Ingredients to make 20 spool clamps:
One IKEA chopping board, (Legitim). white polyethylene 8mm thick. 24x34cm 80p in UK
Hole saw. 38mm from poundland £1
M6 coach bolts. 4" or 100mm for lyres, kanteles, dulcimers, mandolins, ukes.
(Longer bolts are needed for guitars etc)
20 of these
25 or 30mm washers 40 of these
Wing or butterfly nuts. X 20
I was able to purchase all the metal hardware from my local wilkinson for £2,99 in their self service pick and mix bags
Total cost for 20 clamps £4.79!
(I can't take credit for this, I read about using chopping boards and hole saws in a mandolin making book by Graham Macdonald but this was the first time I got round to trying it)
Use the hole saw in a bench drill to cut out the clamps from the chopping board.
Inset the bolt with a washer and slide on another clamp piece and washer.
Screw on the butterfly nut
They work really well despite the top and bott being loose. The texture of the chopping board also helps.