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Tech. Advice: Vincent/NSU Fox/Quickly Bikes
Metric/Imperial Threads
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<blockquote data-quote="Magnetoman" data-source="post: 140409" data-attributes="member: 2806"><p>Are you sure about that? Did you actually measure the profile with a microscope or comparator? It's actually pretty difficult to do with reasonable certainty with screws that small, and if you assumed that since it's metric it had 60 degrees it would have been very easy to think you saw 60 degrees.</p><p></p><p>It actually makes a lot of sense. Once the smooth progression of, say, drill bit sizes was decided on, having a machinist ask the tool room to give him a #47 bit is a lot less prone to error than asking for a "zero point zero seven eight five inch" bit. </p><p></p><p>As for BA fasteners, it makes excellent sense to have them in a geometric progression so it makes sense to number them by the power they're raised to rather than either some arbitrary number or their measured pitch. Since pitch = 1mm × 0.9^n the larger the BA number, the smaller the pitch. So, you devise a system where the machinist asks for a BA4, or asks for one with "thirty eight point four eight" tpi.</p></blockquote><p></p>
[QUOTE="Magnetoman, post: 140409, member: 2806"] Are you sure about that? Did you actually measure the profile with a microscope or comparator? It's actually pretty difficult to do with reasonable certainty with screws that small, and if you assumed that since it's metric it had 60 degrees it would have been very easy to think you saw 60 degrees. It actually makes a lot of sense. Once the smooth progression of, say, drill bit sizes was decided on, having a machinist ask the tool room to give him a #47 bit is a lot less prone to error than asking for a "zero point zero seven eight five inch" bit. As for BA fasteners, it makes excellent sense to have them in a geometric progression so it makes sense to number them by the power they're raised to rather than either some arbitrary number or their measured pitch. Since pitch = 1mm × 0.9^n the larger the BA number, the smaller the pitch. So, you devise a system where the machinist asks for a BA4, or asks for one with "thirty eight point four eight" tpi. [/QUOTE]
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Tech. Advice: Vincent/NSU Fox/Quickly Bikes
Metric/Imperial Threads
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