How to build your very own Ti Gear Box Bike by Alan Hawkes.
O.K where to start, the big question is why? Well why not? I've made downhill frames before using t45 steel so I thought if I was going to build a gearbox DH bike then I may as well do something special. There is probably no advantage in having titanium over alloy but if you're only going to do it once then why not make it different?Racing every weekend you see some sights, Big Hits with Super Monster Tee's, zero throw stems, 85 spacers under someones stem and even Wulf Sport clothing that would make your toes curl.
Luckily for you lot I still keep my eyes peeled and my old mate Alan Hawkes wheeled this little beauty past me. A quick karate chop and he was stopped in his tracks. He promised to get her polished and some pics and words how this little beauty came about..
The following words by Alan Hawkes.
I bought a G-boxx over a year ago after enquiring via Karl Heinz at Nicolai, so that was the starting point, after I'd decided on titanium the next problem was where to get the material as it can be quite hard to get the sizes you need hence some compromises.
I work in motor sport engineering, so I was lucky enough to get a piece of 60mm dia. ti tube for the down tube, which I then ovalised. The head tube is made in three parts, two rings for the headset to sit in and the center part is made from rolling up a piece of 3mm sheet ti, this was then assembled, welded, then final machined. The mounting for the gearbox is again made from 3mm sheet, folded carefully on a fly press just using eye to fit the contour of the gearbox, not easy!!
The most time consuming part was the swing arm pivots, machined from billet titanium, probably a good days work there! No CNC machines for me unfortunately. Even the seat tube had to be machined from a solid bar, if you were to make a few you could justify getting parts machined or water jet cut but for a one off it's not really viable.
The two top tubes are 19mm dia. and I even had to make a tube bender so I could get the desired angles. The actual assembly and building was not too difficult but then is my trade. The rear dropouts are fabricated from 3mm sheet with sliding alloy parts for the axle to go through.
I drew up the suspension layout on a board and made various pieces of metal until I got the desired amount of rear wheel travel for the shock length and to get a rising rate, then once that was done I could machine these parts from alloy, these are not yet really finished but I wanted to make sure everything works OK before I spend hours machining something just to make it look prettier!
So once I had all the parts all I had to do was put it all together, simple really. I made an 'L' shape jig into which I clamped both wheels at the intended wheelbase, then fitted the forks and head tube, set these at the correct angle, fitted the gearbox onto a mounting plate on the jig, then basically measured, cut, ground and offered up the down tube until it fit perfectly! Then I did the same with the rear end, then made a separate jig so I could weld the swing arm without distortion.
Refitted the swing arm then attached all the suspension parts, then made another fixture to hold the seat in the correct place and cut and bent the tube to fit between the seat tube and head tube. Then just a case of welding it all up and off for test rides.
The first proper ride I had on the bike was at the first round of the Caersws Cup 2009 so a baptism of fire really! Only a couple of minor issues with the chain really but these were soon sorted.
So that is how you build a titanium gearbox bike, I'm never satisfied so I have already started building another bike, this one is going to be more conventional though, made from t45 again and seven inch travel with single crown forks, hoping to get a lightweight downhill/freeride bike, hopefully by July, so I have a lot to do.
Alan Hawkes
Alan, many thanks for your detailed words and inspiration to all Meccano players out there.
Stay Unclipped!
Si Paton.
Descent-Gear.com Troy Lee Sprint Shorts 59.99GBP Posted
But...those welds are contaminated, embrittled and the frame is going to break. Welded titanium should show no color at all or at most a light straw brownish color if it was kept sufficiently clean and this bike doesn't appear to have been cleaned properly nor has it been welded properly. I wonder if the frame was purged during welding? I sincerely hope that the first failure is a minor one.
FWIW - I make my living welding and fabricating titanium.
You don't have to weld ti frames in an argon chamber, but the inside of the frames must be purged with Argon and all other air must be expelled before weldling. Most people in the bike industry use purged heatsinks, baffles, dams and foil to protect the weld zone from absorbing oxygen. It's also necessary to use a much larger gas lens and nozzle that bathes the top surface with argon. You can't weld more than about 1/2" of joint with a standard cup&nozzle without getting contamination.
i have been trying to build a suspension design based around the honda unit pro link or the ktm rc8 design, but other mtb companies are doing as well so i'm just keeping a relatively simple design on my next project, after all look at the time that separate the world cup riders and they are all on various suspension designs, so whats best? all i'd say is don't believe the hype, simple is often the best, just get a good shock set up and ride hard!!
Ive never welded Ti, but id give it a go.
You live about 5min from my mum and dad. (providing that you live in Banbury, like the photo sujests).
How much did it cost to make that frame? and I cant find a G-Boxx anywhere for sale!
Ive got a good metal supplyer, but havent got any room for jigs atm (want to knock out some lightweight DH/Freeride bikes as a hobby).
How much does that bike weigh?
Dave
I seen your frame with G-Boxx. Congratulation!!
Have you build now your new frame? My dream is build a bike in titanium like you with g-boxx and this year I would like design for next year build the frame. One question more. When you buy the G-boxx? Have you a contact or email? How much? Thanks,
Best regards,
Pedro Jerónimo from Canary Islands.
See this freeride videos from Canary Islands,
RUTA VALLE SECO
www.vimeo.com/6616260
RUTA PUNTA HIDALGO
www.vimeo.com/6613901
Hmm, motor sport engineering, more "conventional" t45 (conventional in the UK) and into assembling all kind of metal tubes... Sounds like normally more into roll cages / tubular chassis.
I have done plenty Ti welding my self to know that that the welds do not look right (even through the pic)
some of the welds haven't forged enough to have the strength to hold a heavy rider and the coloration in the metal, if the weld was done correctly, there should not be any blue heat markings, when the coloring is there it means that the Ti is now contaminated and is much more at risk of cracking.
the crakes wont show up for a while but i would recommend keeping a very close eye one those welds( especially at the head tube.
I have to get startet in building my own DH bike. I have tought alot about building a ti DH bike. But the material is very expensive...
You know what it weighs?
a thing of beauty
i'm very interested in the freeride /trail bike version
(it also has no paint)
Nice indeed.
Looks like it's largely based off of an RMX? From what I've seen, it's a worthy design.
I love it!!