Progress Page 7

Rear Derailleur
A complicated part like the rear derailleur starts by thinking about how to break down into simple pieces.
7-1a

7-1b

 

 I transferred the drawings to small pieces of plastic and cut them out, using a sharp hobby knife.  It's better drilling holes as shown, and cut the inner openings first, because it's easy to hold the plastic sheet.  Once all openings are cut out, I carefully cut the outline, and slowly removed the excess plastic by using a new blade.

The teeth and curves were filed and cleaned with a very small needle file of 0.7 mm diameter.

Finished the tensioner sprockets and their frames are shown.
7-3a
 I used 0.5 mm brass rod to fix the sprockets to the frame.  I installed the chain for testing, and it looked good.  The sprockets rotated as they should.

7-3b

I cut the brass rod short, and filed the end to fix it to the frame of the derailleur.
7-2a
 7-2b

7-4

 The derailleur has two arms, which allow the tensioner frame to shift sideways, and they were made from plastic sheet.

A small piece, shown in this picture, was made from a laminated plastic.  When making a complicated shape like this, find a side, which can be easily cut, and leave that side attached to a big piece as shown, so that you can hold it easily, while carving the other sides.
7-5a

The last piece was the base of the derailleur, and it was made with a combination of 2.0 mm plastic rod and two 1.0 mm plastic sheet.

I applied super glue as putty, and after basic shape was made, I used a needle file to form the final shape.

The arm was glued to the mount, but I installed two short brass rods to the mount and the tensioner, so that it could move freely.  (Compare 5a and 5c)

7-5b

7-5c
7-6a

7-6b

 I peeled off a part of vinyl from a small cord, which I usually use for car modeling, and I twisted the metal wire to simulate the braded look.  Then, I glued it to the derailleur and fabricated the rest of the detail with plastic sheet.

 

Photo 7-6b shows the completed rear derailleur.

 

 

Another assembly was finished, but there were many more to go.  Next is the front derailleur, which is another complicated part.

 

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