Rear Triangle

With one evening to go the final frame parts arrived for the frame, the replacement track dropouts and the top eyes for the seat stays. So with the remenance of flu still leaving me a little shakey I layered up and headed out across the garden to my workshop in sub zero temperatures. To get myself in the mood i decided to get the easiest task outo of the way, silver brazing the top eyes onto the seat stays, the picture below is before clean up:
After this is set to work on the track dropouts. The first task was to cut the chain stays to length, after this was done slots had to be cut at the correct angle into the chainstays before clamping the dropouts into the jig and butting the chainstays against them.Now the dropouts were bronze brazed onto the chainstays and the gap between the drop out and the tube filled in with more bronze, picture again before clean up: A quick cleanup of the evenings works was performed before calling it a night. Despite looking like very little work the above tasks took over 4 hours after which the flu tablets had worn off along with my motivation. Brazing produces some fairly harmful fumes so the task has to be done where there is good ventilation, in my case with the workshop doors wide open, not idea when it is minus 2 and you are not well.

At this point the frame is in the following stage of the build:
This picture is a little missleading, the chainstays have not yet been brazed into the bottom bracket, i have just inserted them for effect! The task of brazing them in is actually the simplest task left to perform on the bike but it does require very accuratly setting up the jig to make sure that the bottom bracket has the correct drop, the OLD is between 120 & 123mm and that whilst this is being done the top tube is parallel to the table top. Soemthing that i was not in the right frame of mind to do properly.

I estimate that there is around another 12 hours work left on the frame and this will have to wait until after a hiatus of several weeks.

The Forks

After ordering the replacement rear dropouts on a guaranteed next day service i was slightly annoyed when they had not been delivered yesterday so today i set about the only task left that can be completed without them, the forks.

Feeling slightly better after 2 nights of savage flu sweating, shivering and aching this morning and despite the disappointment of the parts not arriving i felt inspired to achieve something tangible on this day of rest. The first task, as always, was to construct another jig very similar to the one that i have built for the rear triangle. After this was done i measured the drop from the break boss to the top of the axle on an existing bike and used this dimension to work out the length and then to cut the two fork blades to this value, there is very little margin for error when cutting to length so it is always a slightly nerve racking experience, especially when two tubes are having to be cut to exactly the same! If i were to build frames frequently a band saw would be an excellent investment but for a one off it would have been an extravagance so i have had to cut all tubes by hand with a rotary tool. After the tubes were cut to length everything was cleaned and fluxed before slotting everything together and placing it in the jig. Once in the jig adjustments were made to give the forks a rake of 61mm (the distance the axle is in front of a virtual line drawn from the centre of the headtube) and an OLD (Over Locknut Dimension, i.e. the hub width) of 123mm, the OLD of the hub will be 120mm but a few extra mm are added for ease of insertion.The next task was the brazing, you may notice the different colour of the fluxs used on the crown and the dropouts. As i have mentioned in previous posts bronze is more suited to filling larger gaps than silver and as there was a fair bit of play in the crown i decided to use bronze for this component and go back to silver for the dropouts, the flux used for bronze brazing is pink, that which is used for silver is white.

Brazing done and after a bit of a clean up the forks are almost completed.
A close up of the dropouts:
A close up of the crown:
A fair bit of grinding down of the excess bronze will be required here as i used my standard approach for the forks of masses of excess guarantees a strong joint!

There is still quite a bit of work left to do before they are completed, firstly as you can see i left the steer tube slightly long when brazing it into the crown, i did this because it makes it easier to see when the brazing alloy has flowed all the way through the joint, this needs to be ground down level with the crown. Then a hole needs to be drilled through the crown and tapped (threaded) so that a break can be bolted on to it. Finally it will need to be polished up with the brass wire wheel along with all of the other joints when it arrives...

The frame as it currently stands:


P.S. I have noticed what i am sure will become an annoying rattle in one of the fork blades, some of the excess broze must have formed a bead and dropped into the blade whilst brazing, oh well!

New Solution

After an evening of contemplating my track dropout issue i believe that i have come up with a better solution. I have found that dropout can be purchesed without plugs, instead they come simply stamped out of a plate of steel, before hardening, which means that instead of plugging them into the chainstay where the angle of the plug dictates the angle of the dropout a slot can be cut into the chainstay and then fillet brazed into place.

The original dropouts with plugs:

The dropouts that I am now going to use:

I think all will agree that these dropouts are far less elegant but it is my only option without massively compromising on frame design.

In order to use these dropouts i will have to cut a slot into the chainstay as previously described but also to then fillet braze them into place before filling in the gap that will be created between the drop out and the tube. Silver is too fluid a brazing material to be able to do this so i will have to go back to using bronze for this particular part of the build, not somthing that i am keen on doing but i have had a lot of practice with Bronze fillet brazing whilst building the various jigs so fingers crossed it will go to plan.

Whilst ordering these track dropouts i also purchased the final component that i will need to complete the frame; the 'Top Eyes', i have opted for the C32 model.

Top Eyes are brazed onto the end of the seatstays and then fillet brazed onto the side of the toptube/downtube lug, this is the last brazing task to be performed.

Further Tribulations

Jig sorted tonight i set about cutting the chainstays to length in order to braze on the rear dropouts. After adjusting the jig to mark the position that the chainstay needed to be cut at i set about the task with a cutting disk on a rotary tool. After cutting i slotted one of the dropouts onto the chainstay and reinserted the chainstay into the bottom bracket. At this point it because obvious that the bottom bracket that i have been supplied is not correct for the track dropouts. Rather than the slot in the drop out being parallel to the ground it angled up by 3 degrees, the difference between a road and a track bottom bracket. When I ordered my components I was advised that they could supply track dropouts for a road bottom bracket but in fact after a bit of research i have found that this is not the case. Because the dropouts plug into the chainstays and a contact fit is required for brazing the tube cannot simply be cut at an angle to correct this so i am left with two options, braze the dropouts onto the chainstays as they are and except that they point upwards but his will simply transfer the issue to a differnt point on the frame, if i do this the seatstays will meet the seattube rather than the tp tube / seat tube lug again becasue the angle of the seat stay is determined by the dropout. The second option is to purchase some standard road dropouts. If I purchase road dropouts i can either simply build a road bike or modify the drive side drop out to remove the derailleur hanger and then fit a chain tensioning device to enable the bike to be run as a single speed. Seeing as the objective of this build was to build a fixed bike the second option seems like the only way forward. The downside of this solution is mainly aesthetic, a chain tensioning device will need to be fillet brazed onto the frame which in my opinion diminishes the elegance of a fixed bike. Parts will be ordered tomorrow but alas I am out of time to get the bike completed before my move to London where I will not have the space or equipment necessary to complete it. I will have to finish the build over a far more extended time frame during my visits back to the midlands.


Resolved to the fact that I can not complete any further work on the frame until the new parts arrive i directed my attention onto the forks and brazed the crown onto the stear tube using masses of silver to mitigate against impalement!

The next task will be to braze the front dropouts onto the forks then cut them to length before brazing them into the crown.

Prepping for the Rear Trinagle

After a few days of truancy from Chris Beard Custom Cycles a concerted effort was required this evening to get back on track. The goal this evening was to construct the jig that is required to complete the rear triangle. As with many things a lot of work, almost 4 hours, went into producing something that looks very simple. The jig for the rear triangle is a little more complicated than the one that i produced for the front triangle as it requires the facility to adjust the height and separation of the rear drop outs (known as the 'Over Lock-nut Distance' or 'OLD') and the angle of the top tube, actually the top tube just needs to be level but in order to achieve this adjustability has to be built in.

I began the process by attempting to weld some box section to my table 69mm apart so that the bottom bracket, which has a width of 68mm can be clamped between them. Unfortunately i had run out of Argon for the MIG welder so instead used some of the bronze, that i have from when i was considering using bronze as the brazing alloy, to fillet braze them onto the jig. After this was done the outsides of the box section were cut away and a slot cut into the inside using a plasma cutter so that they can close in to clamp the BB shell using a length of threaded bar.
A lovely fillet braze:
I produced the part of the jig for the rear drop outs by brazing a piece of box section standing on its end to the brazing table and, using the plasma cutter, cut a wide long slot down both sides to allow a peace of threaded bar to go straight through and have both backwards & forwards plus up and down adjustability. To make sure that the nuts do not simple go through the slot I produced large washers from an off cut of box section:
The threaded bar has nuts either side of the vertical box setion tube to set the height and horizontal position of the drop outs and two nuts on either side to set the drop out spacing along with the angle of the dropouts. The height of the drop outs is very important becasue it sets the bottom bracket drop, although i am building a 'track bike' it will only be used on the road so i am building it with a standard BB drop for a road bike of 68mm, a true track bike has a smaller BB drop so that the pedals to not catch on the banked track:
Completed jig with tront triangle #1 in place to help with component positioning:The next task will be to cut the chain stays to length and then to braze the rear dropouts onto them before proceeding to the seat stays.

A Fresh Start

Spirits not dampened by Seat tube / head tube alignmentgate the replacement parts were joyously unwrapped yesterday and the measuring, cutting, mitering & grinding started afresh. As all of the items that i had constructed to help build my first frame were ready and waiting it took a measly 5 hours and one late night to get back to the position that the frame was in before the disaster.


With an improved technique that can only be known by a veteran frame builder the front triangle has now been braised almost to perfection:


All but one of the brazes have been completed perfectly, albeit with surplus silver to make sure, all are structurally sound. The only error was on the seat tube / top tube lug which i allowed to get a little hot for silver brazing but this will not affect either the strength of the join or the tubing. The flux used when brazing not only absorbs any oxides & impurities that are on the surface of the pieces to be joined or are produced because of the high temperatures used in the process. It is also designed to help the brazer know when the correct temperature is reached to allow the brazing material being used to melt and to flow into the joint. The flux turns from white powder to a clear paste just below the optimum temperature, if the flux turns black the temperature has risen above the optimum point and the brazer needs to back off with the heat. When the flux turns black it will not go clear again and stains the materials being brazed. This black stain has to be polished off with a brass wire wheel, something that i have on order.

An example of a perfectly brazed lug joint, you can see that the silver has flown all the way through and around the join and the excess has coated the surrounding area:


This is the lug that reached too high a temperature, note the blackening at the base of the lug but also that the silver has completely penetrated the join:


After completing the bazing a toilet cleaner solution was used, recommended by my welding equip supplier, to clean off the worst of the flux left on the frame. This was done in my mothers kitchen sink! After using this highly corrosive solution the frame needed to be thoroughly rinsed with clean water, inside the tubes as well as on the outside to prevent it eating away at the steel over time, the frame was than placed on the Aga to dry out, note the incredibly naught dog kicking back in the comfy chair.


So now the front triangle has been completed:

With perfect alignment:

On a personal note i am incredibly lucky that i am staying in my mothers house whilst she is away on holiday for if she were to have witnessed some of the processes that i have performed in her kitchen i am pretty sure that i would never be welcome again!

Next to come is the rear triangle...

Hubris.

Everything seemed to be going so well...

After brazing the front triangle and allowing everything to cool down i took the frame out of the jig to take pride in my masterpiece, something did not appear to be quite right. On closer inspection the fault became apparent. At some ponit during the brazing process i have knocked my jig and twisted the head tube out of allignment with the seat tube by 3 degrees.
This is a catastrophic error. In a futile bid to correct it i hung a heavy weight from the right side of the head tube (as it sits in the photo above) and tried to reheat the lug to melt the silver. Unfortunately it is impossible to get the entire joint up to the temperature required at the same time and in attempting to do so i have heated the tube beyond the safe limit.

Disapointing indeed but i vow to persevere and begin afresh this time with many hours of bike building experience to better guide me. Frame no. 1 will hang from my wall so that in the distant future i will be reminded that even bike building greats such as Chris Beard Custom Cycles can succumb to hubris.