Lead Weight – First Attempt at Casting

There are a pair of cam followers on the Colonel Rutherford model, one moves his head, the other his writing hand. The Colonel’s head has plenty of weight so it falls back into place on its own but the hand needs extra assistance to move back after the cam has released it.

A cam works in one direction only, the cam will push the cam follower up but something else is needed to pull it back down. I could use springs but I’ve decided to use weights in this model. I’ve collected loads of bits of lead over the years, mainly from wheel balancing weights found on the side of the road. My plan is try melting and casting the lead to form usable weights.

I used brass wire to create a hanger for the top of the weight.lead-a05

 

I then packed a tin can with white sand from the local builder’s merchants and made a hole in the centre with a 20mm dowel.lead-a06I pushed the wire into the bottom of the hole so the the arch of the loop was buried in the sand.lead-a07

I melted lead in a pan in the kitchen (#truelove was out) then #1son captured the moment I poured the molten lead into the mould.lead-a01After cooling for a few minutes I knocked out the sand…lead-a02…then washed off weight to complete.

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lead-a01I’ll probably try again to see if I can make a smoother finish to the weight but it certainly works well as is.
Total weight for this version 240g.

Any tips on smoother casting would be welcomed!

 

 

 

 

 

Laser Cut Wooden Chain and Sprocket

chain-a12The first version of the Colonel Rutherford model used a chain drive to transfer the drive from the motor to a gear rotating an airmail aeroplane above the model. I originally used a plastic snap-together chain that I bought from eBay. It worked well enough but some of the links were a little stiff giving the motion an uneasy, jerky look. Visuals are as important as how well the models work in these automata so I set about making an improved chain drive, this time using laser-cut wood. Here’s a rig showing the end result in action

chain-a01I cut out lots of little pieces on the laser cutter to construct the chain. For simplicity each link of the chain is constructed from four identical pieces.

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Two of these pieces are glued together for each side of each link. A cocktail stick through the small holes is used to ensure everything is lined up properly then the pieces are clamped up and left to dry .

chain-a03Lots of links are needed!

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The cross pieces of the chain are made from 10mm lengths of  9mm dowel. I drilled the dowel through the centre making a pilot hole for the screws. The screws are fitted using appropriate washers and tightened just enough so that the links are flexible.chain-a06

The sprockets are made from three layers of 3mm ply glued together.I sanded the side of the sprockets off to help guide them into the centre of the chain.chain-a07

Here’s one of the finished sprockets showing the tapered teeth.chain-a08

This version of the chain drive is a test bed to ensure that it works properly. I’ve mounted the two sprockets onto an MDF baseboard and added a handle. Looking good!chain-a09

Linking Links

I’ve used quite a few links made from stiff brass wire – approx 1.5mm diameter. You can see one of them highlighted here in the Mary Chambers model. They are quick and easy to use but do have their own problems.
link-05To use the wire links I make a loop at each end with a pair of pliers  I can then thread a screw through the loop and into the model making a rotating joint.

Two problems that I’ve run up against:

First, it is very difficult to make fine changes to the length. Shortening a link can be just about done by adding some bends into the wire or by re-curling the end loop but it is not easy do do accurately.

Second, I’ve run the wire through a hole drilled in the base board, if I need to take the link out for any reason I either have to cut the wire or unfold the loop at one end. Neither of which are very satisfactory.

Here’s my attempt at a solution. I found a three amp connecting block strip in the  shed.

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Cut off one section and cut away the insulation plastic with a pair of side cutters.

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Leaving the brass block and two screws.

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Perfect! Thread the link wire in from each end and tighten the screws. Simply unscrew to make adjustments or to remove the link completely. Ta daa!

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Mary Chambers Automata

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I delivered the completed Mary Chambers model to Archives yesterday. I’ve painted the base white making the gears stand out nicely. The mechanism is working well so far – we’ll be testing it out over the next few days to see how it stands up to rigorous use. Fingers crossed. Check out the YouTube video here:

The various gears fit rather neatly into this single arch. From left to right the various gears drive first the oars, next the bobbing motion of the boat and finally the swishing back and forth of the waves.

 

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The 12v electric motor has a built in gear box reducing the speed to 145rpm – a reasonable starting point to drive the wooden gears.mary-a05

 

The fastest output speed is used to drive the rocking motion of the waves, The waves are linked to the drive shaft by a brass wire. The thickness of the wire gives a nice balance between stiffness and flexibility.mary-a03

 

Looking good I think you’ll agree!mary-a04