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Thread: Buttress Thread
08-01-2012, 12:15 PM #1
Hey guys, I have a part that has come in for repair. The male part is being re made however the female is not. The thread on it is a buttress thread. The problem I'm having is 1, I have never cut a buttress thread before. I do have an insert for the pitch I need though. 2, The OD of the male thread is 2.671 with a 12 pitch. This is a very odd size. Can't tell if its worn or if thats normal(2-41/64?) 3, how do you measure a buttress thread? Can you still use wires? I measured the ID of the female and its measuring 2.6". Something doesn't seem right as that would only leave .0355 single thread depth? Seems small. All I have is the worn out broken male and the female. Nothing else.
08-01-2012, 12:43 PM #2
http://www.f-m-s.dk/1.02.pdf and let me know what each flank angle is.
You can easily measure an external buttress thread with wires and probably the easiest way to do it is by drawing it up (a single pitch) in CAD and "inserting" a diameter that just goes above the OD. It can also be calculated but is not easy. You can't do anything unless you know what each flank angle is.
If you let me know the two flank angles I can make a suggestion.
This might help too International Thread Standards
The OD of 2.671" could perhaps be 68mm. As the pitch is 12 TPI it seems an unusually fine thread for a buttress.
I don't know about other members but I need more information before I can help.
I'm not sure either if the sub forum you're using is also the best one for this subject. You might also want to post it in General.
08-01-2012, 01:07 PM #3
The first link you sent only shows one type of buttress thread. Am I missing something? Anyway it is a 45 degree and 7 degree flanks.
08-01-2012, 02:38 PM #4
If you have a set of thread wires try a couple and the one where the top of the wire is just above the thread OD is best.
I don't know your 45º / 7º buttress thread so do you have a pitch diamerter tolerance?
08-01-2012, 04:53 PM #5
ive recently thread buttress in MM it was something like M40x2.0 you can have buttress thread in metric in the gaz industrie so might take a look if its not in MM before you do anything else.
08-01-2012, 05:03 PM #6
After you determine what buttress thread angles you need, you also have to put them on the correct side of the part. You can flip a 60° threaded nut on either direction, but buttress threads only work one way.
Buttress threads are designated as 'push' or 'pull' threads and it is not always obvious what the part needs without referencing the print--especially then the buttress threads are in the middle of a shaft with no shoulder.
Look closely and make it once.
08-02-2012, 03:35 AM #7
Have a look at these links:
File:ANSI 45-7 Buttress thread form.svg - Wikipedia, the free encyclopedia
Buttress thread - Wikipedia, the free encyclopedia
15.2 Thread Standards
I'm not going to risk giving you incorrect information so I suggest you find out exactly which standard applies to the 7/45º Buttress thread you have and buy the standard.
ANSI B1.9 looks like a good possibility (the 3rd link I posted).
A suitable thread wire looks anywhere between 0.047 and 0.060" in diameter. It must have contact with both flanks and the top of the wire be above the OD.
08-02-2012, 03:46 AM #8
08-02-2012, 04:15 AM #9
Is there any way you can take a casting of the female thread, greasing and stuffing with car filler might work but don't forget to include a handle to screw it out with, and find out exactly what you have in there? Buttress threads are generally load pushing devices and the shape means that strength goes down dramatically with serious wear. If the male is worn female should be pretty bad too. Guy I used to know who occasionally did this sort of work always refused point blank to make individual male or female repair parts for this reason. You wanted a repair, you got a mating pair. He kept a worn male and part sectioned female around as a show'n tell awful warning! Think he just made to nearest standard size, never bothered to replicate OE as there are some right weird variations out there especially on old stuff.
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08-02-2012, 07:41 AM #10
08-02-2012, 09:23 AM #11
The female part is steel, the male part is aluminum. It is definitely not a metric thread. It is indeed a 12 pitch. The male shows clearly which way it the force is. This is a hydraulic unit. Its for a mobile crane. I am getting the insert tomorrow.
Now for measuring, I did this. The customer said its not the thread that is worn, but the part where the seal is (leaking). So I put the part in the machine, used .045 wire, took the OD measurement and am going to make the new thread to match. This too hillbilly like? The fit on the thread right now is still really good. Its other parts of the male that are worn out.
08-02-2012, 12:32 PM #12
08-07-2012, 07:22 AM #13
Got er done. Just copied the threads best I could and everything else fell right into place. Thanks for the suggestions fellas.