + TopThickness <= BodyHeight
11.35mm + 9.4mm + TopThickness <= 35.6mm
TopThickness <= 14.85mm -- Lots of wiggle room there.
Metal panel:
28.8mm + 9.4mm + TopThickness <= 35.6mm
TopThickness <= -2.6mm -- Threads are higher than the handle body, needs some 5mm spacers (or larger) between the stick and panel.
Metal panel + 5mm spacers:
23.8mm + 9.4mm + TopThickness <= 35.6mm
TopThickness <= 2.4mm -- Just enough wiggle room for a 2mm top.
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Looks like the handle will work with 6.6mm (metal panel + 5mm spacers) - 19.05mm (3/4" wood) panels and leaves room for a 2mm recess for the top cover.
Next step: Define variable names and trim/organize the code.
Scott
EDIT: Fixed several errors in the metal panel calculations.