Meet My Great Great Uncle George.

When I told my Grandma I worked in a folding bike factory, she sent me these pictures of my Great Great Uncle George in about 1914.  I think he was in the Hertfordshire Regiment. Note the handy rifle carrier.

Great Great Uncle George

George and chum with bike folded on his back.

While on the subject of folding bicycles, I thought you might like to know that I’m progressing fairly well with my production brazing training at the Brompton factory in Brentford, having learned 5 parts out of about 15 that make up the total brazing repertoire.  The 14-mile fixed wheel commute to Brentford at 5.30am has driven me to learn to ride a motorcycle.  Don’t worry, I haven’t forsaken the True Way of pedal power, although I feel jubilant about passing my motorcycle theory test yesterday.

Today I was in the workshop making my “mixed gear” dual purpose dropouts.  The idea is that they are fitted to a single speed frame of around 73 degrees head tube, 73 degrees seat tube and shortish chainstays.  Most of the time the bike is used as an urban hack city ride with a 120mm oln rear hub except, now and then, the owner, who may not want the expense or clutter of two bikes, can fit a 130mm rear road wheel with a cassette and derailleur, some kind of shifters are added, and, as the wheel sits further back in the dropout and higher up, you get a “relaxation” of about a degree in the head tube and seat tube, and also a longer effective chainstay length, with the accompanying increased stability complimenting the provision for a rack and a mudguard.  The BB height would drop a tad too.  Now you have a light tourer to head out of the city on a few times a year; you just need a spare rear wheel, derailleur & shifters, rather than a touring bike gathering dust and clogging up the hallway in your bohemian shared house in London’s up-and-coming Hackney.

This is the idea.  Some people think the idea is crazy. Some think it’s interesting.  I hope I worked everything out properly and that the chain doesn’t get fouled on the “track face”.  Oh well, nothing ventured and all that.  It will certainly be a challenge.

All-round diamond geezer Dan Hamilton helped me get from my scribbled pictures to CAD files:

Early sketches.. will they work?

The design was simplified to be waterjet cut in the end, with 1mm faces abandoned.

Dan helped me with CAD. A nice guy.

Next I got the parts 3D printed in plastic.

It gave me a clearer picture of what I would get.

I got 10 pairs waterjet cut, with 20 accompanying track end face "extrusions". 9 pairs to ruin? and possibly 1 pair to realise I measured incorrectly? We'll find out..

I looked into getting the parts CNC milled in one piece, but had trouble getting a decent price as I was told that a special jig would be costly to make.  I thought the brazing way might be fun too.

I had the parts waterjet cut and then my engineer friend John kindly made me a little jig with drilling guides to enable me to pin the parts in place while I braze them together with brass (I originally thought I’d mill a seat for the track faces to sit in squarely, but John came up trumps with the pinning method). I chose to use brass as it’s less likely to remelt than silver if I decided to braze them into stays with brass.  Besides, I’m learning the secrets of brass at Brompton, so I have no excuses now.

Here are some pictures:

Drilling the pinholes using the drilling guide jig.

The drill press chuck wouldn't go down to 2mm so I had to add this second chuck.

John made me this neat little pin holder. 4mm lengths can be cut cleanly with a junior hacksaw, and filed if necessary.

A great way to recycle knackered old 2mm spokes. You can hold it in a vice.

A perfect little pin is made.

Jigging up a dropout plate. The hex key locks it in place.

Holes are drilled to about 2mm with the drilling guide holes in the jig. I marked the inboard sides with an X to avoid mistakes.

Then the track end "faces" are drilled to match. They will decrease the OLN by 5mm per side to accept a track hub.

In the jig.

The two parts can now be lined up for brazing.

Pins in place.

Bobs yer Muvva's Bruvva.

One pair done..

The track faces will be milled down to be exactly 5mm proud of the dropout plates:

A. Because I originally intended to seat them 1mm into a milled trench, therefore their 6mm starting thickness would be correct, and as I have now pinned them, they will be 1mm too high.

B. Because the brazing may cause them to lift and/or distort.

Next, I had to tap a 10 x 1 thread in the derailleur hanger.   I did this with some help from the drill press:

I knew those old G-clamps would come in handy one day..

I had to line up the dropout very carefully and lock the table.

I turned the chuck by hand with the key in the chuck for added leverage. I was ably assisted by my wonderful girlfriend applying steady light pressure on the drill press handle.

After backing out of the threads. I used plenty of cutting oil.

Looks like I cut these threads squarely.

I’m going to try and blog this frame build as best I can.  Bye for now.