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5.9 Frame Building Part 3: Finishing the fork.




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This article is from the Misc Bicycles FAQs, by various authors.

5.9 Frame Building Part 3: Finishing the fork.

Besides the cleanup of the fork, the fork needed to be aligned and the
fork crown race cut. Alignment of the fork involved four steps. First
the fork blades needed to be aligned so that the dropouts were in the
same plane. To do this we placed the crown of the fork near the end of
the alignment table and let the dropouts sit on the alignment table.
When we did this, it becomes very obvious whether the blades are
aligned. For my fork, the right blade was resting on the table and the
left was about a mm above the table (since the dropouts are on the
table, the right blade is the left blade when viewing the fork from the
front). Since the blades were not aligned properly, you can either move
the right blade backward or the left blade forward. How do you
determine which to move? One method is to fit the fork back into the
raking tools to see which blade is closer to the rake that was intended.
Another method is to hold the fork at arms length and look down the
steerer tube to the blade. Ideally the fork blade should be in line
with the steerer tube. Using the raking tool does not give an
indication of whether the fork blade is aligned with the steerer tube so
the second method is probably the better one. After some scrutiny you
should be able to determine which blade to move. We chose to move the
left blade forward. To do so we put the fork into a vice with a wooden
block holding the fork in the vice. Then they had a Park tool for
bending fork blades. It consisted of two hooks when went around the
blade and a long handle to move the blade. This again was simply brute
force to move the fork. It aligned perfectly on the first try.

The next step was to get the dropouts the correct width apart. They had
another custom tool which held the steerer tube and then a hinged metal
piece would swing down to where the dropouts were to measure the
distance between then. We needed to move each blade out just a little.
To do so just meant pulling or pushing on the dropout. It didn't take
much to move them. Thicker, stronger tubing sets take more force, such
as Tange OS mountain fork tubesets. Ron said he's hung his whole body
weight on them and only moved them a little.

Once the dropouts are the correct width apart, the next step was to make
sure the blades were centered along the axis of the steerer tube. They
had a device which consisted of a metal block with an axle end sticking
out of each end to fit in the dropouts. From this metal block a
thinner, wider metal section extended towards the steerer tube.
Calipers were used to measure the distance between this extended section
and the blades. The blades were centered so no action was necessary
here, but had there been, my guess is more brute force to and moving
both blades the same direction.

The final step was to make sure the dropouts were square to each other.
We used a nice Campy tool for this. It consisted of a pair of tools
which has arms about a foot long, then a space for the dropout and then
a larger diameter end. Since the blades had already been centered,
these larger diameter ends would meet in the middle. By looking at where
these ends meet you can determine if the dropouts need to be moved at
all by moving the handle. When finished the ends should meet as close
as possible.

Each action ultimately affects the alignment in all directions, so
ideally alignment should probably be rechecked in all directions, but
since we only moved mine small amounts, this wasn't necessary.

Two other steps were necessary to completely finish the fork, the
steerer tube needed to be reamed and the fork crown race needed to be
cut. Both of these were done with nice Campy tools. The reamer is a
solid circular blade about 6 inches long which fits inside the steerer
tube and essentially cleans it out and provides a smooth surface which a
stem can fit into. The inside of the steerer tube can get messed up
from dripping brass, hardened flux or can be bent or misformed from the
drawing of the tube, or bent or misformed from the heating caused by
brazing. The reamer is a hand tool with a long handle for twisting it
into the steerer tube, always in a clockwise motion, the way the blade
is.

The fork crown race needs to be cut so that a headset pieces will fit at
the junction between the steerer tube and the fork crown lug. The fork
crown lug is cast with a small rise above the top of the lug. Why, I
don't know, but this needs to be shaved off, down to the top of the fork
crown lug itself. Another Campy tool is used here. It is hollow to fit
around a 1" steerer tube (1 1/8"and 1 1/4" steerer tubes are finished
off on the lathe) and has blades at the bottom to cut into the steel. A
spring is put on top of the cutting tool and then a large nut is
threaded onto the steerer tube to compress the spring and apply downward
pressure to the cutting tool. Cutting oil is applied to the blades and
then the handle on top is used to turn the blade and shave off the rise
until it is down to the fork crown lug. Again, the cutting tool should
always be turned clockwise, in the direction of the blades.

The fork is essentially finished and ready to be painted. The vent
holes that were drilled for brazing will be filled in and cleaned up a
little, but otherwise it is finished.


 

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