This is great i was sending a reply full of clever witticisms when ‘scheduled maintenance’ hit.Now I can’t do a point by point. I mean the other postings aren’t even here below this form. happening to any body else?
Any way, I think I know. At first I thought it had something to do with screw cutting lathes.The power head on a lathe is on the left to accomidate us righties. They turn top down toward you .( If somebody starts a thread about woodworking acidents I’ll tell you about the exciting whapped in the face by a mesquite log adventure and you’ll know why thet turn down) Anyway, I thought that it was a natural movement to move the cutter away from the head. Guess what? That makes a reverse thread. Then I had the BOING!
Hand tapping. They didn’t have lathes WAY back then. They cut threads by hand.The tap is a T handled affair. If you are tapping inside threads ( the nut [no comments now])the tap sticks down, if you are making a screw the tap is a hole in the middle of the handle with hard teeth set at an angle. You slip it over the free end of the screw.Now when you are tapping you turn it… clockwise. I don’t know about all righties but I have more control over force and precision when I PULL with my right hand rather than push. ( there is a posting about batting somewhere and they go into that in great detail) That makes a screw with a right hand thread. So that is my take on it for now. OH DANG! I just thought, what if the teeth were angle the OTHER way. Shoot! is there an aesthetic reason? Or maybe cutting the teeth in the tap is easier away and to the right?
Well, now, if you’re going to invoke all those things you learned in school, how about this?:
The Coriolis force affecting the direction of vortices in the Northern Hemisphere – like where Egypt is, which location is claimed in a post above to be the place where screwings first regularly took place (although I suspect it was really somewhat further south). 
You think those sons o’ pharoahs saw those vortices going toward the center of the earth (being north of the equator) and figured that perverted nails would only be so similarly groovy?
Well, I think the name of the game around this forum is to make up a reason when you can’t find one. Certainly, all those conventions of physicists and engineers came as a result of the right-hand screw’s predominating. The right-hand screw is probably only the result of ancient Egyptians (or whoever really first became helically biased)'s being mostly right-handed, and I think it’s a lot more natural, for a right-handed person to twist clockwise, and no doubt, such persons can more easily produce a large torque in that direction. You would figure that most people never hang around to take the screws out again, and anyway, in the case of no pre-threading, it requires much more torque to put screws in than to take them out.
BTW, if there are any auto mechanics tuned in, I once had the front disc brakes on my MGA fixed by a brake mechanic. The hubs have opposite threads on the two sides. . . You got it. At 55 mph on the freeway, I suddenly had three wheels and one fixed disk and ended up in the center divider. If you insist on having a British car, be sure you check out whether your mechanic’s brain hemispheres are properly polarized.
Ray (Right-handed – and, hey, I’m just an electronic engineer; I don’t screw around. But in Berkeley, here, you seemed to get screwed to the left.)
TWO PAGES? Goll durn it if I put both hands on a great long wrench (lever) and hang from it, it don’t matter if I got it on the left or the right side! Its getting ALL mt torque. And this new deal after “scheduled maintenance” has got me torqued! I hope they remembered to retighten(clockwise) the oil drain plug, I don’t even wanta think about the brakes. There is someother stuff i could say but I can’t see the postings.
Cornflakes said:
Isaac Asimov wrote an article quite a few years ago that he called “The Left Hand of the Electron”, later collected in a book of the same name. He cites some research that seemed to show that electron spin is biased, and suggests that this might explain why proteins (and screws and people!) exhibit handedness.
Bob the Random Expert
“If we don’t have the answer, we’ll make one up.”
F X r != r X F ?
I feel I must have missed something here. Could you please explain the major difference to those of us who still believe in the commutative property of multiplication?
Astroglide, the ‘X’ in this case refers to a cross-product of vectors. The answer gives you a magnitude and a direction. r X F and F X r have the same magnitude, but opposite directions.
Ok so now I know why my electric screw driver works so well. except when I am working over my head then it screws up.
Signitorily yours, Mr John
" Pardon me while I have a strange interlude."-Marx
So why not keep the nut threaded normally and have the fan blades go in reverse?
Have the fan blades go in reverse?
Alpha,I think this has to do with that electromagical stuff they are talking about.
{{{I can’t believe no one has yet pounced on Strainger’s remark that Mr. John’s brain is difficult to describe verbally. wink}}}—Chef Troy
Actually, I was thinking of pouncing on this:
{{{And, yes, I apply the right hand rule at work.}}}—Strainger
But I won’t . G
{{{So why not keep the nut threaded normally and have the fan blades go in reverse?}}}---Alphagene
As an aside: Because that would suck.
So much for lurking!
------------------
--**Kalél**
(The Original **EnigmaOne**)well, corn, you started this thread about threads. Now look how flakey it’s become.
The obvious answer is because it’s the only right way to do it, as any right wingnut will tell you.
Signitorily yours, Mr John
" Pardon me while I have a strange interlude."-Marx
Well, none of the above explains why drill bits drill clockwise. And what about the corn borer. Does it bore clockwise or counterclockwise? And which way did the Egyptians make their animals turn their water pumps and why?
Maybe all these things depend on which way the earth is spinning. It did change a few times, didn’t it?
Ray (wouldn’t be this corny if I weren’t so bored)
::Kicking myself in the ass as I type this::
I was at the used book store this weekend (the books, not the store, were used), and decided to find out what I could about screws. To summarize (from memory, so cut me a little slack):
- Although they did exist some time earlier, the use of screws didn’t really take off until the invention of Archimedes’ screw.
- There were no standards regarding pitch, size, etc. until early in this century (or maybe it was late last century).
I wasn’t able to find anything about right-handed threads until I pulled out one of my textbooks here at work. The answer was about 2 feet away from me the whole time. From Mechanical Engineering Design by Shigley and Mischke:
It doesn’t require a giant leap in logic to associate the right-hand rule with right-handed threads.
I’d still have to draw it out to see if it were so (too lazy right now) but if it WERE so, the difference between a righthanded screw and lefthanded screw WRT mechanical advantage due to torque differences is MINISCULE… As r->0, T->0 so for the radius of a screw, torque should be damn close to nil within experimental error for any reasonably small F, such as one that could be exerted by the average human hand. It is doubtful that the ancients, in designing the screw, noticed any difference. Also, I believe, since force is applied equally to points equidistant along a line perpendicular to the axis of the screw, net T=0, but this could be bullshit. So even if the righthanded screw DOES obey the righthanded torque rule (and I have not been convinced that it is necessarily related) it does not make enough of a difference to be measured.
Jason R Remy
“Open mindedness is not the same thing as empty mindedness.”
– John Dewey Democracy and Education (1916)
Sorry, but the direction of the “torque vector” is just a mathematical convention for expressing a torque in vector form. A left-hand rule could have been decided on just as easily. It’s like deciding on which way is +i and which way is -i.
If there is any reason at all for right-handed screws (other than convention) it has to do with right-handed humans using tools.
John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams
Am I ever going to get through to you people? I presented evidence as to why they’re called right-handed threads and why they’re threaded that way (SO THAT THEY’LL FOLLOW THE RIGHT-HAND RULE FOR CHRIST SAKE!!!). In doing so, I used a textbook that is a standard among mechanical engineers, and yet y’all still choose to ignore it.
jayron:
Jayron, if you turn a right-hand threaded bolt clockwise, it tightens. If you turn a left-handed threaded bolt clockwise, it loosens. This is not a minscule difference.
If it’s a right-handed screw, then it follows the right-handed rule by definition.
Look, I’m a mechanical engineer. I use the right-hand rule frequently (not to be confused with the right-hand method) to calculate direction of torques (e.g. on bolts), moments in structures, etc. I am quite familiar with theory behind bolts, nuts, etc. I suggest paying attention to the evidence I presented rather than following your own wild-ass guesses and speculations.
Ignore my response to the first quote, jayron. Upon rereading, I realize that I misinterpreted that statement earlier.
OK… Strainger, I think by your second post you may have gotten my point, but I’ll restate it for those that don’t:
A screw threaded so that a clockwise turn tightens it offers no mechanical advantage over a screw threaded so that a counterclockwise turn tightens it. Thanks to those who have pointed out that the direction of the torque vector is an arbitrary convention and in no way indicates a mechanical advantage of turning something one way or another…
But even if it did, the difference would be so miniscule as to be immeasurable at the level of a screw turning.
Thus, either way it is an arbitrary convention that we have one kind of screw over another. As is the case with most of these things, a convention IS important to have, but WHICH convention is unimportant.
Jason R Remy
“Open mindedness is not the same thing as empty mindedness.”
– John Dewey Democracy and Education (1916)
John W. Kennedy’s last post is exactly right. . .and is basically only common sense. Jayron 32’s post says essentially the same thing.
Strainger apparently bases his mystical thinking on the fact that he is a mechanical engineer. As an electronics engineer, I have run into some of the ways mechanical engineers think. . .or not, as the case may be. In fact, every time I work on my car, I find that cars are incompatible with common sense, apparently for that reason.
Ray (pretty torqued down)
Nanobyte, don’t tell me my business. You obviously don’t have a clue about any theories behind mechanical engineering.
I will now summarize:
Q: Why are most bolts and screws threaded in the same direction?
A: Because there needs to be a standard.
Q: Why are these standard bolts threaded so that they tighten when turned counterclockwise and loosen when turned clockwise?
A: Because this is the direction of the resultant torque vector as calculated by taking the cross-product T = r X F, where ‘r’ is the distance vector (location of the applied force) and ‘F’ is the force vector. The direction of the resultant cross-product (torque, in this case) is determined by applying the right-hand rule.
Q: Why are bolts threaded this way called right-hand threads?
A: Because they follow the right-hand rule. Duh.
Don’t believe me? Check the source (Mechanical Engineering Design by Shigley and Mischke) I quoted earlier. It will verify the information I’ve given here.
You must own a Grand Am.