"At a speed of, say, two hundred feet per minute, the chip comes writhing and twisting, almost red hot, in a continuous length, shooting here and there, everywhere but the chip box; and quick must be the workman that manages to keep well out of the way of it, for it 'sticketh like a brother' when once he gets tangled in it.

"Possibly, in time, a way will be found to take care of such chips. Until this is done, however, a moderate speed is most desirable. We find that on steel, where there is no considerable thickness of metal to remove, a speed of one hundred feet a minute is very satisfactory. This allows taking care of chips, and the tools stand up well under it. In turning gray iron, where the scale is to be removed, about seventy feet per minute is giving us the best results. Naturally, however, there being so many different kinds of materials to work up, and each one of these varying more or less themselves, there can be no set rule for speed. Each job will work out a rate for itself. The main thing is to get out the job as fast and as well as possible, and at the same time to lose as little time as may be in grinding the tool.

"Another word about the saving to be effected. This will depend among other things upon the number of machines that are run. If only one machine runs on a job, there will not be a saving of two thirds simply because the speed is trebled. It must be remembered that perhaps 50 per cent of the time for doing a job on a single machine is used in jigging the piece and setting the tool.

"The high initial cost of the new steels has made it necessary to devise means for reducing the quantity of metal in the tools used. The result has been the production of some very ingenious schemes for holding cutters. The lathe tool holder is, of course, familiar to all. Milling cutters, hollow mills, and reamers with inserted teeth, are scarcely less familiar. It is now true that we are making all these tools with inserted cutters of rapid cutting steel at less cost than the old carbon steel tools. At the same time they are doing from three to ten times the work, and at a much greater speed."

The question of speeds and feeds is an important one in connection with that of lathe tools, whether the old carbon steel is used or the new high-speed steel known as self-hardening is that selected.

As has been said in the observation on the form and qualities of tools, a great deal depends, not only on the kind of metal worked, but also on the quality of the particular kind that is to be machined.

With the old form of tools made from the old carbon steels, cast iron was turned at a speed of from 20 to 25 feet per minute; soft steel, 25 to 30 feet; wrought iron, 35 to 45 feet; and ordinary brass at from 50 to 100 feet.

With the present tools and methods such speeds are considered child's play, and the speeds at which different materials are turned, assuming a medium grade of metal, will more likely be given as

Soft Cast Iron...................................

50

to

60

feet.

Hard Cast Iron..............................

20

to

40

,,

Hard Cast Steel..............................

30

to

40

,,

Soft Machine Steel...........................

30

to

40

,,

Hard Machine Steel..........................

20

to

30

,,

Wrought Iron................................

35

to

45

,,

Tool Steel, Annealed.........................

20

to

30

,,

Tool Steel, not Annealed.......................

15

to

20

,,

Soft Brass......................

110

to

130

,,

Hard Brass..................................

90

to

110

,,

Bronze....................

60

to

80

,,

Bronze, Gun Metal...................................

40

to

60

,,

Grey or Red Fiber...........................

40

to

60

,,

The feeds will not vary in the same proportion as the speeds, or in fact bear any fixed relation to them.

A prominent writer on this subject says that: "An important point is, that other conditions being equal, the increase of speed involves a diminution of feed. Hence it is not possible to reduce the question of speeds and feeds to formulae, or tables."

This is hardly correct as to the fact of the inverse relation of speeds and feeds under varying circumstances, as the same author admits further on by saying: "Each class or job must be settled by itself in the practice of any given shop." He might have said, with each different material, and as to whether it is a roughing, sizing, or finishing cut.

Some practical observations in point may not be amiss, as they are taken from actual practice and may be held as good mechanical data, with the use of high-speed steel.

Roughing cuts in soft cast iron may be made with a feed as coarse as 4 to 5 per inch, with a tool whose leading corner is slightly rounded.

Roughing cuts on soft machine steel forgings, 5 to 8 per inch.

Sizing cuts on soft cast iron, 12 to 16 per inch.

Sizing cuts on soft machine steel, 16 to 20 per inch.

Finishing cuts on soft cast iron, with a narrow-point tool, may be from 15 to 25 per inch.

Finishing cuts on soft machine steel, with a narrow-point tool, 20 to 40 per inch.

Finishing cuts on soft cast iron, with a wide point, practically straight-faced tool with corners slightly rounded, the feed may be, for soft cast iron, from 1 to 4 per inch.

Under like circumstances, for soft machine steel, the cut may be from 4 to 8 per inch.

In these different cuts the speeds may be substantially as stated in the table given above, except the last, in which case the speed must be very much slower, less than half the speeds there given.

Further than these figures it will be found difficult to set down a range of speeds and feeds that will be of any practical value. It must be left for the superintendents, foremen, and mechanical engineers in charge of work to determine these facts and to adopt such standards as may be found by actual experiment is most satisfactory under the circumstances and conditions governing the work, and which will, of course, include a careful study of the materials that are to be machined.

The lubrication of tools has a very considerable influence upon the performance of lathe tools, and when used should materially increase the output of the machines by permitting faster speeds, heavier cuts, and greater feeds. Lubrication prevents the friction that otherwise attends heavy cutting, and therefore prevents heating to both the work and the tool. A steady stream flowing upon the cutting-tool will tend to carry away such heat as will, to a certain extent, always take place. Naturally a well lubricated tool will last longer in proper condition for cutting than one that is not lubricated, as the friction of the metal across the edge of the tool will be much less.