Re: basic measurement tools
- the twirl marker is fairly common in watchmaker/instrumentmaker toolboxes.
The wobble-stick is also from that field, primitive but effective.
found this after some internet browsing.
if one makes the pivot point like a ball instead of the fork/groove found in link above it gets more versatile as it can be used in other positions.
I usually use the same 210 long with pivot at 10mm from one end for my versions (20:1 ratio).
and the ball is usually a 6mm brass ball that I solder in place and "capture", that is.
I drill a 4.5mm hole in a piece of brass 75x8x10mm, now drill a 6mm hole just deep enough for tip to poke trough (tip moves 8.05mm into 4.5mm hole)
insert rod (ball already soldered in place) short end towards open end of hole and place a 6mm washer with with 5mm hole and a heavy chamfer on the inside and fairly heavy on the outside. this washer needs to be thick enough to stick out slightly (0.2-0.3mm or so) this is held in place by trio of countersunk screws in an equilateral triangle around the edge with holes placed so heads overlap hole by 0.5mm or so.
I have seen a version with only the screw heads holding ball, there are multiple variants about for the basic concept, I have seen spherical ballbearing used as pivot among others.