The Carbon Fibre Unicycle

This failed to post itself last time so here goes again:

> Yes, after much hassle and sorting out of all the little niggly bits, my
> carbon fibre unicycle is finished and I’m rather chuffed. Originally (3 months
> ago) it was a Pashley. Talk about heavy. The biggest improvement was chucking
> the steel rim and putting on a Mavic 231 mtb rim with a skinny Specialised
> slick tyre. But it was still an excessively chunky steel frame and those
> horrid, horrid Pashley bearing mounts. So it was time to make a decent frame.
> The frame is three carbon epoxy tubes held together by a Pace mtb fork crown.
> The tubes are T300 carbon fibre wrapped 0,90 made by mandrel wrapping. They
> get a big metal rod, 25.4mm dia, soak the carbon cloth is epoxy, wrap it
> around the mandrel, cover in heatshrink tape and heat. As I only wanted a
> metre length of each of 1.6mm and 3.2mm wall thicknesses it was tricky to get
> a wrapping company to deal in such a small order but Custom Composites in
> Rochdale managed it nicely. The fork legs are
> 28.6 mm o.d., the seat tube 31.4 mm o.d. Carbon is a devil to cut cleanly - a
> hacksaw will go through it easily enough but make a mess of the tube.
> Luckily the departement I’m in had a diamond saw in the basement. Did it
> make my day to find that out? Just a tad. Anyway, perfectly clean square
> cuts to the ends of the tube and a 50 mm slit down the back of the seat
> tube to allow a bit of flex when clamping the seat post.
> The fork crown (sold by Stif in Leeds) is a beautifull piece of machined and
> polished aluminium. The tubes just slide in and clamp up. Now carbon tubes
> tend to crush if you clamp them so BERTs were needed (BERT - Bar End
> Reinforcement Thingy). These were 25.4 mm o.d. bits of aluminium that go
> inside the tubes where you are clamping them. Clamping bolt torque was
> determined by acoustic emission - I did the bolts up untill I heard the carbon
> begin to crack, then I stopped.
> The seat post is clamped by two seat collars, bought from the local bike shop.
> My Pashley saddle lasted ~2 months so I’m now running a DM. Weighs a veritable
> ton so the seat tube of the uni was extended to allow the seat post of the
> saddle to be cut down to 150 mm.
> The bearing holders were the tricky part. I replaced the Pashley bearings with
> four sealed SKF ball bearing units. Talk about a tight fit! The axle is
> slightly oversize. Consequently getting the bearings off nearly destroyed the
> bearing puller; putting the new ones on nearly bent the beefy pillar drill I
> was using as a press. The bearing holders themselves I machined down from a
> big chunk of aluminium magnesium I found lying around the lab - oh I do love
> working in materials science. Each piece started at ~600 grams, finished at
> 100 grams. Lots of machining.(I’ve a DWG if anyones desperate to see what they
> look like.) These holders just push fit onto the bearings and have 50 mm long
> cylindrical spigots that just push up into the ends of the fork legs. Epoxy
> adhesive holds them in and provides load transfer. I know this bit sounds a
> bit shaky, I mean its held together with glue! ferchrissake, but so far
> they’re solid. As for long term durability, ask me in a years time.
> Well, I haven’t weighed the whole thing but the frame and bearing holders feel
> at least half the weight of what they replace. The difference in ridability is
> immense and that’s what counts, not the polishability of it all. I came back
> after xmas and sussed idling in a couple of hours. Its so much easier to move
> it about under your self. All that’s left of the Pashley is the hub and cranks
> and, hey, I’m not sure I like the cranks either. The pedals, by the way, are
> now Odessey SharkBite BMX ones (well, I couldn’t get any DX’s in the right
> threading). Like having a pair of pitbulls grabbing at your feet. Mind you,
> get it wrong and its like having a pitbull chewing on your shins so I’m off to
> the BMX shop for some pads shortly. The first time my foot came off and the
> pedal grabbed it back I was so surprised I slammed. Oops. But i love the
> machine now. Masses of grip, seriously responsive, now all it needs is a
> decent rider.

I’ve now been riding it for 4 weeks, it’s still stupidly light and hasn’t broken
yet. I cut down some old Campy aluminium cranks, less than half the weight of
those steel ones, put them on, picked it and broke into a huge grin that lasted
most of the week. Rode Paul Makepeace’s steel 24" machine today and was like:
hey, major exercise, whats this lead weight on a wheel? Should hopefully be at
the Brussels con. in Feb so any of you europeans reading this may well see me
there falling off it.

Jez and for my next trick, a recumbent…