On July 11, 1938 The National Machine Tool Builders Association Commettee on Milling Machine Nose Standardization approved as Standard the dimensions and configuration of milling machine spindles and arbors that we know as the No. 30, No. 40 and the No. 50 milling machine tapers.
The construction was covered by U.S. Patent No. 1794361.
There were six sizes proposed, No.'s 10 through 60 The No 10 MMT had a gauge diameter (big end) of 5/8 inch. The No. 20 was 7/8 inch.
These sizes were not produced.
The gauge diameters of the others are as follows:
No. 30 1 1/4 in.
No. 40 1 3/4 in
No. 50 2 3/4 in.
No. 60 4 1/4 in.
All Tapers are of 3.500 in. per foot.
Most of the dimensions are rather loosely toleranced. All are in Inch Measure.
All Standard Spindle noses must project out from the column or head by a minimum amount and the outside diameter of the spindle nose is held to close tolerances.
No. 30 O.D. - 2.7493-2.7488
No. 40 O.D. - 3.4993-3.4988
No. 50 O.D. - 5.0618-5.0613
No. 60 O.D. - 8.7180-8.7185
There are two spindle keys and they are specified as a tight fit in the spindle key slot.
The key widths are:
No 30 and No 40 - .6255-.6252
No 50 - 1.0006-1.0002
No 60 - 1.000-0.999
There are 4 threaded holes equally spaced but at 45 degrees to the keys.
No. 30 - 3/8-16 NC-2
No. 40 - 1/2-13 NC-2
No. 50 - 5/8-11 NC-2
No. 60 - 3/4-10 NC=2
Nose Projection from Column or head (minimum)
No. 30 1/2 in.
No. 40 5/8 in.
No. 50 3/4 in.
No. 60 1 1/2 in.
The care taken with the configuration of the spindle nose is to allow large cutters (face mills) to be mounted directly on the front of the spindle without locating on the internal tapered surface.
There are no tight tolerances on any dimension of the tapered part of the arbors or tool holders except for the 3.500 in. per foot taper. They must locate on the taper only.
Drawbar threads are as follows:
No. 30 1/2-13 NC-3
No. 40 5/8-11 NC-3
No. 50 1inch 8 NC-3
No. 60 1 1/4-7 NC-3
No, that is not a mis-print the drawbar threads are specified as a No. 3 (precision) fit.
Dimensions Taken from The American Machinist's Handbook, Colvin and Stanley, Seventh Edition, 1940.
very interesting. Thank you.
I was asked last week what the R and the "8" mean in a R8 collet. I have asked several people so far, but not gotten any answers.
Any help or direction where i could get help ??
Thank you !
I make the Arbors and Spindles in ISO tapers 30, 40 & 50 for Milling Machine Builders in India.
we however work with metric, but originally they are all Inch dimensions.
Jim if you could Scan a Copy of this info from the original book (1940), it would make a very good picture to hang on a wall of our shopfloor.
We make Spindles and milling arbors with these Tapers, for the Indian Machine Tool Builders.
Thank you and best regards
JimK hasn't posted to this site since 2006 (check his posts).
However, at this moment, ebay has that exact book for sale, as a Buy It Now, for $29.95.
American Machinists' Handbook + Shop Terms ~ 1940 | eBay
If you desire that exact verbiage.
The American Machinists Handbook was a competitor to Machinery's Handbook, which should have the same information.
Old machinist handbooks are on ebay quite frequently. I suspect that a patient person could collect each year's book, spanning back several decades, if they so desired.
IIRC, Jim Kizale passed several years ago.