Thursday, April 9, 2009

Bunn's Feed & Seed, Part 5: Silo

Building the silo was one of the most enjoyable parts of this project, and I really looked forward to working on this piece while I was nearing the end of making and installing all those finicky windows!

The basic structure is rather simple to build: cut a cardboard tube from an empty roll of paper toweling or toilet paper to the proper length, and then wrap it with 1/32 inch balsa.

Before wrapping, lightly score the balsa with vertical lines spaced a scale 6 inches apart. I used an ‘almost’ sharp HB pencil for this task. Make sure the grain of the balsa and the scoring are both vertical. The pencil will leave dark gray coloured lines along with the grooves, but once the wood is stained, they improve the overall look of the silo by enhancing the definition of the boards. Also, lightly draw on horizontal lines to use as guides for the bands, but don’t score the balsa with these lines.

I used super-glue to bond the balsa to the tube – I have no idea what Mr. Moore used. Gluing the balsa to the tube is a little tricky. Attach a 1 or 2 cm length at a time by applying a few dabs of glue to the tube in a vertical line, press the balsa and tube together, hold for a few seconds until the glue sets up, and the repeat until the balsa is completely rolled onto the tube. Sometimes, where the vertical scoring was a little too deep, the wood would split along a score during bonding. No problem. Just poke a dab of super-glue under the split and rebond it to the tube.

The horizontal bands are thin strips of thin paper. To attach them to the balsa, spread a thin layer of white glue on one side and press the band out along one of the guide lines drawn on the balsa. I made sure that the beginning and end joint of each band came together at the back of the silo in order to hide it.

Once the glue is dry, the silo was stained with a thin mixture of Model Master Acryl Armor Sand, Polyscale Mud, Model Master Acryl Flat Black and Model Master Acryl Thinner loosely mixed on an old CD – I find that old CDs make good paint mixing palettes.

[24 degree cone on left; 14 degree cone on right]
I deviated from the article a bit on the construction of the roof. Mr. Moore specifies just taking a piece of construction paper, cutting out a 14 degree wedge, and wrapping it into the conical shape shown in his construction drawing. This was a little too simplistic for me. First, I drew the circular roof plan on a piece of 0.012 inch styrene. Please note that I think there is an error in the article’s instructions for the roof: I think the wedge to be removed from the circle should be 24 degrees instead of the 14 degrees as written. The 14 degree cone seems a little too flat when compared to the pictures on the article. The styrene circle – with the cut-out 24 degree wedge – is then formed into the conical roof shape. Super-glue along the cut-out wedge edges to hold it together.
A circle, the same diameter as the silo, is cut from 0.020 inch styrene and glued inside the roof to form a base for it to sit on. Wood strips are then glued to the inside surface of the roof that overhangs the base to simulate rafters.
The roof is surfaced with wedges of fine grit sandpaper. The sandpaper is not meant to replicate any particular roofing material, it’s merely to provide some texture to an otherwise flat, smooth surface. As far as I can tell from the photos in the article, Mr. Moore left his roof as raw construction paper. Super-glue was used to bond the sandpaper wedges to the styrene.
[Silo base]
The silo base is built as per the article and then stained with a mixture similar to that used on the silo, but with less of the Armor Sand colour in the mix.
[Testing the placement of the silo]
The delivery pipe is built up from styrene tubing and painted with Tamyia flat aluminum. Prior to installation it was painted with a very thin wash of flat black to tone down the shine. The inside of the lower portion of the pipe was painted flat black.
[Delivery pipe before sanding & painting]
[Finished silo]

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