day 3

has been a long one. it's been about as hot as it gets here in Tempe, high of about 115° F today.
so i did a little more TIG until it got really hot, then took a break inside for the hot afternoon. around 7 Chris came out to the shop and we worked until midnight. still working on putting couplers on that Ti Merlin. problem is the ID of Ti tubing apparently isn't controlled very tightly, so the couplers don't slide in the way they should. so i'm spending a lot of time grinding various parts' IDs and ODs to make them fit. Ti is tough shit; i'm using a serious double-cut carbide burr and a lot of elbow grease and it's slow going.

he also assigned me to work on a frame that's in for repair. excessively thin steel was used either for the DT or the HT because there was some kind of failure at that joint. he had previously used a cutting wheel to chop off the whole front end, leaving the rear triangle, ST, BB shell, and some leftover weld bead. my job was to grind off the excess steel, using an air-powered die grinder with abrasive discs and Scotchbrite, leaving the tubes almost like the front end had never been there. the steel was True Temper S3, so it was again slow going. Chris says the stuff i was grinding was harder than Ti.

we did a some tube mitering on the mill for a 29er made of high-end steel (OX Plat ST and a NOVA-branded, Columbus-made 29er DT so far). Chris uses special cutters he had made at a local tool grinder especially for cutting Ti, but they also work well on steel. he showed me how to set the cutter exactly in the middle of the tube to be mitered using a Digital Read-Out (DRO): move the cutter to the far edge of the tube (just so there's no daylight showing between), zero the readout, move the cutter to the close side in the same way, pres the "1/2" button then the "Y" button, and move the cutter to zero the Y readout. sounds more complicated than it is: basically you tell the thing where the front and back are, and it tells you where the middle is.

he demoed fillet brazing at the very end, after a few beers. i assumed he'd use the GasFlux rod Henry James sells, but he explained that type of brass (nickel bronze?) work hardens as you try to grind it, so he uses regular low fuming bronze (LFB). he demoed what he called the Zanotti-Sadoff method: after tacking, flow a tiny fillet all the way around the mitered tube. then, with a cooler flame, focus heat not at the intersection of the tubes but a little away from it on both sides, and proceed to build a big fillet. this came out looking pretty nice; it needed a little filing to be really smooth but i would have been fine painting it.