Sunday, 4 January 2015

Making parts look right...

My Ghostbusters proton pack replica uses several pneumatic fittings that were available to the prop builders in the 80', but are no longer manufactured.
A result of limited availability and demand has led to some crazy prices for these parts.
The parts that can cause problems are: The Legris Banjo:

I've seen originals of these going for $100 each on ebay, and a resin cast replica which needs some finishing will cost over 20GBP with postage from the US.
Another part is the Legris straight fitting:

These again will cost me around 30GBP to import from the US as a pair.

So I decided to make my own.....

I asked the Iron Man of Maine to measure the ones he has, and I coincidentally had some brass hex bar of exactly the right dimentions.

I had to make two of these, so first I parted the bar:

Then I turned it down to give the pipe exit 'nipple':

I then drilled the hole to 5mm. I did this after the turning down as the nipple walls are quite thin and I didn't want to risk damaging them whilst turning down.

I then turned the part around, and reduced the bar diameter to allow me to thread it, using the oldest tap and die set in my collection. I used this as the threads of the metric dies I have seemed too coarse compared with the reference picture:

I used the end stop chuck to hold the die against the workpiece to get it started:

To create the circular depression in the top of the part, I used an old lathe tool that was made by my wife's late grandfather. This has a really small tip and is right angled to allow me to apply it to the end face of the work piece:

It came out looking really well, but too shiny. So I applied some dilute ferric chloride solution to the machined surfaces for a couple of seconds to dull them, before washing off with water:

For the Legris Banjo, I decided to try 3D printing. They came out quite well, and I smoothed them out with acetone vapour. For a brass like effect, I bought some some antique gold metallic paint. But it was too 'gold' So I added a trace of black.

It came out looking OK, but I tested it on a brass bar I had lying around:
The bottom 2cm of the bar have been painted. It looked so good I had to scratch the paint to make sure it was actually covering properly.

After painting the banjo, I think this is not too bad. I've put the parts on Thingiverse.

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