Sunday, 17 February 2013

A Sling Cart

Google "sling cart" and you will come up with something like this:
These were used to move large fortress guns.  Note a fairly standard artillery limber to lead (left).  The central portion is a large wheel with (at my count) 24 spokes.  Note how the wheel is "dished' to both sides, and how the spoke spacing does not seem equal.  It looks to me like the inner set of spokes is 16 evenly spaced spokes. The outer assembly, looks to be only 8, for a total of 24 spokes.  The trailing unit is a single sided 16 spoke wheel. So, if I can figure out how to cast this thing, I could cast up 4 identical wheels, and two outer bits to make the central unit. Based on drawings I have seen, the central unit appears to be some kind of 'bottle-jack' while the trailing unit is a central screw and a handle to crank up or down. There is also an etching that shows a gun sling being towed by a hundred or so men. These guns were heavy and you didn't always have horses or mules available...
This shows a plastic ring taped down onto my building jig. The central hub has a spacer, a ring to set the spokes on and an outer spacer to form the hub. The jig is marked for 8 equally spaced spokes. Individual spokes, in this case .040 by .060 Evergreen strtip, are cut and fitted. A small bit of .040 sheet raises the outer end of the spoke to center on the outer rim. The spokes angle upwards slightly as they merge at the hub.

This shows 16 spokes for the inner and standard wheel.  The spokes were glued in place at the rim and the hub with Testor's liquid solvent.  Note the drill bit used as an axle for temporary allignment. It has a couple of turns of masking tape on it. This allows a bit of downward pressure to be put onto the hub.  If the spokes are a little tight, the hub tends to lift off the building board. The tape on the drill allows you to press it back into position.

However, before I started the 16 spoke wheel, I made a "spider' of a section of the hub and only 8 spokes. The 8 spokes were glued only at the hub and carefully removed as an assembly when the glue dried.

This shows a trial assembly of the 24 spoke wheeel.  Note the outer disk on the hub. This strengthens the spokes, and a bit of green stuff will fill in the gaps at the hub around each spoke.
See how the wheel is "dished" on the inner and outer surface. I originally thought the spokes were a little thin, but I think the wheel matches the spirit of the picture if not the precise dimensions.
So here is a 'master' for the wheels with the Redoubt VMI cadet for scale. This figure is a large 28, so the wheel will look even bigger next to my 'standard' Old Glory 28s.

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