We've all bought bolts and nuts.
If you are like me, you don't think much about them.
You just want them to be long enough and thick enough to fasten
whatever needs to be fastened.
If you are like me you know about the common types of bolts and what
they are for - and you get by.
If you are like me, you probably never gave much consideration to the
threads on the bolts. They just came along with the bolts. You order
1/4-20's or 8-32's, or 3/8-16's but still don't think much about what
it all means.
I never did - until last Friday.
Last Friday I found out that we had a little bolt problem at work -
more accurately, we had a little thread problem.
The company that I work for, like many companies, orders stuff from
We buy metal parts from them.
This particular part has a weldnut on it that is intended to receive a
3/8-16 stem threaded stem for a caster.
If you are like me, you think that the guy on the other end, who is to
punch and tap the hole for this common caster stem, won't really need
much more of a description than that.
Damn - assumptions are wild and terrible things.
By the time I was done I had spent three hours searching on the
internet, resulting in going to Borders to buy Machinery's Handbook
(27th edition) ($85.00) (Type smaller than the Book Of The Month
Club version of the OED) and then reading for hours over the weekend,
simply to understand the most basic terminology.
"It ain't rocket science"
Damned near is.
By the time I got done trying to understand major and minor diameters,
pitch diameter, thread pitch, thread engagement, fit classes, the
negotiation between the British Standard and the American Standard to
resolve the argument over flat bottoms v. rounded, helical degree
standards, grade bolts and the effect on relief, why square section
threads are more efficient but don't work, why Acme is not somewhere
to buy food, how metric bolts vary from lesser standards, etc., etc.,
etc. - I was plumb wore out.
I finally did learn enough to be able to write to the Chinese engineer
guy in language that I hope is acceptable to him, which quoted a bunch
of standards, engineering tables, accepted tolerances, etc., etc.,
etc., - which ultimately came down to the fact that, "Your friggin'
hole is too big and your threads fit sloppy".
But I got a cool book out of the deal.
If you work with metal, take a look at the Machinery's Handbook.
You can sit that sucker by the can for the next twelve years and not
get through it all.
And it has some great stuff in it.
(watson - who thinks he now has a handle on why the engineering boys
at college didn't go out much on the weekends.)
Tom Watson - WoodDorker