Progress Page 6

Crank and Sprocket
Next parts were the crank assembly and sprocket.  Ideally, sprockets should be photo etched for a sharper edge and ease of work.  I know how to make custom photo etch parts, but I didn't have photo resistance film at the moment, so I employed more orthodox method instead.
6-1
First, I drew the sprockets on CAD.  It's so easy to draw the teeth, because I only have to draw one, and make a radial copy of it.

I use Rhino 3D for drawing.  Rhino 3D is more suitable for surface modeling for CG, but it's my favorite CAD, because it's easy to use, and it's a powerful enough for hobby use.
6-2
I directly print the image on 0.3 mm plastic sheet, using Alps MD5000.  This isn't quite recommended, because you might brake the printer.
6-3a/b
 I used various sizes of bit to drill holes around the teeth and round corners.

Then, I used OLFA's hobby knife to cut out the openings, and cleaned the edge with a 0.7 mm diameter needle file.
6-4

0.3 mm was not thick enough, so I glued the part to another sheet of plastic, and cut out the unnecessary areas.

Finished sprockets are shown, one is outer and the other is inner.
6-5
 When two pieces are putt together, it looked like this photo.

Again, I used 0.7 mm diameter needle file to trim and clean the teeth and corners.
6-6a

6-6b

 The crank was made from a laminated plastic sheet, using the template, which was printed on a sheet of plastic.

I used files and sand papers to round the edges to the proper shape, while trying to represent the proper section cut.
6-7a

6-7b

 The spider arms is made from a laminated  plastic sheet, as well.

It was glued to the right side crank, and I filled the gap with superglue.  Then, I filed and sanded to blend two pieces together.
6-8
All three components were finished, and it was time to put them together.
6-9a
 The finished crank assembly is as shown in these three photos.
6-9b
 6-9c
6-10
 I needed to make the tabs, where front and rear frame are connected together.  I cut out a piece of metal sheet and bent it, then I glued a piece of plastic shown in the picture to add thickness.

6-11a

6-11b

 The cassette sprocket should be made by photo etching for better detail, but I had to compromise with a conventional approach.

I used a part in the Audi bicycle model, and I added two sprockets at the top and bottom.

6-11c
6-12
I wrapped the sprockets with the chain, and it started looking more like a bicycle.
6-13
 The pedal was also a laminated plastic sheet.  The center piece was made with two 1.0 mm plastic sheet, and it was filed and sanded to the desired shape.

The two plates were also made from plastic sheet.  I drilled 0.3 mm holes at the top and bottom of the slits, and the slit was cut open with a sharp knife.

I attached 2.0 mm plastic rod on the DREMEL, and lathed the part, which connects the pedal and crank.

Again, small parts were made with laminated plastic sheet.  Some parts can be made with polyester or epoxy putty, and the choice of material is up to individual modelers.

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