Build Up

 

Once the carbon fiber finishing work was completed, it was time to turn my strange looking plywood and carbon sculpture into a bike.

The first step was to complete the frame by installing the head tube, front derailleur tube,  bottom bracket shell and rear swingarm.  A friend who is a machinist made a head tube of 6061T6 aluminum for me based on the drawing below:

This headtube was designed for a 1" headset.  One noteable feature of the headtube design is the small step in the outside diameter one inch from the bottom (from the left side in the drawing).  The step was to rest against the underside of the frame, and prevent impact loads on the fork from pushing the headtube up into the frame. 

To install the headtube I first applied a layer of epoxy inside the hole previously drilled for the headtube, and let it cure.  The purpose was to seal the wood so that when I later epoxied the headtube in place, the epoxy would not soak into the wood, leaving the joint starved of epoxy.  I prepared the aluminum headtube by scoring the surface with the edge of  file and then etching the surface.  Etching is necessary to form a strong bond between the aluminum and the epoxy, as it removes the thin layer of aluminum oxide that forms on the surface of aluminum and interferes with bonding.  I used the West Systems etch kit that I bought from Aircraft Spruce.  With the bike frame clamped upside-down in my Workmate, I applied epoxy to the surface of the head tube and slid it into the hole in the frame.  After that cured I turned the frame over and applied epoxy around the circumference of the tube where it met the frame, making kind of a filet of epoxy at the joint.

For the bottom bracket (BB) shell I used a steel version that I purchased from Power On Cycling.  I considered using an aluminum one (for weight reduction) but chose a steel one instead because it came with an OD of exactly 1.5 inches.  The aluminum shells came with oddball diameters that would have made finding the corresponding drill bit difficult.  I epoxied the BB shell in place using virtually the same procedure as for the headtube.  Since the BB shell was steel, no etching was necessary.  Also, since the two sides of the BB shell are threaded opposite (one is left hand, the other is right), I was careful to install it in the correct orientation, although at this point I don't recall which thread goes on which side.

I used a 1.0" x .058" aluminum tube (from Aircraft Spruce again) for the front derailleur tube.  Using a 1.125" or 1.25" diameter tube may have been better, as this would allow installing the front derailleur without the need for a shim.  However, I used the 1.0" tube just in case I later decided I needed an eccentric shim to fine tune the position or orientation of the front derailleur (I didn't).  Like the head tube, I first etched it and then epoxied it in place.

This image shows the bottom bracket, front derailleur tube and head tube.  Note the shim under the front derailleur clamp.  For the front derailleur cable stop, I used a plain aluminum collar from McMaster-Carr, with a hole drilled into it to seat the end of the cable housing.  I also filed it down quite a bit to make it less crude looking.  I really like the exposed wood at the front end.

This picture shows the exposed wood at the other end of the bike.  Forty-five plies of birch, count-em!

For the two attachment points for the rear swingarm, I also epoxied aluminum sleevess into the wood frame.  These sleeves were turned on a lathe to the necessary dimensions by my machinist friend. 

This pic shows the attachement of the swingarm to the frame, as well as the TerraCycle over/under idler.  Originally, I used a Greenspeed idler for the drive side and a teflon chain tube to guide the return side over the front wheel and v-brake.  This was the setup I had used on Woodyie and is shown in the two pictures at the top of this page.  The over/under setup is much better, eliminating the need for the chain tube and the resulting noise and drag. The chainkeeper on the bottom is just a piece of aluminum that I bent in a few places and screwed to the bottom of the frame.  I thought I would need a chainkeeper on top too, but the chain hasn't popped off yet, so it looks like I don't.

At first glance the two pics above look identical, but they are not.  Note that the idler wheel floats on the axle depending on the choice of rear cog.  When I first installed it, I was very disappointed to find that the TerraCycle idler did not float as well as the Greenspeed idler did.  So I called Pat Franz at TerraCycle and he explained how I could reposition the two bearings to more "outboard" positions.  After making the change it worked great.

A critical step to making the over/under idler work was eliminate the chain interference with the front brake.  Replacing the front V-brake with a Bacchetta caliper did the trick.  It gives the bike more of a roadie look as well.  I did lose a little braking power compared to the V-brake, but got most of it back by installing Avid Speed Dial brake levers and adjusting them for maximum leverage.

This shows the brake from the opposite side. The top of the brake just barely clears the bottom of the frame.  It also shows a good view of the fork.  I got it from Bill Cook at Barcroft, it's the one he uses for the Virginia GT.  I really like it because it's light and looks sleek.  I wish I could get one without the brake bosses.

The rear brake is an Ultegra long reach caliper.  To mount it I made a brake bridge out of an aluminum plate and attached it to the top of the swingarm.  Okay, I admit it, my friend made that too.

The seatback is a sheet of aluminum, .032" thick, bent into shape and screwed to the frame.  Unbent, it felt very flimsy, but the bends really stiffen it up.  The holes are for weight reduction and ventilation, but since I never got around to putting holes in the pad, the vents don't work so well.

The attachment of the riser to the fork steerer tube is unique, at least as far as I know.  The riser and steerer are each inserted into a sleeve about three inches long, butting against each other in the middle.  At the top and bottom of the sleeve are clamps (seat post clamps, actually).  The sleeve is slit along it's full length to allow the clamps to squeeze the sleeve firmly to both steerer and riser. 

This arrangement allows preloading the headset bearings as follows:  I loosen the top and bottom clamps and remove the riser, but leave the sleeve in place.  I position a headset cap on top of the sleeve, put a bolt thought the cap into the star nut in the steerer and tighten as I would for a normal threadless headset.  I then tighten the bottom clamp, locking in the preload.  Then I remove the headset cap, insert the riser into the sleeve and tighten the top clamp.  Works great.

This image shows the "ventilation" holes in the seatback.  I put some automotive door edge molding around the edge of the seatback, which gives the seat a more finished look.  Mostly, though, this is a gratutitous image of the finish on the carbon fiber.

Above, two views of the cockpit.

For the rear wheel, I made nylon wheelcovers based on Alan Ariels' design.  The rear wheel and wheelcovers came directly from Woodie.  I rebuilt the front wheel, for no particular reason, using only 16 spokes, skipping every other pair of holes in the rim.  After several thousand miles it runs as true as the day I built it, so I guess it's okay.

Ready and waiting for the next ride....