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> Folding Bicycles V6, Folding bicycle discussion

etigge
post Yesterday, 10:57 AM

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QUOTE(KenC @ Jan 20 2018, 05:32 PM)
No need foundry to build a bike frame as per your description.If you can find chromoly steel tube, you can either weld or braze a frame up in a few hours. Minimum tools you need are a hack saw and a set of hand files. A Tig welder or a gas torch set up. A machining shop friend will definate comes handy.
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The most difficult part of frame building is getting the frame to be aligned perfectly. This has almost zero tolerance else your geometry is out. It will like those lorries we see on the road where their front tires are not aligned to their rear tires tongue.gif That's why those custom frame builders or reputable frame makers have special jigs to aligned the pieces and even with that they still need to re-adjust after the final weld.

Also important is where the welding is going to take place, ideally there should be no gap between two pieces, just a V-groove for the weld or brazing. Too big a gap, you actually will burn a hole into the steel pipes. Building a bike frame is not like welding up some 'pasar malam' tables. tongue.gif I actually have thought of scavenging old frames just to get the right diameter BB housing, headdset tubes and rear dropouts but it became too tedious. I was thinking of making a carbon fibre frame at that time. You know making a model out of wooden beads and pieces , then building the mold for it.

There use to be a custom bike builder somewhere north but he seems to fizzle out, I guess. He makes more of roadbikes and tourers. Wonder where he got his chromoly pipes? hmm.gif
KenC
post Yesterday, 03:12 PM

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Zero tolerance = no tolerance. Its only a figure of speech… In my 30+ years in engineering, there is no such thing. Everything has tolerance, for bike frame building it's +/- 1/8", or 1 Hun tolerance. That is the same tolerance I have to achieve in very coarse fabrication works… (Pasar malam table included)
Have no fear, you can always build a jig to assist your alignment. That is if you would spend time watch more YouTube lah. smile.gif
Talking about geometry… if you are serious, changing wheel size will affect the trail angle and a whole list of geometry of the bike… but does anyone care?
Welding is a very easy skill to learn, practice, practice, practice. Blazing lagi senang. Don't forget there is always Pak YouTube to consult.
Head tube and BB shell taobao got sell, cheap cheap only…
Chromoly can import la, but too tedious. I found various oversea suppliers supplying correct 4130 tube… but I have too many hobbies liao… unless I really that bored lah… tongue.gif maybe I will build a bamboo frame…

This post has been edited by KenC: Yesterday, 03:20 PM

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