PDA

View Full Version : HSM May/June Article: The Odd Screw



Paul Alciatore
04-25-2009, 03:49 AM
I was reading this article by Paul Holm and started wondering about non-standard screw sizes and how common they might be. The problem that formed the basis of the article was a Craftsman tool holder that used a 3/8"-18 screw to secure the tool. Why would they do that.

I have a few tool holders that haven't been used for some years now since I made my quick change holder so I broke them out and checked them out. All are for 1/4" tool bits. Here's what I found:

Armstrong, U.S.A., No 0-R: 3/8"-18 screw

Armstrong, U.S.A., No 0-S: 3/8"-18 screw

J. H. Williams, U.S.A., No 0-L: 3/8"-18 screw

No name, import, no number: 5/16"-18 screw

All the US made holders have the 3/8"-18 screw and the import has a 5/16"-18 TPI screw. Someone likes 18 TPI. Apparently the "Odd Screw" is not that odd after all. Craftsman isn't the only one who used it. And yes, I know Craftsman is just another manufacturer with their name on it. They probably just said to make them the same as the manufacturer's own line.

Armstrong seems to still be in the business as I saw their holders listed in at least one catalog. I can only wonder if they still use the same screw and if they could supply replacements. Their holders are $100+ so expecting them to supply replacement parts would not be out of the question. But at what price? Perhaps the author has it right, make your own.

JCHannum
04-25-2009, 07:19 AM
In the case of the toolholders, it is probably a legacy issue. Toolholders date back to the beginning of time when there were no real standards, and 18TPI was probably not uncommon. Another thread that appears frequently is 12TPI, 1/2"-12 being frequently used on older machinery.

It was not until WWII that standards were created in the interests of interchangeability. This left some manufacturers of specialized equipment with the quandary of what to do with their product, continue the now non-standard thread and make replacements for all existing parts difficult or continue with the odd thread. Apparently Armstrong etal decided on the latter and 18TPI is the standard thread for rocker toolholders.

websterz
04-25-2009, 08:26 AM
5/16-18 isn't an odd thread...I use it almost every day.

John Stevenson
04-25-2009, 08:27 AM
In the case of the toolholders, it is probably a legacy issue. Toolholders date back to the beginning of time when there were no real standards, and 18TPI was probably not uncommon. Another thread that appears frequently is 12TPI, 1/2"-12 being frequently used on older machinery.



1/2" x 12 was the first real standard, it British Standard Whitworth and was in use before any other standards were dreamed up.
It's NEVER been withdrawn and is still current today and used all over the world.
The Taiwanese use it and later the Chinese and Indians copied it that's why you come across this on mill drills etc and call it a bastard thread when in fact only the Americans made their 1/2" standard 13 instead of the existing 12.

Why ?? no one knows but as is common it was to tie in to certain manufactures and say "We invented this "

Rather ironic that in 1841 when Whitworth come up with his standards of 55 degrees and rounded tops he had enough knowledge to know it was the best thread design.
Twenty odd years later in the 1860's when Sellers can up with what is now the Unified series he did it for ease of use with 60 degree angle and flat crests.

Modern tests on both thread forms have determined that the Whitworth thread is stronger. I feel that Whitworth is one of the most under rated engineers we had.
It's well worth reading the book Sir Joseph Whitworth to see how badly treated he was.

http://www.amazon.co.uk/Sir-Joseph-Whitworth-Norman-Atkinson/dp/0750912111

.

bob ward
04-25-2009, 09:09 AM
1/2" x 12 was the first real standard, it British Standard Whitworth and was in use before any other standards were dreamed up.
It's NEVER been withdrawn and is still current today and used all over the world.
The Taiwanese use it and later the Chinese and Indians copied it that's why you come across this on mill drills etc and call it a bastard thread when in fact only the Americans made their 1/2" standard 13 instead of the existing 12.


60 UNC and 55 Whitworth nuts and bolts are often used one with the other, except for 1/2" of course, in countries where they occur together.

Out of curiosity, are the Taiwanese et al threads usually 55 Whitworth form or 60 form?

jkilroy
04-25-2009, 09:19 AM
Isn't 12tpi the standard fine thread for most everything 1" diameter and above? I have a 1x12 as well as a 2 1/4 x 12. I know 9/16x12 is common as well.

Teenage_Machinist
04-25-2009, 04:59 PM
1/2-12? That is much better than 12/13!

tony ennis
04-25-2009, 06:58 PM
" Sir Joseph Whitworth (Hardcover)
by Norman Atkinson (Author) "

Har! Go Norm!

John Stevenson
04-25-2009, 07:12 PM
No it's not by Norman because you can understand what's written.

.

dockrat
04-25-2009, 07:19 PM
No it's not by Norman because you can understand what's written.

.

LOL!!!! Thats your second best line in 2 days John!!! :D

.RC.
04-25-2009, 07:20 PM
I think the entire metric series is an odd bod thread..Every bloody country uses a different bolt head size and thread pitch/bolt diameter..

Whitworth FTW..

thistle
04-25-2009, 09:22 PM
odd thread of the week - 3/8 x 19 BSP,
aaarrrgggghhhhh 19 tpi???????

lucky i had the right tap and die.

.RC.
04-25-2009, 09:58 PM
odd thread of the week - 3/8 x 19 BSP,
aaarrrgggghhhhh 19 tpi???????

lucky i had the right tap and die.


What is odd about 3/8 X 19 BSP it is a standard thread better then 2"X11 1/2 NPT.. :D

Jeffw5555
04-25-2009, 10:25 PM
The only fault I see with the whole Whitworth thread thing is the way the hex head sizes were set. (needing goofy-a$$ed wrench (spanner) sizes)

It's the reason I sold my 1959 Land Rover. That bastard-vehicle had multiple kinds of fasteners all over it.

BTW, what Old Blighty joker thought that King Dick was a good name for tools?

SDL
04-26-2009, 02:53 AM
The only fault I see with the whole Whitworth thread thing is the way the hex head sizes were set. (needing goofy-a$$ed wrench (spanner) sizes)

It's the reason I sold my 1959 Land Rover. That bastard-vehicle had multiple kinds of fasteners all over it.

BTW, what Old Blighty joker thought that King Dick was a good name for tools?

Wrong, as Whitworth was the first standard thread all head combinations after that are the goofy ones:D:D

oldtiffie
04-26-2009, 03:53 AM
Given that US and UK threads are specified in inches and that inches are specified in mm - as are metric threads - then it follows that all threads of all systems are ultimately specified in mm - and are therefore metric.


International inch
In 1958 the United States and countries of the British Commonwealth defined the length of the international yard to be 0.9144 meter.[citation needed] Consequently, the international inch is defined to be equal to 25.4 millimeters.

The international standard symbol for inch is in (see ISO 31-1, Annex A). In some cases, the inch is denoted by a double prime, which is often approximated by double quotes, and the foot by a prime, which is often approximated by an apostrophe. The two parts are sometimes separated by a dash[citation needed] (for example, 6 feet 2 inches is denoted by 6′-2″). In most languages the word "Thumb" means an Inch.

from:
http://en.wikipedia.org/wiki/Inch

It is similarly so for volume (litre), mass (kilo-gram) etc. etc.

Don't believe or don't like it?

Tough.

That's how the Governments in US and UK legislated it!!

http://en.wikipedia.org/wiki/US_measurements

http://en.wikipedia.org/wiki/Metrication

Or - sorry about the pun - not - metrication rules!!

Jeffw5555
04-26-2009, 08:40 AM
Wrong, as Whitworth was the first standard thread all head combinations after that are the goofy ones:D:D

I knew that it was the first; and it could be argued the best from a thread strength standpoint, but why didn't they use logic for the hex stock? (i.e. the spanners/hex stock/across flats three sizes above the thread size, e.g. a 3/8" UNC bolt takes a 9/16 wrench....)

That's what I mean by goofy.....:D :D

hardtail
04-26-2009, 08:47 AM
Harley runs different thread counts, not coarse or fine, the aftermarket engines seem to try and get back to normal though.......I always thought it was their way of getting you to stop by and lighten your wallet some more.......

loose nut
04-26-2009, 09:30 AM
Rather ironic that in 1841 when Whitworth come up with his standards of 55 degrees and rounded tops he had enough knowledge to know it was the best thread design.

.

If you read up on Whitworth you will see that he didn't decide directly on the 55 Deg. thread form because he thought it was the best. He went to all the major shops of the day and measured the thread forms that they used and then he averaged it out to become the Whitworth series, he just figured that great minds will think alike and so an average of these would work best.
That was his great leap of brilliance not the actual design of the threads. It seems like a simple thing know but he was the first to do it. If the other builders had different thread forms his series of threads could have been 58 or 62 Deg. or what ever.

John Stevenson
04-26-2009, 09:52 AM
If you read up on Whitworth you will see that he didn't decide directly on the 55 Deg. thread form because he thought it was the best. He went to all the major shops of the day and measured the thread forms that they used and then he averaged it out to become the Whitworth series, he just figured that great minds will think alike and so an average of these would work best.
That was his great leap of brilliance not the actual design of the threads. It seems like a simple thing know but he was the first to do it. If the other builders had different thread forms his series of threads could have been 58 or 62 Deg. or what ever.

Yes you are correct and what I meant to say [ I often type faster than my brain and that's not hard :D ] was that with the little knowledge about at the time it was ironic that the angle chosen [ by whatever means ] turned out to be the best as proven many years later in tests.

To get a better feeling of Deja Vu read up on the Whitworth rifle and field gun with the design knowledge we have today.
Like many great men his inventions have come back as new inventions by others, as I say he was very underrated for his day.

British history is full of these giants often decried off hand for political gain by others of a lesser nature, Sir Frank Whittle falls into this class as well.

Paul Alciatore
04-26-2009, 03:02 PM
odd thread of the week - 3/8 x 19 BSP,
aaarrrgggghhhhh 19 tpi???????

lucky i had the right tap and die.

Where do you get off calling it "odd" if you had BOTH the tap and the die? Can't be that odd in your shop.