You are reading a single comment by @hms and its replies.
Click here to read the full conversation.
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
@hms
Frame Build
Day 2 Afternoon
It's Tacking Time - joining one tube to another of the first time.. The seat collar was double tubed and robust - and so able to take a lot of heat. The main tubes are REALLY thin so go easy, says Mark.. It's possible to think you've moved the torch right off the metal but be concentrating so much on the braze rod that you waver back on and burn through a tube in just a few seconds..
Before the braze comes the flux though. It's wonderful stuff; lurking at the bottom of cut-off plastic pot with a venerable old brush in it. The brush makes you slap it on, more-the-merrier style. There is no delicacy about applying flux.. After the braze, it crystallises and seems impossible to get off, but a dousing with boiling water in the yard outside cleans them off. I had thought the kettle was constantly on for cups of tea but there is actually a work purpose as well.
We tack the top and bottom of each tube with it locked in the jig. John does one side to show me how and I do the other one. All goes well. Taking the assembly out the jig at this point is a wonderful moment. Even though its just tacked it's suddenly a self-supporting frame rather than a collection of tubes.
Mick and I compose ourselves with a quick cup of tea and then we braze for real; turning the tack into a smooth fillet. Slap on more flux, mixed into a loose paste from boric acid powder, watch Mark do a half and then go for it. Heat. Rod. Draw. Build up the fillet at the top like a bridge and then puddle to one side and around, returning to even out with the flame. A cooling ridge can be evened out by re heating and coaxing (with heat alone) into the next puddle. One side, then the other, keeping the braze width, height and smoothness as constant as possible. We've moved the frames onto mid-floor bike stands so that we can turn, turn and turn for the best angle. Holding the torch, the rod and moving the frame constantly; you always need a third hand and a fourth would generally help too.
Once the head tubes are brazed we turn up the torch heat and do the bottom bracket shell. The shell is really solid so needs a ton of heat but the tubes coming in are the same wafer-thinness as before so you need to be extra careful not to stray with the flame. Having mastered the basics now aesthetics come into play and I'm urged to keep the brass off the BB so we don't have to file it off later. It's like being told to draw in the lines at school. Pool the rod on the tube and draw it through with heat. Then go back and fill the shoulders. Oops, a spill or two. Bugger. Still good I'm told.
So I have a the front triangle of a frame but is it any good? Time to check everything on the flat surface. Lock the frame in at 90 degrees to vertical and check everything is where it should be along the length of the frame.. A tiny bend here, a micro twist there until Mark is happy.
Ream and face the headtube with tool and cutting oil.
Re cut the BB shell threads.
It's been a long, intense afternoon but the progress is obvious and I feel I'm getting into the lingo of the workshop. I know the how much to move things a "fracko" as opposed to a "dollop", and feel confident with either applying a "swiff" or a "tickle" more heat at the critical moment..
1 Attachment