Re: odd thread
- This is a buttress thread. One use is on the back end of a Mauser rifle bolt. The entire firing pin/cocking assembly screws into the back of the bolt body on a buttress thread. All the force in this assembly is in one direction, with the load provided by the mainspring. Very strong in one direction, not so much in the other (but not needed).There are specs for some of these threads in Machinery's Handbook IIRC.Jim (Just a guy who likes to build stuff)
- I cut a lot of buttress threads before I retired.
My first encounter with the design was when I was repairing hydraulic cylinders for Bobcats. Since the tubing is thin walled, using a buttress thread helped to not exert force outward, thereby expanding the thread fit. Also, it was said that the thread stood up better to the constant hammering from the full extension of the cylinder.
The thread actually has a 45° flank, and a 7° flank that took the load.
Our company purchased insert tooling to make it more efficient time-wise.
The thing I had to get in my head was to use opposite ground tool bits for internal and external threads.
The next odd thing is that like all machinists, I would take small cuts and "sneak up" on a very nice fit. With buttress threads, when you test fit, and it wont go, you take .003" more, and it feels too loose. But it isn't too loose, that is the nature of it.
Larry in WV
--- In firstname.lastname@example.org, Jerry Durand <jdurand@...> wrote:
> Looking through an old book I have on machinery it shows several
> different threads. One is trapezoidal, instead of say 60 degrees on
> both faces, one is 90 degrees and the other is 45 degrees. Any idea
> what this would be for?
> Jerry Durand, Durand Interstellar, Inc. www.interstellar.com
> tel: +1 408 356-3886, USA toll free: 1 866 356-3886
> Skype: jerrydurand
- This also looks like the type of thread used on PVC/CPVC pipe unions.
--- In email@example.com, Arthur Marks <arthur.marks@...> wrote:
> As already mentioned, that is called a "buttress" thread. Here is a
> smaller example I've cut... http://tinyurl.com/ayorxna Some collets use
> such a form for their drawbar threads. There are subtle different types,
> though, worth noting. For example: 45-7 degree, 45-5 degree, 45-0 (as you
> mention). You can find them in Machinery's Handbook; they haven't been
> retired to history. -Arthur
> On Wed, May 15, 2013 at 1:22 PM, Jerry Durand <jdurand@...>wrote:
> > Not Acme, right triangle. One face is 90 degrees from horizontal, the
> > other is 45 degrees.