Confused by 26, 32, 40 TPI Threads

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Confused by 26, 32, 40 TPI Threads

This topic has 23 replies, 12 voices, and was last updated 26 August 2015 at 06:09 by MEinThailand.

Viewing 24 posts - 1 through 24 (of 24 total)

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25 August 2015 at 04:31 #32554
MEinThailand
Participant
@meinthailand
Please explain what these are – what Standard/Series etc
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25 August 2015 at 04:31 #201808
MEinThailand
Participant
@meinthailand
I want to buy some boiler and pipe fittings and they are usually listed for example as 1/4 X 40, 5/16 X 32, 3/8 X 26 TPI.

What is the Standard or Series of these threads?

Having compiled a Table of these (available if you ask) together with Model Engineer Threads and Cycle threads it seems they are none of those.

Examples:-
- Model engineer threads are 55 deg
- Cycle threads are 60 deg
- Pipe fitting listed as 1/4 X 40 but ME has no 40 TPI thread
- Pipe fitting listed as 9/16 X 26 but ME has no thread for 9/16 dia.
Another question would be "what is the Form of the Model engineers thread series".

I do have the Model Engineer (ME Handbook) but it doesn't explain these questions.

By the way I have a full set of ME taps and dies but concern they might not be compatible with the listed fittings.
25 August 2015 at 05:19 #201809
Thor 🇳🇴
Participant
@thor
I am no expert but I have always assumed that the boiler fittings were ME threads (or Brass thread for 26 TPI) with a Whitworth thread angle. Someone with far more experience than me will soon enlighten us.

Tracy Tools list 1/4 x 40 ME taps and dies, for 9/16 x 26 they have Brass.

Thor

Edited By Thor on 25/08/2015 05:20:59
25 August 2015 at 05:40 #201810
MEinThailand
Participant
@meinthailand
Hi Thor and thanks for your quick reply.

The plot thickens now… what Form is a “Brass” thread?
25 August 2015 at 05:44 #201811
Thor 🇳🇴
Participant
@thor
As far as I know Brass thread uses the Whitworth thread angle.

Thor
25 August 2015 at 06:12 #201812
MEinThailand
Participant
@meinthailand
Thanks Thor, I now know what a Brass Thread is.

I should mention that I have sent the same question to the people selling the pipe fittings.

It still leaves the question unanswered:-
- Pipe fitting listed as 1/4 (plus 3/16) X 40 but ME has no 40 TPI thread (at least according to my Model Engineer Handbook)
Perhaps the Trade has generated these in 40 TPI but they aren't listed by in Tubal Cain's book.

I suppose somewhere there must be a definition of what "Model Engineer" threads are but I have never seen one.

Can anyone help, please?
25 August 2015 at 07:19 #201816
Michael Gilligan
Participant
@michaelgilligan61133
To the best of my knowledge:

The ME series is de facto, not de jure

It was, I think, "introduced" by the Model Engineer magazine [but I know not when], and uses Whitworth-form threads.

'Constant Pitch' is a convenient basis for manufacture, and therefore appropriate to miscellaneous diameters.

The use of 26, 32, or 40 tpi depends mostly on the thickness of the component being threaded … although 32 and 40 are also convenient for feedscrews.

MichaelG.

.

P.S. … If anyone can Identify the "first publication" of the ME Series, I would be grateful.
25 August 2015 at 07:25 #201818
Lambton
Participant
@lambton
For anyone who want to know all about model engineer's threads, including discussion of metric and BA alternatives I recommend them to refer to Chapter 24 of The Model Engineers Workshop Manual by George Thomas.
25 August 2015 at 07:26 #201819
Michael Gilligan
Participant
@michaelgilligan61133
Colin Usher has a useful page

MichaelG.
25 August 2015 at 07:36 #201820
JasonB
Moderator
@jasonb
This is quite a good site and shows the form of ME, Cycle, CEI and brass along with a lot of others
25 August 2015 at 08:02 #201822
MEinThailand
Participant
@meinthailand
Posted by Lambton on 25/08/2015 07:25:57:

For anyone who want to know all about model engineer's threads, including discussion of metric and BA alternatives I recommend them to refer to Chapter 24 of The Model Engineers Workshop Manual by George Thomas.

Ah! A most useful reply, thank you.

I have the George Thomas book open in front of me now. On page 266 there is a Table II listing the 'ME' series (amongst other sizes).

1/4 (plus 3/16) X 40 are listed as being ME threads.

The origin of the ME series is given as "… established by a committee of the SM & EE in 1912…)…

There are no details of (for example) core diameters but I suppose these could be worked out using the Whitworth Form dimensions. (It – the book – doesn't actually say that the ME series is Whitworth Form)
25 August 2015 at 08:15 #201823
Michael Gilligan
Participant
@michaelgilligan61133
**LINK**
25 August 2015 at 08:41 #201825
Michael Gilligan
Participant
@michaelgilligan61133
Posted by MEinThailand on 25/08/2015 08:02:24:

There are no details of (for example) core diameters but I suppose these could be worked out using the Whitworth Form dimensions.

.

Hint: That nice Mr. Usher has done the hard work … check the links on his page.
25 August 2015 at 08:51 #201827
MEinThailand
Participant
@meinthailand
Posted by Michael Gilligan on 25/08/2015 08:15:57:

**LINK**

This is very useful indeed. It points to the inside of a hardcopy book "Guide to World Screw Threads" By P A Sidders.

This gives the origins of the ME series and two tables of sizes and thread pitches. One Table also gives data such as Major and Minor diameter and Tapping Drill sizes, but not for the 60 TPI threads.

Strangely, again, it does not state that the series is based on the Whitworth Form nor does it give the thread angle.

Many thanks Michael, I'll try to get a copy of that book.
25 August 2015 at 08:52 #201828
Black Cat2
Participant
@blackcat256889
The Tap and Die company,London have an online list of threads per inch and tapping drill sizes on one page .might help.
25 August 2015 at 08:55 #201829
Neil Wyatt
Moderator
@neilwyatt
Sometimes the ME threads that fit into the other common series are not listed, presumably to help folk avoid buying two of the same tap and die.

Neil
25 August 2015 at 09:14 #201834
Michael Gilligan
Participant
@michaelgilligan61133
Posted by MEinThailand on 25/08/2015 08:51:17:

Strangely, again, it does not state that the series is based on the Whitworth Form nor does it give the thread angle.

.

In 1912 … before the World went mad … Whitworth was the form for vee screw threads.

MichaelG.
25 August 2015 at 09:38 #201841
MEinThailand
Participant
@meinthailand
Posted by MEinThailand on 25/08/2015 08:51:17:

Posted by Michael Gilligan on 25/08/2015 08:15:57:

**LINK**

This is very useful indeed. It points to the inside of a hardcopy book "Guide to World Screw Threads" By P A Sidders.

This gives the origins of the ME series and two tables of sizes and thread pitches. One Table also gives data such as Major and Minor diameter and Tapping Drill sizes, but not for the 60 TPI threads.

Strangely, again, it does not state that the series is based on the Whitworth Form nor does it give the thread angle.

Many thanks Michael, I'll try to get a copy of that book.

Interestingly, Table II in the George Thomas books (where he *s the ME series threads) differs from that in the "Guide to World Screw Threads".

I don't have time immediately to itemise the differences but will do it later today or tomorrow.

Please bear in mind that I'm not trying to research ME threads (or threads in a broader sense) I'm just trying to make sure that when I buy pipe fittings that I know what thread it is and to avoid buying another set of taps and dies. Pretty important when the threads will be used on a 1/2 sized traction engine with a boiler running at 125 psi.
25 August 2015 at 09:43 #201842
Harold Hall 1
Participant
@haroldhall1
If I may be allowed to give a plug for my book "Metalworkers Data Book" it gives thread forms, pitches, core diameters, tapping drill sizes, % depth of thread using the quoted drill sizes, dimensions given in both metric and Imperial, etc. and for the following thread types

Metric course
Metric fine
Metric Spark plugs
Metric conduit
BA
UNC
UNF
BSW
BSF
ME
British standard brass
British standard cycle
British standard pipe parallel
British standard pipe taper
National pipe taper
Metric threads recommended for model engineering
The book gives outline drawings for their thread forms .

The book also has details for many other subjects,see link above for details

Myhobbystore have it listed here

Harold
25 August 2015 at 09:47 #201843
Nigel McBurney 1
Participant
@nigelmcburney1
According to Machinerys Screw thread book,1965 edition the model engineers thread was established in 1912 by a meeting of the SMEE and the editor of the Model Engineer,it lists a series of fine Whit form threads from 1/8 to 1/2 inch with a variation of pitch 40 ,32 and 26 .. then mentions that combinations of threads from 1/8 to 9/16 with pitches varying i.e. 60 ,40 and 32. Instrument makers also used lots of specials to suit brass tubes and eyepiece fitting,and were sometimes available off the shelf or to special order,taps were more commonly used,male threads tended to be chased with whit form chasers,though special 40 tpi dies were used on capstan lathes for higher volumes, i.e. 1000 batches (carbon cut thread dies would last for thousands of pieces) Brass thread apparently did not have any recognised standards, it seemed to stem from the millions of gas lamp fittings in Victorian times,they are 26 tpi and whit form. So take it that all the model engineer threads ,brass thread and bsp pipe are to whit form.When I was apprenticed (1958) as an instrument maker all the threads apart from BA were whit form,plus the occasional Acme and Square thread, and so was a lot of other engineering. Outside of work ,cycle threads (60 degree form)were encountered on push bikes and some motor cycles,all nuts were whit size,then came cars with unified threads and a/f nuts,then came further confusion with metric, I can never understand why cycle threads were 60 degree form used from early time instead of whit form. I can understand why there is now confusion ,as when I was trained you just knew that the common fine threads were Whit form.
25 August 2015 at 09:48 #201844
Swarf, Mostly!
Participant
@swarfmostly
Posted by Michael Gilligan on 25/08/2015 09:14:55:

Posted by MEinThailand on 25/08/2015 08:51:17:

Strangely, again, it does not state that the series is based on the Whitworth Form nor does it give the thread angle.

.

In 1912 … before the World went mad … Whitworth was the form for vee screw threads.

MichaelG.

My first lathe was a quite old Carl Hurth, it was made in Germany but all the threads were Whitworth.

Best regards,

Swarf, Mostly!
25 August 2015 at 13:49 #201872
Ian S C
Participant
@iansc
Swarf, when I first got my lathe, one job was helping to restore a 1932 Lanz Bulldog tractor, all the threads on it were either BSW, or BSF. Later Lanz tractors went metric.

The model engineer thread was originally known as the Whitworth extra fine thread (55*). For those in the USA, a useful fine thread is UNEF (60*).

Ian S C
25 August 2015 at 14:57 #201887
Bob Youldon
Participant
@bobyouldon45599
Good afternoon,

To be honest, should I be building a half sized traction engine I'd use fittings more suited to the scale, fittings with the BSP taper thread form or from the NPTF range, although I'd advise anyone here in the UK to consult with their boiler insurance provider prior to any decision is made on any particular thread form or fittings, who may have a view on the matter.

Regards,

Bob
26 August 2015 at 06:09 #201987
MEinThailand
Participant
@meinthailand
Well, thank you everyone who has helped me to understand the ME Series of threads.

I needed to have this knowledge because I want to buy some steam engine pipe fittings and I wasn't sure what the threads stated in the vendor's catalogue were nor if I had the right taps and dies to make matching components.

With your help I have compiled the Table below which shows three main pieces of information:-

1) The Threads forming the ME Series as reported in a book "Guide to World Screw Threads" by ISBN 0-89381-1092-9.

The above Series is repeated in the book "The Model Engineers Workshop Manual". ISBN 1-85761-000-8 by Geo. H. Thomas. Seems he was correct and my comment in a previous post is withdrawn with apologies.

2) Additional threads reported in the same "Guide to World Screw Threads" book as being "in regular use".

3) The taps and dies that were included in a commercial ME Series tap and Die set that I purchased from one of our regular suppliers. (Plus a few I bought separately)

This may be important to you if you are thinking to buy a set because you, like me, will probably end up need supplementary taps and dies.

The fittings I was interested in purchasing include some for which I do not have taps and dies, namely 1/2" X 32 and 9/16" X 26 both of which are not in the ME Series.

A Standard for the ME Series

It seems that there is no published Standard for ME Series threads. The range has grown by demand from users and the trade has stepped in to supply the demand.

The situation as above is supported by Geo Thomas in his book on page 266. (I would like to quote but the book is copyright).

Whitworth Form

Although no publication I have seen states that the ME Series is Whitworth form, the description of the ME Series on page 19 of "Guide to World Screw Threads" appears in Section A "BRITISH THREADS OF WHITWORTH FORM". So that seems to confirm that Whitworth is the correct thread form.

Below is the Table I have compiled illustrating the ME Series of threads.

Once again thank you everyone who has contributed, it seems that my question has been answered.
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