2011 BMC Race Machine / Colnago ct 1 / 80's Rossin / 90's Merlin/ 70's Raleigh 20/ Swift folder, etc.
extending a forks head tube
say I have a particular fork with an aluminum head tube, too short, Is it possible to extend the head tube by adding a new piece of same-size tube?
Perhaps with an inner sleeve-tube and a spot weld or adhesive?
Is it too short for the frame, or is the steerer just to short to get the bars as high as you'd like. If it is long enough to install with a headset and have a safe amount of clamping area, then you can get a bolt on steer tube extender. If is is barely long enough to install I've seen people use a 1 1/8 seat tube clamp instead of a stem and use a 1 1/8 threaded style stem. Almost like this pic from sheldon brown, http://www.sheldonbrown.com/images/iro-584-09.jpg , but with a quill stem inserted into the steer tube.
Probably not too big a deal to do. If you look at aluminum tubes in Carbon forks, that gives you an idea of the amount of overlap required for a bonded joint. The loads on a tube between the bearings will be far lower. The problem is that unless you don't need to ask this question in the first place (the likely profile of someone with a lathe, and barrels of epoxy kicking around), it will probably end up costing more than just buying a new fork. First there is the trip to the metal supplier to buy various oversized pieces of tubing that will need to be turned down to get the correct OD, ID, shoulder, and insert sizes. Then what ever may need doing if the inside of the ST is not perfect for a bonded fit-ream or bore... Then there is the epoxy to buy, etchant, etc...