A colt is a horse, but a horse isn't necessarily a colt. Get my drift?dbstoo wrote:Don't mean to beat a dead horse, but given the assertion "Observe proper tool geometry and pitch diameter and the other features will be correct" , does it not follow that you will reach the calculated depth if you observe proper tool geometry and pitch diameter? And given that, a tool with the proper geometry that cuts to the proper depth would also result in "the other features will be correct"?
No, it does not. That's due to the relaxed tolerance of less critical features, and is exacerbated by the fact that a minor change in tool tip width (still in tolerance) can equate to a large difference in pitch diameter. For example, if one works to the edge of tolerance for minor diameter (doesn't matter which edge), pretty good chance the pitch diameter will be wrong. It's simple. In a perfect world (show me one, as I've yet to find one), what you propose might work, but in reality, if you judge threads by major or minor diameters, pretty good chance pitch diameter wouldn't be correct. It may not matter in the home shop, but there are situations where it would matter, and a disservice is done to those who are not made aware.
Please note that I am not implying that it doesn't work. My point is, and has been, right along, that if you wish to create proper threads, you can not ignore the pitch diameter, which tends to have the tightest tolerance on thread forms.
On the subject of minor diameters--ever notice that the no go of a plug gauge has a truncated major diameter? It's sole purpose is to gauge pitch diameter (as well as lead, it goes without saying). The go gauge will gauge the major diameter, so it is important that the no go not be restricted from testing the pitch diameter. Rule of thumb, where I was trained, was that a loose thread could accept a no go by two turns, no more.
Harold