Here is again the original head tube slaughtered from the Condor donor bike. Its length is about 15 cm. I started by disassembling both upper and lower head tube bearing races. They will be reused along with the complete head tube set in my new frame.
I cut to length, nearly by half. The problem is that the top and down tube are brazed to the head tube using lugs. To utilize the lower part of the original tube I will have to cut out the lug for the down tube.
Here the cut head tube can be seen mounted in the lathe. To turn it perfectly centered I had to prepare a wooden plug to fix the counterpoint.
Here it is before...
... and here it is afterwards. It took some time to center the workpiece accurately, but it was worth the effort, as I did nicely shave out the complete lug and old brazing material. Many of you could ask why did I not use the torch to melt the old brazing joint instead of taking the trouble to turn the piece into the lathe. The reason is that I am using just a propane torch and a brazing alloy with a solidus temperature of about 600 C. The brazing alloy used by the original manufacturer was probably with a much higher Copper content and a higher melting point. When I slaughtered the donor frame I tried to melt some joints with the propane torch, without success. An oxy-acetylene torch would be needed, which I do not possess.
Notice that in the right there is still the original brazed ring at the point where the bearing race is fixed. Since I did cut the original head tube, I have lost the ring in the left, ergo the upper ring. I will have to manufacture a new ring out of the remains of the head tube to braze it in place later. I was having a rather oriental mood that day, as you can see from the original japanese tea pot and tea cup that can be seen in the picture.
Once the main tube was under control, I turned my attention to the pieces I will braze in place for the fixation point of this head tube to the frame. I started from the other half that was recycled from the original head tube. I filed the lugs out to get it clean and cut the tube open longitudinally in the back. The whole idea is that I need another tube of slightly larger diameter that will be brazed as a lug on top of the head tube. As the recycled tube for the lug is of the same diameter as the head tube, I cut the tube in the back and forced it open carefully so that it perfectly fitted the head tube. After that I have to manufacture the rear part of the assembly that will provide the fixation point.
I took the trouble of carving the badge of my bicycle brand in the jacket piece that will contain the head tube. As my very special mark I selected a three-leafed shamrock. Nothing to do with Ireland, if you ask. It is a symbol that has some tradition in my family, as my grandfather used this mark long ago for livestock branding at his farm.
It took some time to carve such a design, but it was worth the effort. In the first blog I promised that this was about "rolling scupltures". Well, not yet rolling, but sculpture it is.
To manufacture the rear part of the head tube support I formed 2 plates 2 mm thick and brazed them together. I carved one finger each side with a puzzle-like shaped for a perfect fit with the front part.
Front view...
rear view...
Perfect fitting. Notice the upper ring still missing.
Machining the upper ring.
Assembled and fluxed. This is going to be the most complicated brazing joint so far. It is very bulky and therefore, it is difficult to apply heat evenly. It consists of many pieces and with large contacting surfaces that require very accurate heat application so that the filler alloy will flow properly.
It went well after all. I would not describe it as a surgical procedure, but solid it is, without a shade of doubt. This is how it looked immediately after brazing and without any cleaning yet.
After cleaning... Note the upper ring, nicely brazed back in place again. Note the jig-saw puzzle shapes nicely fitting.
I drilled the hole for the shackle, as I was impacient to see the whole assembly. This is how it looked. I tried and filled the shamrock with brazing alloy, but the result did not impress me. The contrast between steel and Cu-Ag-Zn filler material was not very sharp. I will better cut the shamrock again out of copper sheet and braze it in place in the carved recess.
