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 Post subject: A Third Hand
PostPosted: Mon Dec 18, 2017 4:01 am 
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Joined: Wed Sep 28, 2011 12:04 pm
Posts: 854
Location: Paris
Inspired by an excellent example in another forum (https://modelshipworld.com/index.php?/t ... ent-452268 and newer version further down in the thread as well as a review of it: https://modelshipworld.com/index.php?/t ... ent-473797), 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 a some sort of chemical laboratory equipment. Not being impressed with the commercial ‘third-hand’ 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 that tool that, in consequence, spent most of its life on the shelf. I also inhereted a good quantity of pre-war quality alligator clamps.

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Third hand with small hooks for rigging work

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 painted in my favourite ‘bottle green’ (RAL 6007).

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Third hand with small clamps in steel

Working predominantly in small scales 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.

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Third hand with alligator clamps

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.

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Third hand with toolmakers-style clamps in aluminium

The collet-chucks are a commercial products from China with ten collets that clamp from 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 1.50€ for a chuck with ten collets that there was no point in makimng them myself.

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Third hand with collet chucks to hold wires etc.

I also plan to make set of clamps from bakelite for soldering, but have not received the 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.

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 Post subject: Re: A Third Hand
PostPosted: Mon Dec 18, 2017 4:39 pm 
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Joined: Sun Aug 20, 2017 9:46 am
Posts: 419
Probably make a good jig when making multiple aeriels - the kind suspended from circular or star shaped separators.
:wave_1:


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 Post subject: Re: A Third Hand
PostPosted: Wed Dec 20, 2017 5:35 pm 
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Joined: Wed Sep 28, 2011 12:04 pm
Posts: 854
Location: Paris
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.

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Third hand with made from ‘Novotext’.

Some people asked me about the construction details and below you find an ‘exploded diagram’ of the tool.

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Third hand ‘exploded’

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 Post subject: Re: A Third Hand
PostPosted: Wed Dec 20, 2017 7:36 pm 
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Joined: Sun Mar 18, 2012 12:31 pm
Posts: 117
beautiful craftsmanship wefalck!
envy your talent for machining and the tool you have!


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 Post subject: Re: A Third Hand
PostPosted: Wed Dec 20, 2017 7:39 pm 
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Joined: Tue Jan 11, 2005 1:40 pm
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Location: In the hills of North Jersey
Wow. That is damned impressive.

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 Post subject: Re: A Third Hand
PostPosted: Sat Jan 13, 2018 6:49 pm 
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Joined: Mon Jan 10, 2005 5:30 pm
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Location: Nr Southampton England
...........when the means to the end becomes ..............a whole new hobby....

most impressive !

:thumbs_up_1: :thumbs_up_1: :thumbs_up_1:

Jim B

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 Post subject: Re: A Third Hand
PostPosted: Sun Jan 14, 2018 3:48 am 
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Joined: Wed Feb 09, 2005 5:45 pm
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Location: Abu Dhabi
Man I am jealous ,what a great tool You made :thumbs_up_1: I only can dream in one like yours :wave_1:

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