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4 1/2 MT

Answer to a long-standing question

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Stub Mandrel13/10/2010 19:39:33
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I have seen the question 'what is a 4 1/2 MT taper here and elsewhere several times and its never been properly answered despite many attempts (including by me).
 
Last night I was  reading Machinery's Handbook in bed (sad eh?) $ 1/2 does not appear in the Morse or Stub Morse Taper sections, but instead of skipping past the Browne and Sharpe, Jarno etc. taper sections I looked at the tables properly.
 
There are three tables for American Standard Tapers - a hybrid series, with the three smallest being Browne and Sharpe. The biggest are the '3/4" per foot taper series'. In the middle and overlapping the larger series are No1 to No 7 morse.
 
With a diameter at the gage line (sic) of 1.5" is 4 1/2.
 
Key dimensions are:
Taper per foot: 0.62400"
Total length to end of tang:  4 7/8"
Length end of tang to gauge line: 4 5/8"
Gauge diameter: 1.50000"
Socket depth 4 9/16"

 So this explain why MT4 1/2 appears from time to time, but other intermediate sizes don't. It seems to have been added by our transatlantic couxcins who noticed the large step between MT4 and MT5.
 
I have always assumed the odd choices of taper for the MT series were 'retro-fitted' to the prototype tapers. The MT4 is odd in using both a regular size for the gauge line and a taper set at an exact number of thou, rather than to five decimal places - suggesting it was designed to be a particular size.
 
Intersting stuff?
 
Neil
The Merry Miller13/10/2010 20:13:01
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Stub
 
Whilst we're  on the subject of the Machinery's Handbook, how about trying to find the oldest copy that our any of our members may  still be using.
You never know but our editor may even offer a worthwhile prize to the owner of the oldest one found!!!, subject to approved validation of course and pigs taking to the air.
 
I'll kick off with my copy, Eighth Edition dated 1931. ( thats the only reason I suggested it)
I must point out that I didn't buy it new.
 
Len. P.
John Stevenson13/10/2010 21:00:44
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Better yet is a prize for anyone that can find information on that stupid R8 taper the Americans invented but forgot to put into Machinery Handbook.
 
Got a 5, 6 and 7 here,  [ got obsessed looking for that R8 <g> ]
 
John S.

Edited By John Stevenson on 13/10/2010 21:02:04

John Olsen13/10/2010 21:12:03
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Well...my Mechanical World Year Book which is an equivalent sort of publication was purchased new in 1918. (But not by me!!!!)
It does not list a 4 1/2 Morse taper.
 
MyAmerican Machinists Handbook eighth edition 1945 does have the 4.5 Morse.
 
My Machinery's Handbook is a relative latecomer, 19th edition 7th printing 1974, but for NZ$1 I can't complain...I got it secondhand from the library when it was under ten years old. It does not mention the 4.5 Morse.
 
So that tends to confirm the American theory for the half size.
 
regards
John
NEIL SMITH 113/10/2010 22:21:34
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My Tool Engineers Handbook (1949) lists 6.5 &7.5 MT,the 7.5 has the same taper as the 4.5 & 0,ie 0.624 per ft.,but the 6.5 is 0.62565 per ft..Very usefull information!
ady13/10/2010 23:52:51
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Morse tapers were so wonky morse 1 to x had no constant.
 
When they tried to standardise( 1/64 per inch or sumfink like that) they gave up and just ran with what they had, because so many machines at the time would have been adversely affected, and no-one would make any munny.
 
 
Stub Mandrel14/10/2010 08:09:52
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My guess?
 
The original Morse Taper spec was supposed ot be a taper of 5/8" in the foot, and the master tapers would have been made as close to this as possible.
 
When people elsewhere wanted to copy it without direct comparison to the masters, they had to be measured and this gave rise to the odd measurements.
 
A few decades later as extra sizes were introduced (4 1/2, 7, 7 1/2) 0.062400" per foot was chosen (or they were all prototyped at the same setting?)
 
I wonder what happened to MT6 /12?

 
Neil
Cornish Jack18/10/2010 11:50:16
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My Machinery's Handbook  is a mere youngster at edition 11 for 1942. However I have an 'upmarket'  Leather, Gilt, with Diary (1s.6d as against 1s.0d) copy of the "Practical Engineer" pocket book dated 1898!! In remarkably good nick for 112 years and full of fascinating steam related info. Nothing from Mr Morse, of course - he hadn't started tapering things then.
Rgds
Bill
TomK18/10/2010 12:54:03
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My machinery hand book 13th edition printed 1948 has a reference to a 4 1/2 taper related to the Morse. The Morse tapers listed are 1 to 7 but there is also a reference to the  Americain Standard self holding tapers numbered 0.239 to 1200.
In the list is a 4 1/2 taper.
 
 4 1/2 Amercain Standard Self Holding Tapers (A.S.S.H.T) 
Taper per foot 0.62400
Large Dia 1.5"
 
Number 4 Morse taper & A.S.S.H.T
Taper per foot 0.62326
Large Dia 1.231"
 
Number 5 Morse Taper & A.S.S.H.T.
Taper per foot 0.63151
Large Dia 1.748
 
As can be seen from above the Morse tapers for 4, 5, are are the same as the A.S.S.H.T 4,5,  So the A.S.S.H.T  4 1/2  lies about midway between the 4, 5 Morse so this is your missing 4 1/2 morse.
 
In my opinon morse just made it simple by keeping whole numbers why use a 4 1/2 when a 4 or 5 will do the same job.
 
TOM
 
 
 
Gordon W18/10/2010 14:57:52
2011 forum posts
My Machinery's Handbook, 1942, found in a dustbin, along with a , then rare, transistor radio, has no mention of half size Morse tapers. does make reference to other tapers, which seem to have been invented to suit at the time, but based on the Morse series.

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