gxaustin wrote:Its quite straightforward to check frame alignment, using a piece of string....viewtopic.php?f=1&t=59332&hilit=string
That's neat. Is it true that the industry standard for misalignment on mass produced bikes is 2mm? E.g difference between head tube and a right angle from BB axis, Length from drop outs to BB axis.
When Chris Juden was CTC Technical Officer, he was involved in British Standards for aspects of bicycle construction, lighting, and so on. Various political machinations have swept away both the CTC as a members club, and any sort of pride in national identity, I wouldn't know where to look for information.
If you wanted to check that the BB axle was square to either the seat or top tube (so that when the bike was upright, the BB axle would be horizontal and square to direction of travel) I think you would need some big, accurate and expensive gear, like a big engineering-flat table, distance-pieces, squares, dial gauges….. There are a lot of dimensions on a frame which I can't think how I would set about checking. (In contrast, I can go into any builder's merchant and buy a laser level which will shoot a level line all round the room, but there is a consumer demand.)
If I was in a bike shop and required to check frames, I think I would have spacers made up so I could insert forks into the head tube without fitting a headset and then do my piece of string tests.
Looking at a drawing of a Spa bike (drawn in the Far East, on a computer of course) the only dimension which has tolerances attached is the dropout width, which is 135 [-0.0 +1.5] (ie. 135 to 136.5mm). Dropout width will be cold set after fabrication anyway.
Lots of stuff (tube lengths, angles) are quoted to one decimal place in millimetres or degrees, so I think the drawing is more precise than its actually possible to either measure or build.