Precision engineering

There’s something very sexy about lasers. Besides being commonly attached to sharks they’re also very sexy in that they can cut through 6mm stainless steel like it’s butter. That’s right folks – the drop-outs I designed have been laser cut by the good folk at New Touch Laser and delivered to my door. I’ve got 10 sets cut, which means there’s a run of 10 bamboo bikes being built in the very near future!

Here’s some pics of the drop-outs, me tapping the thread for the derailleur screw in and how they’ll integrate into the bamboo chain-stays:

Getting a jiggle on

I decided to splurge out on a better jig, as the home-made setup I was previously using was a bastard to adjust and get everything level and straight. So I ordered some Maytec aluminium extrusion and components and now have something that’s a lot easier to work with!  Here’s some pics of the new setup:

Something to ponder

“We bear in mind that the object being worked on is going to be ridden in, sat upon, looked at, talked into, activated, operated, or in some other way used by people.
When the point of contact between the product and the people becomes a point of friction, then the industrial designer has failed.
On the other hand, if people are made safe, more efficient, more comfortable—or just plain happier—by contact with the product, then the designer has succeeded.”
– Henry Dreyfuss

Bamboo Bike Frame Strength Test

Above is a video of my homemade frame testing apparatus. It’s far from scientific, but good enough to satisfy my curiosity as to whether or not the frame passes the AS/NZS 1927:1998 Frame & Fork Assembly test. The method described for the test is as follows:

Method

(a) Anchor the rear wheel axle attachment points.
(b) Apply a force of 890 N to the front axle attachment point towards and in line with the rear wheel axle and from the deflection reading compute the energy absorbed in joules.
(c) Should the energy absorption reading at 890N be less than 40 J increase the force until this figure is attained.
(d) Release the loading.
(e) Examine the test specimen for any signs of fracture or permanent deformation. The examination shall include the fork steering tube. The examination for fractures shall be done at ×5 magnification.
NOTE: This test applies equally to rigid and suspended frames. When testing a suspended frame the energy absorbed in reaching an applied force of 890 N can be expected to be substantially more than 40 J.

Theory

Based on my understanding of physics Joules are calculated by the formula: Work(Joules) = Force(N) x Distance(m). So to get the frame to absorb 40J of energy I have to make it move 45mm (40J = 890×0.045). So I set up my rig to shift the frame 45mm up from its resting position, then applied a force to the rear axle that pushed the frame forward by 45mm. The frame was blocked by the end of the rig thou so it couldn’t move, thus the force acts through the frame, causing the front forks to bend a lot!

Result

It seems to have passed the test. There was no cracking noises or breakages. I’ll pull apart the fork tonight and make sure the carbon steerer has survived and inspect the frame for cracks or deformations.

Laser-cut drop-outs

I’m in the process of designing the second bamboo bike and have decided to go down the route of making custom drop-outs. The ones I sourced for the first bike were OK, but they needed a lot of modification in order to get the bamboo and carbon fibre to sufficiently adhere to them (I had to extend them with threaded rod). The pic of the ones I’ve designed below feature a series of holes drilled through the metal, which will provide increased surface area and grip for the epoxy resin to grab onto. A 10mm wide and 50mm long slot is cut into the end of the bamboo poles and these holey tabs will slot in and then be wrapped in carbon fibre to join them.

If anybody knows of a good laser cutting service here in Melbourne, please let me know.

Over the finish line

After some 5 long months the first bike is finished!

I’ll write more up soon, but first impressions are it’s a sturdy smooth ride. 10.2kg with the current build on it, but could easily get under 10kg with some lighter wheels.

Many thanks to Huw, Scott and Tristram at Commuter Cycles for the constant good advice and for building it up for me. Brilliant job!

Here’s some pics of the final building and finished bike:

form over function

I’m not normally one for superflous veneers, but when given the opportunity to pimp my bamboo bike even more I just couldn’t resist.  With 2 hubs in tow (one new, one old), I measured the diameters between the flanges and got to work chamfering, splitting, gluing and sanding these bamboo veneers on. I’ve coated them in beeswax to protect them from the elements. I’ll need to reapply that every so often.

High gloss

Two layers of top coat later and the frame’s all finished!  It’s not the smoothest of finishes. There’s a few carbon fibre/cat hairs stuck in there and imperfections of my sanding back are clearly visible. Still, it’s just a prototype and doesn’t look too bad from afar.

The final processes haven’t been without drama though. During the drying process a few hairline cracks appeared on various parts of the frame. To mitigate further crackage I’ve wrapped the affected areas in carbon fibre tow (which are the black bands you can see on the down tube and chainstays).  The cracks are caused by the expansion of the bamboo at high temperature during drying (ie. around 80 degrees). I don’t expect it to crack any further, unless we get a severe heatwave…

It’s now off to the shop to get parts fitted. Hooray!

Sanded back

Today I put the last 2 layers of carbon on the seat-tube and then finally got to unwrap all the tubes and sand back the joints and bamboo.

Here’s what she looks like now:

The only things left to do now are:

  1. Drill a hole in the rear bridge for caliper brakes to mount
  2. Bind a small amount of carbon around one of the rear stays, which has developed a hairline crack during the build process.
  3. Coat the entire frame in “clear coat” (an epoxy based varnish)
  4. Put on parts!

Finishing touches

Today I’ve put the first of the final touches to the frame – a carved bamboo head-tube Cognitive logo. It’s a bit simplified, but that’s ok as it will probably change down the track anyway.

The only things left to do now are two more layers of carbon on the seat tube and then to unwrap all the tape, sand it back properly, and add some final clear coat as a protective varnish layer.