Techniques Posts

Framebuilder Tooling – Using a Milling Machine

Framebuilder Tooling – Using a Milling Machine

A Milling Machine is usually the second major machine tool any aspiring metalworker will obtain, after a lathe. More correctly known as a vertical mill as horizontal mills do exist. Whereas a lathe mainly turns objects in a circle, the milling machine will make objects square and cut slots as well as performing tasks that can also be done on a lathe such as drilling and tapping (being more flexible for this), boring holes and sawing (using a ‘slitting saw’) and mitering tubes.
 Basically it consists of a drill mounted on a column which can be moved up and down, pretty much the same as a pillar drill. The head is wound down slowly and has an accurate depth scale on the operating handle. There is also a plunge section as you would find on a pillar drill with a large handle which can be used for rapid drilling but is locked out for more subtle milling operations. The column can often be tilted from side to side to enable cutting at an angle but in practice this is not very useful and it is usually better to mount the work at an angle. The mill can be used as a drill press. Some mills are sold as mill/drills but I am not sure of the difference. Drills can be mounted in a drill chuck but other tools are best mounted in a collet chuck system which is more accurate and secure. The drill head itself can only move up and down, so the shaping of the metal is achieved by moving the table in two axes, against the milling cutters of which there are several types. Collet chucks and the like are usually attached to the mill head using a morse taper. These have a tapped hole in the top which is to further secure them in the drilling head with a threaded bar. Unfortunately a lot of potentially interchangeable lathe tools have a tang (a projecting bit of metal) which is to facilitate their ejection from the lathe tailstock. This means they will not fit into the mill head. I am mystified as to why tooling manufacturers do not make interchangeable tools.
*(Belatedly I have discovered my mill can accept tools with a tang by fully extracting the drawbar, I do not know if all mills are capable of this. I have not seen any reference to it anywhere so it may well be worth asking if you are considering a specific purchase)
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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

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: