Saturday, April 10, 2010

Bender's antenna - part 2

Before I get too far into the ball and how the antenna holds together, I found this slightly blurry photo of the washer pressed into the bottom of a deodorant lid to stop the lid collapsing in the lathe chuck. The washer was nothing special, not even properly round, just an old thrust washer from the junk box.
So, I've mentioned the three components which make up Bender's antenna.. the ball at the top, the tapered shaft in the middle, and the dome at the bottom.
The ball in this model was an old deodorant ball (Lynx if it matters, but they all seem to be the same size). I considered gluing it to the model, but didn't trust the join. I decided the best approach would be to affix the ball to a shaft which ran through the tapered shaft, and was retained in the dome, or valve. I drilled a 1/4" hole in each of the balls, and then prepared some 1/4" shaft. The shaft was threaded at the end which would be away from the ball, and the "ball end" was hacksawed for a length of around 20mm (3/4") along the middle. I then made 2 small wedges of scrap steel which had a narrow point, but then a steep taper followed by parallel sides of 1/4". The point was to allow a friction fit in the hacksawed slot, the steep taper to force a wide split in the slot once driven in, and the parallel section just for length.
The idea was to use the wedge to lock the ball onto the shaft by making it wider than the 1/4" hole. I mixed up some 30min epoxy resin, and filled the inside of the ball with a 50-50 mix (by volume) of resin, and brass swarf (from under the lathe).
I put the wedges in place (held with a single turn of sticky tape) and carefully inserted the shaft into the ball via the hole, then tapped the shaft down against the wedge so the shaft would expand inside the resin filled ball. The photo below shows the two balls with their shafts waiting for the resin to cure.

The photo above also shows the dome and shaft assembled. This was done by half filling the dome with some expanding foam, then forcing the turned valve and shaft into it and letting the expanding foam lock in under the lip I turned. Once the foam was set, a simple trim with the knife cleaned away any spillage, or leakage.
I tried using a smear of the foam to fill the small gap in the ball seam, but it didn't really take too well.

The threads cut on the end of the shaft (with a die - I'm still working on building a driven leadscrew for my Taig) were matched with a brass sleeve nut I made up on the Taig. The brass was bored, then tapped for the thread, and then finish turned for the stepped bore in the valve. Once the lengths were finalised, I bored out some of the threads for easier assembly, and cut a tool slot in the sleeve nut. A similar tool slot was cut in the underside of the valve threads to make assembly easier. With the ball on one end of the shaft, and the nut at the other, the tapered shaft, and dome were locked together on the cut down valve, and the whole assembly was then placed on a spare extinguisher top for the last photo.

This extinguisher top is how the NuSwift DCP looked before I started cutting them apart - a large bronze boss in the top for the valve assembly, a smaller boss in the middle of the curve for the pressure gauge, a carry handle on the back.
A total of five extinguisher tops are used to make bender, one for the head, two for the feet cups, and two more which are cut up for patches on the others where the gauge bosses are cut out.

Why do I seem to have so many old fire extinguishers? I grabbed them when I was building and using my furnace/foundry. I was using the bottom halves to make cheap low use crucibles for my aluminium, brass and bronze furnace. I never threw the tops away since they had those big bronze valves, and bosses - the intent was to melt them down for stock. When I got the NuSwift DCP extinguishers, there were other extinguishers in the pile I could have had, but there was considerably more NuSwifts than any other type. Once I started bender, I would regularly collect other extinguishers to cut up for the arm and leg segments, but that didn't work out as well.

I will do up a page (or several) about the furnace and it's tools (including the "robot"), but that will be after I complete the documentation of Bender.

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