IVA... nuts and bolts...
Discussion
ColinM50 said:
Three threads showing is just good engineering practice,
And two threads, or even one, isn't?Why? It seems to me that if extra thread is needed to retain the nut as it starts to unwind then there is a problem there anyway (inasmuch as it's not supposed to unwind at all).
Well singlecoil, you can't always ask why, sometimes things just ARE.
I remember from my apprenticeship that 3 threads showing was the accepted method. Admittedly that was a few years ago, but it's sort of stuck in my mind. Along with stuff like opposite over adjacent = tan. Dunno why that is or what use it is either or when I'd ever use it, never have since I left school in nineteen hundred and frozen to death, but it's stuck in my mind all these years
But I guess in reality you're right. Why not one or two? Maybe 'cos if it comes undone a bit, you've got more time to spot it if it's got to undo three turns (plus the depth of the nut) before dropping off? In which case of course make it four or five threads but I suppose you've got to draw the line somewhere.
Dunno, as I said at the start, sometines things just ARE, but if you want to see the maths behind it I'm sure tyou can do a search on the web and find a better explanation. And then come to the decision that "three threads showing is good".
I remember from my apprenticeship that 3 threads showing was the accepted method. Admittedly that was a few years ago, but it's sort of stuck in my mind. Along with stuff like opposite over adjacent = tan. Dunno why that is or what use it is either or when I'd ever use it, never have since I left school in nineteen hundred and frozen to death, but it's stuck in my mind all these years
But I guess in reality you're right. Why not one or two? Maybe 'cos if it comes undone a bit, you've got more time to spot it if it's got to undo three turns (plus the depth of the nut) before dropping off? In which case of course make it four or five threads but I suppose you've got to draw the line somewhere.
Dunno, as I said at the start, sometines things just ARE, but if you want to see the maths behind it I'm sure tyou can do a search on the web and find a better explanation. And then come to the decision that "three threads showing is good".
ColinM50 said:
Well singlecoil, you can't always ask why, sometimes things just ARE.
I remember from my apprenticeship that 3 threads showing was the accepted method. Admittedly that was a few years ago, but it's sort of stuck in my mind. Along with stuff like opposite over adjacent = tan. Dunno why that is or what use it is either or when I'd ever use it, never have since I left school in nineteen hundred and frozen to death, but it's stuck in my mind all these years
But I guess in reality you're right. Why not one or two? Maybe 'cos if it comes undone a bit, you've got more time to spot it if it's got to undo three turns (plus the depth of the nut) before dropping off? In which case of course make it four or five threads but I suppose you've got to draw the line somewhere.
Dunno, as I said at the start, sometines things just ARE, but if you want to see the maths behind it I'm sure tyou can do a search on the web and find a better explanation. And then come to the decision that "three threads showing is good".
I think that if you want to use maths to prove your argument, then you should do the search. I'm guessing that you are going to have to do a lot of searching, though, and even then your chances aren't very good.I remember from my apprenticeship that 3 threads showing was the accepted method. Admittedly that was a few years ago, but it's sort of stuck in my mind. Along with stuff like opposite over adjacent = tan. Dunno why that is or what use it is either or when I'd ever use it, never have since I left school in nineteen hundred and frozen to death, but it's stuck in my mind all these years
But I guess in reality you're right. Why not one or two? Maybe 'cos if it comes undone a bit, you've got more time to spot it if it's got to undo three turns (plus the depth of the nut) before dropping off? In which case of course make it four or five threads but I suppose you've got to draw the line somewhere.
Dunno, as I said at the start, sometines things just ARE, but if you want to see the maths behind it I'm sure tyou can do a search on the web and find a better explanation. And then come to the decision that "three threads showing is good".
And you can always ask why.
Edited by singlecoil on Wednesday 21st April 15:14
If it works on ships it must be pretty accurate for most other things.. Basically says 1 thread showing beyond nut or nylock part of nut is sufficient.. I think the reason behind having threads showing is so you know the threads are fully engaged.
If I was going to build something and someone said it needed to be 3 threads I'd make sure it was, it's going to be very time consuming changing them all.. That and as someone else said if you know you did them all at 3 threads minimum and one day you notice no threads showing on one you know there's a problem.
Naval Ships' Technical Manual Chapter 075
Fasteners
Quote:
075-7.5 LENGTH OF THREAD PROTRUSION
075-7.5.1 MINIMUM THREAD PROTRUSION.
A minimum thread protrusion length is given to ensure that
all the threads are engaged. This is required to ensure a full-strength fastener. Equipment component drawings should specify the type, length, and size of bolt, stud, bolt-stud, etc. to be used to obtain the proper thread protrusion. If not specified on the drawings, threaded fasteners of commercially stocked lengths should be used. Threaded fasteners, when installed and tightened, should protrude a distance of at least one thread beyond the top of the nut or plastic insert. Excessive protrusion should be avoided, particularly when necessary clearances, accessibility, and safety are important. Thread protrusion is considered excessive if it could cause damage to machinery or harm to personnel. Where practicable, the number of threads protruding should not exceed five. In no case should thread protrusion exceed ten threads. In the case of a stud, excessive thread protrusion may indicate that the stud has not been properly driven in the blind hole. In self-locking nuts where the distance from the top of the nut to the locking element (plastic insert) is equal to or greater than the chamfer, the bolt or stud end may be flush with the top of the nut. For existing or reused fasteners where the thread protrusion exceeds 10 threads, verification should be made that the proper length fastener was installed. For existing installations utilizing standard nuts, acceptable minimum thread protrusion would be where the male thread, below any unthreaded chamfer or crown, is flush with the top of the nut. Washers should not be added to reduce protrusion except as specifically required by equipment component drawings or technical manuals.
075-7.5.2 MAXIMUM THREAD PROTRUSION.
There is no maximum thread protrusion from the standpoint
of the function of the fastener. Obviously, too much is a waste of material and weight. There is also a safety problem from long, sharp, threaded rods sticking out from equipment, and protruding threads can get in the way of other parts of the equipment. A good rule to follow is to always use the shortest standard length fastener that gives a minimum one thread protrusion. Small and/or short bolts come in 1/8- or 1/4-inch increments. As the fastener gets larger and longer the increments change to 1/2 inch. Up to a five-thread protrusion from a fastener is certainly reasonable, you shouldn't take a hacksaw to it for that; but if you have ten or more threads, you could probably have done a better job of selecting the length. There is no requirement to reduce the length of protrusion of existing fasteners before reinstalling them. There is also no reason you cannot cut off excess protrusion if it is obviously too long or in the way. However, you cannot use washers solely to reduce thread protrusion.
As far as closed wheel nuts, arn't nuts "normally" the same thickness as the diameter of the bolt shaft? From what I've seen they normally are.. So if the stud on a car wheel is M12 as long as the thread goes into the nut by atleast 13mm your ok.. This could be measured quite easily by an inspector after removing one wheel nut during the test. I think the reason for most of them to be closed is so they don't seize on after 5 mins on the road, and again I'm sure the SVA/IVA would appreciate that..
Feel free to correct me on any of that if I'm wrong :-)
Jim
If I was going to build something and someone said it needed to be 3 threads I'd make sure it was, it's going to be very time consuming changing them all.. That and as someone else said if you know you did them all at 3 threads minimum and one day you notice no threads showing on one you know there's a problem.
Naval Ships' Technical Manual Chapter 075
Fasteners
Quote:
075-7.5 LENGTH OF THREAD PROTRUSION
075-7.5.1 MINIMUM THREAD PROTRUSION.
A minimum thread protrusion length is given to ensure that
all the threads are engaged. This is required to ensure a full-strength fastener. Equipment component drawings should specify the type, length, and size of bolt, stud, bolt-stud, etc. to be used to obtain the proper thread protrusion. If not specified on the drawings, threaded fasteners of commercially stocked lengths should be used. Threaded fasteners, when installed and tightened, should protrude a distance of at least one thread beyond the top of the nut or plastic insert. Excessive protrusion should be avoided, particularly when necessary clearances, accessibility, and safety are important. Thread protrusion is considered excessive if it could cause damage to machinery or harm to personnel. Where practicable, the number of threads protruding should not exceed five. In no case should thread protrusion exceed ten threads. In the case of a stud, excessive thread protrusion may indicate that the stud has not been properly driven in the blind hole. In self-locking nuts where the distance from the top of the nut to the locking element (plastic insert) is equal to or greater than the chamfer, the bolt or stud end may be flush with the top of the nut. For existing or reused fasteners where the thread protrusion exceeds 10 threads, verification should be made that the proper length fastener was installed. For existing installations utilizing standard nuts, acceptable minimum thread protrusion would be where the male thread, below any unthreaded chamfer or crown, is flush with the top of the nut. Washers should not be added to reduce protrusion except as specifically required by equipment component drawings or technical manuals.
075-7.5.2 MAXIMUM THREAD PROTRUSION.
There is no maximum thread protrusion from the standpoint
of the function of the fastener. Obviously, too much is a waste of material and weight. There is also a safety problem from long, sharp, threaded rods sticking out from equipment, and protruding threads can get in the way of other parts of the equipment. A good rule to follow is to always use the shortest standard length fastener that gives a minimum one thread protrusion. Small and/or short bolts come in 1/8- or 1/4-inch increments. As the fastener gets larger and longer the increments change to 1/2 inch. Up to a five-thread protrusion from a fastener is certainly reasonable, you shouldn't take a hacksaw to it for that; but if you have ten or more threads, you could probably have done a better job of selecting the length. There is no requirement to reduce the length of protrusion of existing fasteners before reinstalling them. There is also no reason you cannot cut off excess protrusion if it is obviously too long or in the way. However, you cannot use washers solely to reduce thread protrusion.
As far as closed wheel nuts, arn't nuts "normally" the same thickness as the diameter of the bolt shaft? From what I've seen they normally are.. So if the stud on a car wheel is M12 as long as the thread goes into the nut by atleast 13mm your ok.. This could be measured quite easily by an inspector after removing one wheel nut during the test. I think the reason for most of them to be closed is so they don't seize on after 5 mins on the road, and again I'm sure the SVA/IVA would appreciate that..
Feel free to correct me on any of that if I'm wrong :-)
Jim
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