Building
A Custom Carbon Bike Part 3
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| September
25, 2002 |
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| It
has been some time, so it would be a good thing to re-establish my goal.
See the picture of my Baron by Optima. It is now 1 month shy of 2 years
since I have been riding it and I have some 13,000 miles on it. In the
interim, I have tried others, but have found this to be the most useful
for my kind of riding. I do, however, want a lighter bike so I am
duplicating this in carbon fiber with the hopes of getting a sub 20 lb.
bike. At this point, all things are working out and the project is a go. |
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| Starting
where we left off, the frame is built, but now the rear fork must be
fabricated. In order to guarantee a straight and true frame, a fixture was
constructed. Distances from a datum line to main points on the frame were
set and the frame locked in place. The distance between the rear dropouts
and a point on the frame was established (in this case it was the rear
seat pivot point). The space of the rear dropouts was set at 130 mm and
centered. The pieces of the rear fork were constructed independently and
connected by a thin sheet of 1/64-inch plywood, and the assembly attached
to the dropouts and frame. The middle portion between the front and rear
carbon pieces were built up with balsa wood. Note that there is some
thickness to the stays but it is largely hollow to save weight. The balsa
will act only as a form. |
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| Another
view of the frame, rear fork, and fixture. |
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| Shown
is a detail of the front part of the fork stays, the portion that is
connected to the main frame. Both sides were made with layers of carbon to
a thickness of .060. Sandwiched between is 5/16-inch aircraft plywood
bored out for lightness. The rear part of the fork stays (on the dropouts)
were done in a similar fashion but the picture did not come out. Some good
views, however, can be seen on the built up assembly shown later. |
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| This
is a good view of the rear fork assembled with the carbon front and rear
pieces, and the sanded balsa middle, ready for the application of carbon
layers around the balsa wood. |
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| This
is a good view of the front part of the stays, which will be attached to
the frame. Note that the right and left pieces were shown in detail in a
previous view. |
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| A
detailed view of the rear portion (dropouts). |
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| Another
view of the dropouts. Each side was made of .100 carbon plate on the
outside with a 3/16-inch hardwood center, and finished with a .060 carbon
inner. Each half bored and drilled for lightness. |
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| The
stays are now covered with carbon, joining the front and rear pieces. The
rear holes are for lightness. The front hole will receive a carbon tube,
which will be the support for the rear brake. This will be shown later.
The construction method was some 6 layers of longitudinal, cross, and
90-degree fabric, vacuum bagged and baked. |
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| A
detailed view of the rear dropouts. |
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| A
quarter view of the fork. Also shown is the tube that will join the right
and left stay, and will support the rear brake (black tube 90 degrees to
stays). |
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| Shown
are the stock parts from Optima. There is the handlebar, the tiller and
the brackets, which attach the seat to the frame. I decided that the
handlebar at 265 grams was over my weight limit and the tiller at 180
grams could also use some paring down. The seat fillings are now made out
of aluminum (rather than stainless steel) and are very light (half of the
stainless) so I will not do any modifications. |
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| The
handlebar was cut at all 3 intersections, leaving essentially only the
center portion. The right and left, as well as the middle tubes were then
machined down so that only .020 metal remained. Thee tubes were reattached
to the center portion. Then carbon sleeves were put on the bare metal (the
center portion got 2 levers). The entire assembly was saturated with
epoxy, the vacuum bagged and put in an oven. The weight was reduced by 90
grams. |
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| Shown
is the finished handlebar assembly. The weight went from 265 grams to 175
grams and I think I could have made it lighter. I will purchase various
sizes of tubes and will use them instead of creating my own by the method
of putting sleeves (carbon) over a mandrel. |
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| A
similar process was done with the tiller. It was cut but instead of paring
down the metal and reducing it with carbon, a carbon tube was connected to
it. The same carbon tube being used to tie the rear fork stays together
and brake support. Also note the collar which was milled out for
lightness. The weight was reduced from 180 grams to 145. Also note the
bottom bracket. Again, metal was removed and 3 layers of carbon sleeve
were put on. The weight went from 80 to 50 grams. See the standard thin
wall 68-mm bottom bracket next to the modified one. |
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| A
view of the handlebar/tiller assembly with the modified bottom bracket.
The next task will be to join the rear fork to the main frame and install
the bottom bracket and tube for the headset. |
