Can anybody explain the difference between Effective Diameter - as used on British Standard threads - and Pitch Diameter - as used on ISO and ANSI threads ?
I know how Pitch diameter is defined, concentric to thread and H/4 further from the root, where H is the height of the fundamental angle.
I believe the effective diameter is at the point where the width of the metal of the thread equals the width of the valleys between threads. Assuming a regular thread form, this would, I suppose, be half way up.
Wilfrid Underwood
Quote:
"Effective diameter of a parallel thread is the diameter of the imaginary coaxial cylinder which intersects the surface of the thread in such a manner that the intercept on a generator of the cylinder, between the points where it meets the opposite flanks of the thread groove is equal to half the nominal pitch of the thread"
From "Engineering Workshop Data", Arthur W Judge, Caxton, 1951.
If I get a minute I'll post a picture that makes this a little clearer.
Peter
Lionel
Lionel
I'd like to thank everybody for theirhelp and assistance.
I'm still ofthe belief that Pitch Dia. & Effective Dia. are different definitions, but with ISO, ANSI & BS threads they are the same measurement, ie, if root & crest radii are different on BS threads or if the root is changed on a ISO or ANSI thread they would be different measurements.
The reason I asked for this info is because I use Autodesk Inventor, which has thread definitions defined in a spreadsheet. At the moment BS thread aren't defined. I've used Machinery's Handbook v26, but I can't find any way to calculate the minimum Major Diameter, the minimum Pitch/Effective diameter and the minimum Minor Diameter of BS bolts nor can I find any of the dimensions for BS nuts.
The equations given in M.H.v26 become circular ! ! !
The dimensons i need are, External Class, Max-Major Dia, Min-Major Dia, Max-Pitch Dia, Min-Pitch Dia, Max-Minor Dia Internal Class, Min-Minor Dia, Max-Minor Dia, Min-Pitch Dia, Max-Pitch Dia, Min-Major Dia, Tap Drill Dia.
TIA Duncan Anderson
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