aProgress Page 9

Seat
The shape of the seat is a little complicated because of its 3 dimensional shape.  It's also thin, so carving from a chunk of block doesn't work.  For a piece like this, vacuum form is the ideal solution, but it's too much of a work, so more simple method like heat-and-press works best.
9-1
I used tracing paper to transfer the drawing to a balsa wood, and I cut and curved the outline as shown.
9-2a

9-2b

 After finished the cross section, I sanded the top surface to match the top curve on the side profile.  

 

Then, I carefully sanded the rest to match the shape of the seat.  The piece is symmetrical, so draw grid lines, and look at the piece from various angles to help determine how much to sand.

Finished master is shown in the picture 9-2b.
9-3
 Heat-and-press method is very easy.

Fix the master with a vice.  Clamp a sheet of plastic, and heat it slowly with a candle flame.  Once plastic is soft enough, press it onto the master part as shown.  Wait for 10 seconds or so, and remove the plastic from the master.

Try making several, and pick the best shape.  I tried five times, until I was comfortable.
9-4
 		 It was a little too hard to engrave the AM (Alex Moulton) logo on the seat directly, so I engraved it on a plastic paper, and I glued it on the top surface of the seat.  Then, I sanded the surrounding area to bland it with the seat.
9-5a

9-5b

Trimming a vacuum formed or heat formed part needs a little care.  Instead of trying to cut to the final shape at a time, always leave some margins, and cut small piece each time.  

Then, file and sand to the desired shape.
9-5

 Because the seat has a texture, I used thinned putty to represent it.  I mixed Tamiya putty and GSI Creos (Gunze) Mr. thinner, and hand brushed it on the surface of the seat.  The roughness of the texture can be controlled by changing the mixing ratio of the putty and thinner, and this is very useful for other applications, such as model car interior or engine block.
9-7
 The seat frame was made with brass rod and plastic sheet as shown.
9-8
 The finished seat is shown.

I used TriMaster photo etched template to carve circles to represent the rivets.
9-9
 The side of the seat is shown.

The tensioning bolt at the front of the frame was made from a brass rod.
9-10
 Finished seat assembly is shown.  Notice the brand plate at the back, as well as the rivets.

The seat is Brooks Swift, and initially, I didn't have enough reference for it.  However, thanks to google image search, I was able to find many photos of each parts.  I recommend making use of it, when you have a trouble finding good reference photos.

Now that all parts were made, it's time to resin cast the symmetrical parts. 

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