Techniques Posts

Tube Mitering on a Lathe – Updated

Tube mitering is a fundamental part of custom frame building and I am sure there is always a need to be able to produce good results by hand and eye. Paper templates are a boon for speeding up the process and increasing accuracy but I decided to see how I would get on with some form of automation for the process. A milling machine, lathe or tube notcher can all be used but as I already have a lathe this seemed the way forward. I have described elsewhere making the tube blocks to enable this. My lathe is small with 500mm between centres.
I have obtained several Coba-Tech hole saws from Stakesy’s metalwork machinery suppliers (https://www.stakesys.co.uk/hole-punches-hole-saws/hole-saws-arbors/coba-tech-10-tpi-fine-tooth-holesaws). These are fine tooth saws as opposed to the more usual coarse tooth saws I have used in the past. For cutting good mitres in fine tubes I would say these are essential and Stakesy’s were the only supplier I could find. They also sell some tube notchers which are designed to be used with a conventional drill but I have no experience of using these.

Coarse and fine tooth saws (fine on the right)

Coarse and fine tooth saws (fine on the right)

Polishing Stainless Steel – Updated

Polishing Stainless Steel – Updated

I love using stainless steel because I have always hated rust and especially when used for dropouts, fork crowns and brake bridges. It means your paintwork doesn’t get damaged. I found out how to polish it up from the instructions given by Darrell McCulloch of Llewellyn bikes fame and you can do no better than reading: http://www.framebuilderscollective.org/polishing-stainless-mcculloch/
I used to polish the parts after completing the frame but, as McCulloch, I now file and sand the parts to at least 240 grit emery paper before building the frames. It is much easier to get in all the recesses before the frame is assembled.

Oxy-Propane Brazing – UPDATE 2

Oxy-Propane Brazing – UPDATE 2

I use oxygen and propane for my brazing. I did not want the expense and extra safety concerns of storing and using acetylene, and in particular did not want to get involved in contracts given the small number of frames I am likely to build as a hobbyist. Recently small contract free acetylene cylinders have become available. Personally I see no advantage in using acetylene for building lugged frames, but it does have advantages for fillet brazing. Propane is relatively cheap and long lasting and widely available for a small cylinder deposit. I use a 11kg cylinder. Smaller ones are OK but I have found the larger cylinder more stable, especially when using a gas fluxer, I don’t know why. Storing the smallest size cylinders of practical use of any flammable gas is common sense.
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Making a template to mitre Seat Stays

Making a template to mitre Seat Stays

I wish there was a clever software program to produce mitre templates for complex seat stay mitres. However it only recently occurred to me to reduce the time it takes to shape two by transferring the mitre from the first hand carved one to the second side. I like to do my seat stays in the “fast back” style for preference instead of using top eyes. With very narrow stays it is fairly easy to shape the mitre to the back of the seat tube, but so often the seat stays are 15mm or more in diameter and require quite a lot of shaping to wrap around the back and sides of the seat tube. It never ceases to amaze me how at first it looks like the tubes will never mate, then with perseverance they all at once seem to drop into place. It does however take a lot of patience to avoid over filing the mitres whilst continually offering up the seat stay to the seat tube.

Oxy Acetylene – some observations from an amateur framebuilder

Oxy Acetylene – some observations from an amateur framebuilder

By Neill Hughes

1 – The projects:
I’ve built a couple of steel bicycle frames using fillet brazing as the tube joining method. I use standard copper based brazing rods and ‘Cycle design’ low fuming bronze flux for the main tube fillet joining and steel to steel lug brazing. All the braze-ons and dropouts were stainless steel in my projects. I used ‘tool-tip/stainless steel’ braze rod, and ‘Sifbronze tool-tip/stainless steel’ flux, for joining the dropouts. For the smaller, more delicate braze-on parts, such as bottle cage bosses and cable stops, I used a higher silver content brazing alloy, ‘Brazetec 5507’, with the ‘Brazetec D21’ flux.

Flux Removal

Flux Removal

Probably most novice framebuilders use flux and getting it off can be particularly tedious. I admit that I have only used cycle design fluxes for some time, specifically because I find them a lot easier to remove. The only effective method of removal seems to be soaking the fluxed part in water until it loosens sufficiently to be brushed off. Hardened flux that has not been soaked off seems to set like concrete and otherwise requires a lot of heavy filing to remove. The hotter the soaking water the quicker the flux comes off but I have found it takes at least half an hour of initially boiling water to get brass flux to a brush able state. Wire brushing is most effective but can scratch thin stainless steel tubes unacceptably.

Internal Top Tube Cable Routing

Internal Top Tube Cable Routing

I have done this procedure several times on completed frames, but it is sensible to do it before the tube is brazed. Partly because it reduces the chances of frame distortion when you are brazing into tubes after assembly and partly because if it goes wrong it will be easy to re-do! I have only used brass tubes for this procedure, though it would be possible to use stainless tubes if you can obtain malleable enough ones of the correct diameter. Ceeway and various model making suppliers supply 7mm diameter brass tube with approximately 0.4mm walls. You need 500mm lengths to do the job. A 7mm tube will take a complete brake cable, holding it tightly. It would be possible to forgo the internal tube and simply run the cable in and out of the top tube but I suspect this may cause unacceptable noise from the cable being free inside the top tube, and allow water ingress.

Vents and Drain Holes

Vents and Drain Holes

There seems to be some disagreement as to when and where it is necessary to drill holes in a bicycle frame, so I decided I should at least be consistent in my own practice. My thoughts on the subject crystallised when I offered to service a ten year old steel framed (Reynolds 725) trekking bike from a well known manufacturer and discovered what can happen.

David Mercer – Mercer Bikes, Cape Town, South Africa

David Mercer – Mercer Bikes, Cape Town, South Africa

I met David Mercer at the Bespoke Bike Show in London in April 2014. I was impressed with the bicycle he had brought to the show, a touring bike he called the Monkey King. It could definitely be described as multipurpose, with a lot of hand made details including custom made stainless racks. David is a Vet by training and now splits his time between working as a Vet and building custom bikes, racks and tools. He kindly agreed to answer some questions about his workshop techniques which interested me:

Brass, Silver and Flux

Brass, Silver and Flux

Thus far I have used the following filler rods and fluxes on my projects and suspect they are the most widely used:

BRASS:

SIF 101, relatively low melting point brass rods in variety of diameters, 1.5, 2, 2.5 and 3mm. For lugs and braze-ons (1.5mm) and Fillet brazing (larger diameters). SIF do their own fluxes but I favour the Cycle Design Low Fuming Bronze which I find much easier to clean off and generally better in use.
See Cycle Design Products at: http://cycledesignusa.com/wp/

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SIF No 2, slightly higher melting point and harder result. I have used this for small fillets but its main benefit is it can be used to braze stainless steel. Unfortunately in this case it needs to be used with the specific flux viz. Tool Tip/Braze Stainless flux which does not seem to melt as well as other fluxes. That said I have used it to braze a lugged stainless fork crown with no problems. Mine has come as a crystalline substance like sugar and I find grinding it to a powder with a pestle and mortar or hitting it with a hammer in a plastic bag enables mixing a much smoother paste more quickly as otherwise it takes an age to mix. It takes up water only gradually and therefore if used too quickly will harden so I even found leaving it overnight to ensure full water take up was useful. Equally when heated it dries rapidly and has a habit of dropping off the work. I spoke to someone who had used it extensively and he found it was effective used dry by warming the tubes and covering them in dry flux and also warming the rods and constantly dipping them, the heat enabling the flux to adhere.

SILVER:

SIF No 43, 55% silver solder in 1.5mm rods, 0.5 metre lengths, for lugs and braze-ons.

CYCLE DESIGN FILLET PRO, Silver solder for fillet “brazing”, also useful for filling gaps such as slotted dropouts. 2.35mm diameter sold in coils by the troy ounce. 1 troy ounce = 31.1grams, which equates to about 0.78 metres of fillet pro 2.35mm and a little over 1.8 metres of the 1.6mm diameter.
I use both the above solders with the Cycle Design Stainless Light flux which is very smooth to apply and washes off very easily compared to other fluxes I have used. Like all fluxes it come with health warnings about toxicity and it is the one flux I have used that I would wear an appropriate mask for when fillet brazing because in this situation you use quite a lot of flux and hence a lot of fumes are generated which are pretty acrid. Using it with lugs does not generate as much fume.

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