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The New Zealand Railways Magazine, Volume 5, Issue 6 (October 1, 1930)

The History of the Milling Gutter

page 61

The History of the Milling Gutter

The ancestry of the milling cutter as we know it to-day can be traced back to the rotary file. This file was invented by a French clock-maker during the eighteenth century. He called it a “fraise,” because of its strawberry-like surface, and, up to this day, the French still call a milling cutter a “fraise” (meaning strawberry). This artistic name compares favourably with the Englishman's first end mill, which he called “rose - bit,” the teeth of which resembled in shape a rose.

For nearly a century the milling cutter made but little headway—except for the fact that the teeth were wider spaced and cut more regularly. Nevertheless it was a great advance upon the old rotary file. The sharpening of the early cutters had to be done with a file, a process that involved softening and rehardening. At the best this was a tedious and costly procedure and far from satisfactory. With the advent of the machine cutter grinder, the milling cutter commenced to move more rapidly, and was then readily taken up by the clock makers, sewing machine, push bike, and rifle manufacturers.

As Used in the N.Z. Railway Workshops. A modern milling machine made by J. Parkinson and Son, Shipley, England.

As Used in the N.Z. Railway Workshops.
A modern milling machine made by J. Parkinson and Son, Shipley, England.

With the introduction of high speed steel another change of design followed in the milling cutter. It was found that, although the teeth had been more widely spaced, the spacing was insufficient. With the faster speeds and heavier cuts made possible by using high speed steel, the teeth of the cutter became clogged with chips and thus the cutters were frequently fractured or broken. Coarser teeth with more backing were then tried. On fine cuts, however (owing to the first cutting tooth going out of action before the next tooth came into operation), these coarser teeth “hammered.” This was overcome by increasing the spiral of the cylindrical cutter from 10 deg. to 25 deg. thereby bringing the second tooth on to the work before the first tooth got clear of its cut.

The early motor-its possibly remember the noise caused by the hammering of their crown gears. This was due to a similar mechanical fault as occasioned by the hammering of the milling cutter. It was silenced by the introduction of spiral cut teeth, which are not only stronger, but quiet and more co-operative than the single acting snub tooth.

During the Great War the milling cutter came up for serious consideration by the production engineer.

The call of the Allies for more and still more munitions had to be answered, and a committee of Machine Tool Experts during 1915–16 experimented with various tools including the cylindrical, side and form milling cutters. After making various experiments and lengthy tests, it was found that the spiral of the cutter referred to could be advantageously increased, and was increased from 25 deg. to 35deg. A test of an 8in./41/2in. cylindrical cutter on a 2in. arbor gave the following results: .9 cubic inches of 35 ton tensile steel were removed per one h.p. per page 62 minute. On a continuous run of one hour with the same cutter .78 cubic feet of 35 ton steel were removed with a varying h.p. of 24 to 27. Other successful tests were carried out on 50 ton tensile steel which was being used extensively. The results of the tests referred to compare very favourably with our experience in the New Zealand Railway Workshops.

With the object of determining the most satisfactory and economical means of removing the most metal per minute per horse power another noteworthy test was carried out on 35 ton tensile steel. It will be noted, by the following table, that the result of the test clearly demonstrates that the milling cutter is slightly more efficient on light than on heavy cuts, subject to the operator correctly balancing the feeds.

Table A.
Depth of Cut Feed measured in Cubic inches
in inches. inches per min. per H.P. min.
.187 21.50 .87
.385 9.50 .86
.500 6.25 .82
.625 4.00 .83
.750 4.00 .79
1.000 2.75 .80
Table B.
Depth of Cut Feed measured in Cubic inches
in inches. inches per min. per H.P. min.
.187 21.25 .75
.375 9.10 .74
.500 5.75 .67
.625 3.75 .70
.750 3.75 .61
1.000 2.50 .54

In tables A and B it will be seen with a cut .625ins. deep and a feed of 4ins. per minute, that more metal was removed than with a .750ins. depth cut and the same feed. This clearly shews that, to get the most out of a milling cutter, the milling specialist requires a thorough knowledge alike of the machine and cutting tools and materials with which he works. To acquire this knowledge takes time, and concentration, But it is time and concentration that makes the specialist who, in modern machine shop practice, is the most valuable labour asset in the field of modern production.

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