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created 12/12/17 - updated 20/12/17

Shop-made 'Third Hand'

I decided to put into action something that I had planned to do for a long time. From my late father’s estate I inherited a cast-iron foot that presumably belonged to some kind of chemical laboratory equipment. Not being impressed with the commercial ‘third-hands’, I kept this piece of cast-iron with the view of converting it into a tool with less and better controllable degrees of freedom. Also just having a pair of cheaply made alligator clamps didn’t add to the useability of the commercial tool that, in consequence, spent most of its life on the shelf. I also inhereted a good quantity of pre-war quality alligator clamps.
The cast-iron foot was de-rusted and a proper seat for the bar-clamp had to be filed – I could not find a way to clamp the piece to the table of my milling machine. The foot then was primed and spray-painted in my favourite ‘bottle green’ (RAL 6007).
Working predominantly on small-scale ship-models with tiny parts, I sized the tool appropriately. The main bar is 6 mm steel and the two pillars are 10 mm aluminium. I actually prefer steel, but in this case working with aluminium was faster on my small machines. The arbors for all the clamps are 4 mm steel rod. The diameter of 4 mm was chosen, as the alligator-clamps have sleeves that are meant to be pushed over 4 mm-banana-plugs.
Thinking about the likely kind of applications, I made a pair of small sprung clamps from steel, a pair of larger toolmaker-style clamps (excellent idea by Michael, btw) in aluminium to be used for soldering, a pair of small hooks in 0.5 mm piano-wire for rigging tasks, and a pair of collect-chucks. 
The collet-chucks are commercial products from China with ten collets that clamp from just over 0 to 3.2 mm. I thought this might be a good idea for clamping wires and perhaps ropes safely without distortion or marring. They were so cheap at 2.50€ for a chuck with ten collets that there was no point to make them myself.
I also plan to make set of clamps from bakelite for soldering, but have not received the ordered material yet.
The thumb-screws are also bought in, as I have local source here in Paris that sells them for one Euro a piece, which is not exactly cheap, but good value considering how much time I would have spent making them myself.

Rather than bakelite (which is phenolic resin filled with wood flour and which is essentially isotropic) I received ‘Novotext’ rods. Novotext is a composite of phenolic resin and cotton fabric. This is bad and good news. The bad news is that its temperature resistance is lower than that of bakelite and, hence, the clamps cannot be used for soldering as originally envisaged. The good news is that Novotext is much less brittle and more elastic than bakelite because the cotton fabric takes up the strain, as does the steel in re-enforced concrete. The material mill and turns well, and you can cut threads in it. So the design is the same as that for the metal clamps. In the end I got some nice clamps out of it, nicer than the wooden ones I attempted.

With small hooks for
rigging work
With small clamps
in steel
alligator clamps
With toolmakers-style
clamps in aluminium
With collet-chucks
to hold wires etc.
  Novotext clamps

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