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Author Topic: only for ENGINEERS  (Read 7473 times)

supersonic

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only for ENGINEERS
« on: October 28, 2007, 09:57:05 PM »

OK ENGINEERS !,Big discussion tonight at the pub, regarding bolts and screws and the difference between the two
I maintain that a scew can only be tightened by its head.

A bolt cannot be tightened by its head. ( eg. coach bolt )
A coach screw can be tightened by its head

A bolt requires a nut to be tightened

A hexegon head screw tightened with a nut therefore becomes a bolt !

Engineers only reply !

sorry for this post but this has got my back up

Come on lads lets get it sorted.

Dave.
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Supersonics Son

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Re: only for ENGINEERS
« Reply #1 on: October 28, 2007, 10:01:14 PM »

Ha ha ha,,, Funny this one... Forgotten the full problem but the landlord did say nthat a screw has a point and a bolt dont.... But then the landlord has never had a point...lol

So if a screw has a point why does a a coach bolt have a point also why does supersonic post this on a thread....lol.... Beat ya to it dad......

Come on I see a big debate coming on here and a fun one..... ;D
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supersonic

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Re: only for ENGINEERS
« Reply #2 on: October 28, 2007, 10:07:19 PM »

What do do landlords know about engineering  ?

This post was specifically for ENGINEERS !

Dave.
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Tug-Kenny

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Re: only for ENGINEERS
« Reply #3 on: October 28, 2007, 10:12:15 PM »


Only my opinion,  but a screw has a cutting thread,  whereas a bolt has a dull edge on its thread ready for the NUT.   :)

Cheers...Ken


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RMH

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Re: only for ENGINEERS
« Reply #4 on: October 28, 2007, 10:14:14 PM »

I was taught that a bolt has an unthreaded portion of shaft, the thread of a screw runs right up to underneath the head
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djrobbo

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Re: only for ENGINEERS
« Reply #5 on: October 28, 2007, 10:14:37 PM »

Hi gys.....i was always told that anything with a slot for tightening up or undoing (cross or straight ) was a screw a bolt had either a square or hexagonal head to be tightened with a spanner or socket.......but i have to admit that i was never exactly certain


                     regards..bob..
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Supersonics Son

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Re: only for ENGINEERS
« Reply #6 on: October 28, 2007, 10:15:32 PM »

 :) Humm this is going to be a LONG THREAD.....lmao
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wombat

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Re: only for ENGINEERS
« Reply #7 on: October 28, 2007, 10:40:17 PM »

Differences between the two -

A bolt is a bolt, a screw is a screw - simple.

The differences are largely empirical in my mind.....

If it is above about M6, then by and large it is a bolt.
If it has a hex head then it is a bolt
If is is slotted, pozi or torx it is a screw.

Wom

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supersonic

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Re: only for ENGINEERS
« Reply #8 on: October 28, 2007, 10:48:54 PM »

Sorry Wombat -------- Totally wrong,
A coach bolt cannot be tightened by the head but a coach screw can, whatever the size  ! :)
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meridian

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Re: only for ENGINEERS
« Reply #9 on: October 28, 2007, 11:12:07 PM »

Generally, if it has a hexagon head it is a bolt, no matter what size it is. Screws are available in a variety of head configurations, i.e. countersunk head, round head etc. and with a range of slots, i.e. straight slot, pozi-drive, hexagon slot (the Allen screw)etc. That's the accepted convention. The exceptions are coach bolts which have plain low domed heads and coach screws which can either have a hexagon head or a square head!
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wombat

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Re: only for ENGINEERS
« Reply #10 on: October 28, 2007, 11:29:33 PM »

Sorry Wombat -------- Totally wrong,
A coach bolt cannot be tightened by the head but a coach screw can, whatever the size  ! :)

Actually not totally wrong - merely an incomplete list. The information that is there, I challenge you to find fault with it, if you cannot then it is not wrong. Unless there is nothing correct in it then it cannot be totally wrong.

Part of the problem here is that you are crossing disciplines - Coach-screws/coach bolts are for woodworking, where the difference is that the screw cuts its own thread while the bolt is passed through a clearence hole and retained with a nut. But by this definition a machine screw is not a screw but a bolt, unless of course it is a tap-tite - but by popular usage it is a screw.

Wikipedia offers this definition of the difference between bolts and screws, which I think is what you are hinting at:

A bolt passes through a hole of larger diameter than its thread, and is held in place by a nut or similar device; it is not designed to be turned. What is often referred to as a bolt is in fact a cap screw, which is designed to be turned (or screwed). Cap screws may, or may not be used with nuts. The distinction is subtle, but significant in the design of the fastener. If threaded all the way to the back of the head a cap screw becomes a machine screw.

This, though, is a flawed definition because there are cases where the definition of what is a bolt or a screw depends on how it is used - by this definition, if I pass an item through a clearance hole and lock with a nut then it is a bolt, but if I fasten the identical object into a threaded hole it is a screw.

I suspect any rigorous attempt at a definition will end up in problems.
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Colin Bishop

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Re: only for ENGINEERS
« Reply #11 on: October 28, 2007, 11:48:27 PM »

I always thought that a bolt was what you did if you inadvertently put a screw in the wrong socket. But then I'm not an engineer.....
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RickF

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Re: only for ENGINEERS
« Reply #12 on: October 29, 2007, 12:52:54 AM »

I am reminded of the newspaper report that appeared after a lunatic broke into the asylum laundry, raped several of the workers and then escaped. The headlines read..... (wait for it!)....

NUT SCREWS WASHERS AND BOLTS

Rick

PS I have to agree with the earlier definition - I was taught that bolts have an unthreaded portion of shank, machine screws are threaded up to the head.
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wombat

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Re: only for ENGINEERS
« Reply #13 on: October 29, 2007, 08:48:22 AM »

From a site where the author is bitching about sloppy definitions from "credible" authorities

Quote
Having "credible" sources such as Machinery's Handbook, ASME, ISO, and military specification sheets misusing and arbitrarily misdefining the words throws the whole world off.

They give the definition of a bolt as:

Quote
Bolts are defined as headed fasteners having external threads that meet an exacting, uniform bolt thread specification (such as M, MJ, UN, UNR, and UNJ) such that they can accept a nontapered nut.  Screws are defined as headed, externally-threaded fasteners that do not meet the above definition of bolts.

So by their definition a bolt is a bolt if it is made to a bolt standard otherwise it is a screw.

http://euler9.tripod.com/bolt-database/boltdef.html

By and large it seems to me that the distinction between a bolt and a screw is largely arbitrary - we can agree at the extremes - we konw what a bolt is and we know what a screw is, but where you transition from it being a bolt to it being a screw is largely a matter of common usage. For instance Rick comments

Quote
PS I have to agree with the earlier definition - I was taught that bolts have an unthreaded portion of shank, machine screws are threaded up to the head.

I thought these were "shanked bolts"
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bogstandard

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Re: only for ENGINEERS
« Reply #14 on: October 29, 2007, 10:23:38 AM »

If you go into a reputable engineering supplier and ask for a low tensile, hex head (or any other shaped standard head), 1/4" BSF, 3" long screw, you will be supplied with a screw that is threaded to just underneath the head, if on the otherhand you ask for a bolt, you will be given a bolt that has a plain portion under the head with a standard length of thread on the bottom end (varies with diameter and type) but on this size would be about 1" long.

John
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meridian

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Re: only for ENGINEERS
« Reply #15 on: October 29, 2007, 10:35:35 AM »

Machine screws usually have a minimum thread length according to the relevant standard. This can be dependant on nominal thread diameter or length of screw (shank). For instance metric machine screws up to M1.4 and screws of larger diameters that are too short for the specified minimum thread lengths, are threaded as far as possible up to the head. All other machine screws are normally supplied with shanks that have an unthreaded portion.
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chingdevil

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Re: only for ENGINEERS
« Reply #16 on: October 29, 2007, 11:07:14 AM »

Engineering Bolts do not have their thread all the way to the top but have a plain shank (I can not remember thr formula to work it out)
Engineering Set Screws have the thread all the way to the top

I deliberately did not say what the top would be as you can get both hex head and allen head bolts the same with set screws. You can also get specialised bolts and set screws that have a slot or crosspoint.

Coach bolts and coach screws follow the same rules as above, with the exception of slots and cross point heads. I have never understood why a wood screw is called that when it can have a plain shank or threads all the way to the top ???

Brian
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RickF

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Re: only for ENGINEERS
« Reply #17 on: October 29, 2007, 11:43:54 AM »

Left to itself, this one will run for ever!

When Whitworth sat down in the 1840s and devised a standard for "threaded fasteners", his main aim was to make the things interchangeable, so that Joe the village blacksmith could go down to his B&Q (or whatever they had then) and buy some "threaded fasteners" which he knew would fit the Squire's traction engine when it came in for repairs. Whether he called them bolts or screws is immaterial and academic - he knew what he wanted and his only concern was that they would fit the job in hand.

Over the years other standards and designs have come along. Metric, ISO, Unified and many more. The hexagon head has been joined by slotted, cross-head, Allen and no end of others. Definitions have come and gone too, and common usage has blurred what was probably once an easily-described item of hardware. For instace, all bolts have screw threads. You screw a nut onto a bolt.

Whatever definition we now use for "threaded fasteners", someone will come up with an exception to prove it wrong. It makes for an entertaining discussion on the forum, but in the end we are just like Joe the blacksmith - we know what we need for the job, and as long as what we get fits, it really doesn't matter what its called.

Rick
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polaris

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Re: only for ENGINEERS
« Reply #18 on: October 29, 2007, 12:38:02 PM »


Dear All,

Rick, I completely agree with what you say.

May I add something just for the benefit of others who possibly might not know - which will be very few I know. The purpose of the unthreaded shank on engineering bolts, is quite simply to ensure the smoothest and tightest fit between the metal being joined. Should the metal being 'joined' be under stress/vibration from any direction, wear to both thread/bolt and hole will result if the joins be in contact with the threaded part of the bolt - thus slackness in any assembly will likely result - and things can start moving with expensive consequences! The same applies to non-engineering bolts, as wood, plastic, etc. will obviously wear in the same way. Thus washers are used to raise the nut to the level of the thread above the level of the metal or wood being joined. Obviously, if any material being joined is threaded right through then obviously full contact results and there is no problem. Most of our modelling applications are more tolerant of course, but, with motors other than elec. it might be wise to conform with the status quo - I am only familiar with elec. myself, and have no knowledge of other modelling power sources. I know all this is very basic but it is intended only to be a very brief descrip. of possible interest to one or two who might not know.

This is also not intended to start a long conv. on bolt usage/application! - I don't want the blame for instigating same under this Topic! :)

Regards, Bernard
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Colin Bishop

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Re: only for ENGINEERS
« Reply #19 on: October 29, 2007, 12:44:56 PM »

Actually, I'm finding it quite interesting. Some good explanations on a subject that a lot of us have probably never really thought about. Whitworth did a good job considering just how much his system is still used today.
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Captain Povey

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Re: only for ENGINEERS
« Reply #20 on: October 29, 2007, 12:56:11 PM »

Hi all, I think I already gave my definition in another thread and I agree with the previous simple definition. Screws have the thread along the whole length, bolts are threaded for only a proportion of the length. Graham, C Eng  O0
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Circlip

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Re: only for ENGINEERS
« Reply #21 on: October 29, 2007, 01:08:12 PM »

 
   You're a technological Luddite Colin, NO such thing as Whitworth anymore, everybody in the world (except the
   descendants of the Pilgrim fathers on t'other side of pond ) changed to Proper sizes in late 60's.  We got them
    out of the excreta in the 40's but they still dumped on us in the 60's . 
     Machine screws change sex to become Bolts beyond a length to diameter ratio, someone with access to relevant
    BRITISH STANDARD (Oh buns)  ISO STANDARD should be able to elucidate.  (WOOOOOOO)

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What I said is not what you  think you heard.

Colin Bishop

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Re: only for ENGINEERS
« Reply #22 on: October 29, 2007, 01:41:33 PM »

Quote
You're a technological Luddite Colin

You're dead right there! Kako motors and Mighty Midgets for me every time!  O0

I think what I meant to say is that there is still a lot of stuff in use which uses Whitworth. The owner's association of my 1:1 scale boat reckon that the keel bolts have Whitworth threads. They probably hold Blackpool Tower and Hungerford Bridge together too - maybe?
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Re: only for ENGINEERS
« Reply #23 on: October 29, 2007, 04:11:54 PM »

Ok, put simply:

If a nut fits on --> it's a bolt.

bigH

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Re: only for ENGINEERS
« Reply #24 on: October 29, 2007, 05:13:08 PM »

Oh Oh - I feel a ship versus boat tide rising here   :o
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