Friday, February 01, 2008
matt's bike winding down, john's bike out the door.
got john's bike all prepped and ready to go out the door. when a frame comes back from paint, you still have some work to do. you have use taps to chase the bottom bracket threads and a facing tool to make the outer edges of the bottombracket shell, the "faces" flat and parellel to each other for proper bottombracket installation and to insure longevity of the bearings - if the bearings are not held flush to each other, binding will occur and wear out the bearing races prematurely. bad! ditto with the headtube. the cups must press in equal to each other, so you chase'n'face it too. also, the seat tube gets reamed and polished to a smooth 27.2mm seatpost slip fit, and a seatpost collar made in the usa by DKG is installed to compliment each frame. then, the holes for the headbadge are drilled and tapped. it's a delicate operation - the headbadge is held on by two stainless steel bolts that take a .5mm allen wrench. when you are hand-tapping these babies you can't twitch or you will bust the tap. scary & sucky! next the threads for the derailleur are chased, as are the waterbottle holes and any other braze-ons like rack mounts, and a stainless bolt and washer are screwed into every hole. lastly, the frame is cleaned and stickers are applied. whew! off to the shipper and then to it's happy new owner. matt's bike: first picture, fresh out of the jig. the little brass globs are tacks. you only use the jig to hold the tubes in the desired geometry while you tack the frame together. the jig does not rotate on enough axis to allow you to fillet braze in the jig - gravity will pull the molten brass where gravity wants it to go, and not where you want it go. you braze in a park bicycle repair stand, constantly moving the frame as you braze so that you always have as level a joint surface as possible to lay your molten puddle. clean brazing is hard! then, a fully brazed picture. you can see the finished brazes, and the molten and unmolten flux. notice that the fillets are even width throughout, as is the molten flux denoting the heat affected zone, or "HAZ". the smaller the haz, the better. it shows that the brazier didn't overheat the metal, decreasing the lifespan of the structure. even heating also equals a straight frame. the flux cleans the metal and facilitates smooth flowing of the metal and encourages the filler metal to use capillary action to infiltrate the tight miters and develop an internal micro-fillet. flux is your friend! lastly, the frame is soaked in water overnight to remove the flux, and is given a final alignment check, and on to filing and polishing! later, steve.