Originally Posted by
Nic Scheepers
... I am a newbie to the world of twisting and turning metal......
......I now thread the inside of this nut. Guess what? the nut is way too small for my bolt. I know a lot of you may laugh but this is really frustrating to me....
Not only are you twisting and turning metal you are also bending it, elastically so it springs back. Tool deflection or workpiece deflection it is called. You might move the tool in to take a cut .005mm deep but really it cuts slightly shallower than that. On the two, intended to be mating, parts with such a fine thread the 'slightlys' can add up to be significant compared with the actual dimensions.
Don't let the book theory dictate to you let it guide you. You figured out the theoretical starting dimensions and thread depth but things did not fit. Add or subtract a tiny allowance for tool deflection; make your bolt thread a bit smaller and nut a bit larger. With experience you will find that after a while you can make a darn good guess the first time and come up with parts that fit nicely first try.
Even with years of experience and really fancy equipment cutting a thread from scratch to theoretical dimensions and getting it to fit perfectly the first time is as much a matter of luck as it is skill; and the phase of the moon and how may ladders you walked under last week . Even when things are running just fine you can get tripped up because you use a piece of 'identical' steel from a different bar and the properties are within spec but just different enough that the tool deflects differently.
Which is why you always check the part before taking it out of the machine and losing your alignment.
An open mind is a virtue...so long as all the common sense has not leaked out.