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Why is the tolerance TIGHTER - but for only the GO gauge - when measuring a plated thread? I've been scratching my head over this one for a while. All the guides say "3A go gauge, 2a nogo" for plated parts, but don't say why! Thanks guys
Is this again one of those threads where the OP falls off the face of the Earth after asking a question?
The first reply was almost three weeks after the original post.Very well maybe.... You give him too much info he has to digest it first before he can reply.
Why is the tolerance TIGHTER - but for only the GO gauge - when measuring a plated thread? I've been scratching my head over this one for a while. All the guides say "3A go gauge, 2a nogo" for plated parts, but don't say why! Thanks guys
The Pre-Plating and After Plating table entries are identical.
True.IMO the most (only?) relevant tolerance is for the finished thread.
True.
WRT the linked reference...
Since the values in the two tables are identical it's hard to understand the intent.
- Leigh
Thank you, Gordon.Excuse the pun but I think someone or some committee has screwed up.
"hard to understand" is being very diplomatic
Might be interesting to compare the ASME B1.1 specfications with the old B.S. 84, 1940 which covers whitworth form threads and B.S. 1095, 1942 which covers metric threads.
Judging by the condensed versions in my Newnes Engineer's Manual, (second version, second printing, dated 1964) these had a pretty sane and comprehensible way of going about things. Even the calculations are reasonably slide rule / book of table friendly. All summarised by the simple statement that for every 0.0001" of plating thickness to be applied the nominal dimensions of whitworth threads must be reduced by 0.00086" and BA threads by 0.00098" if both parts are to be plated. Half that if only one part is plated. A table going from 0.0001 to 0.0015 plating thickness too. Nowt about metric tho' so you'd have to do the calculations which don't look tricky. I guess something had to give when squeezing into two pages.
Clearly putting all the dimensional changes onto the externally threaded part is not going to fly if the plating is really thick or you are dealing with galvanised components but it does indicate that a simple approach can suffice. Caxtons equivalent book has the information for galvanised things giving dimensional modifications for both external and internally threadec components but it will be a bear to find.
Far as I can see specificationn suffer from feature creep after the first two or three iterations. Probably 'cos the real engineers have to get back to proper work so the academics and folk who do meetings take over.
Clive
First noticed this thread now. I've never heard of the gauge type thread gauges you mention but I can give you some information on plated threads.
Plated can for example be galvanized, chromed etc. (plating that adds) or electro polishing (SS) that removes.
electropolishing is most definitely not "plating", or even a "coating" process. it is a (reductive) surface treatment.
hot dip galvanizing, while a coating process, is also not usually defined as "plating", just as painting is not plating.
plating is usually electroplating or a chemical precipitation/ reduction such as "electroless Nickel".
the thickness of a plating deposition is highly variable, (less so for the electroless nickel), depending on the "throw" characteristics of the solution and the parts/anode orientation, agitation, temperature etc.
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