Tuesday, September 13, 2011

John's High Racer frame

Well now a spy down in Rangiora informed me last night that Mr Knight has been filing his knees, so I have had to pull m'finger out with John's high racer.

The first stage of making a High Racer is to plan everything carefully beforehand and draw it neatly and think about every bit of clearance, and then go and look on the Bike Heap for the necessary parts.

The second stage, when you come back to the drawing board, is to rip the design up and screw all the bits into a ball and hurl them across the room and start again because everything in the Bike Heap's an inch bigger than you wanted it.

The third stage is to retrieve all the bits and put them on your light box and make a sketch of the first stage, with all the alterations added.

Of course if you are a proper engineer you do not do this at all, but you and I are not proper engineers. We are rank amateurs, and leave the professional stuff to Mr Bird and Mr Burrows and Mr OtherpeoplebeginningwithB.

My Bike Heap these days dangles from hooks screwed into the rafters of the shed, a magnificent advance in amateur bicycle manufacture which I commend to anyone who possesses a shed with rafters. Unf. most of the bikes have either been sawn up already or are made of 531 tubing. The Donor Bike selected did not match my drawing, and pencils are easier than welders and paper is cheaper than steel. The next donor bike said Chromoly on the stickers but it also said Milazo and since Milazo is a cheap brand sold by the Warehouse, a New Zealand equivalent of Walmart, I knew it would be mild steel so I sawed it up cheerfully and was a bit startled to find thin-wall seamless tube all over the workshop floor so perhaps it was chromoly after all. Perhaps Milazo was a reputable company before the Warehouse buyers got to it and forced the quality down.

The rear swing-arm pivot will go through the old bottom bracket, and rather than soften and machine the cups to fit, the Dremel was applied. Only a smidgen needed removing since I wanted a 3/4 tube through it, with nylon bushes inserted and a 12mm OD tube as the actual pivot.

Preparing the hole for welding in the head tube

The mainframe is 2" OD 18g mild steel, and I used a 38mm hole cutter in the drill press to bore a hole for the 40.5mm OD head tube. This would appear to be of mildly inadequate size, but I am a Rubbish Welder as well as a rubbish everything else, so the idea is to insert a hacksaw blade through the hole and saw little radial nicks before hammering everything outwards like a mediaeval crown to enlarge the hole. It makes the welding easier, but rather more importantly allows you to delicately adjust (whack away with a hammer) the exact angle of the head tube, which needs, according to my envelope, a backward slope of one degree. This is one case where it pays to have a hacksaw cut on the pull-stroke. - I offer this gem of wisdom as my contribution to the field of engineering, and require tribute in consequence. - No autographs, sorry. This is the Internet.



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