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Building frame


Kenny--Trials

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Right so, i haven had a trials bike in a while now (about 2 years) and since i have started a job doing aluminum/steel fabrication so naturally i want to build my own frame :)

Im currently trying to draw up the frame design on solidworks 3d cad so i can make a jig from that and then get to putting it all together but just the cad drawings are proving impossible because i dont have anything to measure off. The tartybikes videos do help explain where the dimensions are from/to but im having trouble with things like:

- the internal size of the head tube

- bottom bracket cup length, thread size and internal diameter (without thread depth)

- typical tube diameters for top tube, bottom tube, chainstays, ect

everything else i could probably do, any help/advise would be greatly appreceated

thanks

edit: if anyone knows how the offset on forks work that would be handy too

Edited by Kenny--Trials
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It's kind of neither, but I think you probably just used the "wrong" words for what you intended to mean with the first one.

If you ran a line down the centre of the steerer tube and extended it all the way down past the dropouts, the offset is measured perpendicularly to that.

The axle-crown length line would be the line that a straight-bladed fork leg very nearly follows.

Standard headtube ID is 34mm, I think, and Euro BB ID is 33.5, again, I think.

Tube diameter varies wildly from frame to frame, though for a rough guide: ~45mm downtube for a "regular"ish look, or ~50mm for one of those "wide" or ovalized looking ones, ~35mm toptube and 22mm for the back-end would probably not be far off.

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Cheers man. The bottom bracket is the main thing thats confusing me because i will have to put threads in myself so i need to allow for the thread depth when im tapping it but does that 33.5 include the thread depth? I read somewhere that its 24tpi but im not too sure how that relates to the depth if at all.

I think im going to try and use a 1"1/2 (39mm) tube for the downtube because otherwise it will be a pain to fit and get a nice weld on it

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Bb threads are 1.37"x24tpi. Don't forget the drive side is left hand thread. But as Dave says, Spanish would be better. If you get the dimensions any decent tool shop could knock you one up, it's just a stepped tube effectively

Edited by bing
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i didnt even know they sold them separately? But the first concern that comes into my head is then how it would weld up as the welds would be stronger if they were made from the exact same material


Bb threads are 1.37"x24tpi. Don't forget the drive side is left hand thread. But as Dave says, Spanish would be better. If you get the dimensions any decent tool shop could knock you one up, it's just a stepped tube effectively

oh i could probably make it up at work but i have no idea how they fit in haha

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Here is a suggestion. Go to any bike shop (including Hellfrauds), ask for one the scrapped frames (there will usually be a couple sitting in the metal bins). cut the head tube and bb off. Weld into your new frame.

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either way im still trying to find someone to tap the threads for me. ive messaged a few companies but they all said that they either dont have the taps or wont do it because they only use them for chasing the threads

Edited by Kenny--Trials
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It was bearing precession I was thinking of...

I don't know what stage you're at, but you could maybe just try buying some pre-built BB shells? Companies do sell ready-made parts like that which might help you out if you're struggling.

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