Cutting Data

SELECTING SPEEDS and FEEDS (Turning and Parting Off)

The following table shows suggested r.p.m. for the most commonly machined materials. Look for the nearest diameter to the one you wish to cut, and move across to the workpiece material. Then simply read off the r.p.m.
You should then select the nearest speed available on your machine, taking safety and other practical considerations into account. You can happily run slower if necessary, especially if it is unsafe to rotate the workpiece or chuck at the indicated speeds.

NOTE: Vibrations due to worn bearings or machine imperfections (i.e. damaged vee belts etc) may mean that the suggested r.p.m. cannot be achieved. Tests carried out by ourselves and a local model engineer discovered that in some cases it was desirable to reduce r.p.m on finishing cuts, due to machine imperfections.

 Cutting Dia  Mild Steel  Stainless  Brass/Bronze  Cast Iron  Aluminium
 mm  inch  R.P.M  R.P.M  R.P.M  R.P.M  R.P.M
 3  1/8  *  *  *  *  *
 6  1/4  *  2400  *  *  *
 10  3/8  2200  1430  *  *  *
 13  1/2  1700  1100  *  2200  *
 20  3/4  1100  700  2500  1400  *
 25  1  890  570  2000  1150  *
 32  1.1/4  700  450  1600  900  2000
 38  1.1/2  580  380  1300  750  1700
 50  2  450  290  1000  570  1300
 63  2.1/2  350  230  800  450  1000
 75  3  300  190  680  380  850
 100  4  220  140  500  280  640
 125  5  180  110  400  230  510
 160  6  140  90  320  180  400

* We assume your machine will not run at speeds faster than 2500rpm. Where the theoretical speed is greater than that, we have indicated with an asterisk.

FEEDS should be set at the maximum possible per revolution, bearing in mind:-

a) The required surface finish.
b) The power of the spindle motor.
c) The rigidity of the machine, workpiece and set-up.
d) The strength of the insert corner radius.
e) Indexable inserts generally like to be worked at minimum 0.1mm (0.004 ins) /rev wherever possible.

NOTE: Where a large amount of stock is to be removed, the cutting edge will generally last longer if shallower cuts are taken at higher feeds - as opposed to deeper cuts at lighter feeds.

SELECTING SPEEDS and FEEDS (Milling)

The following table shows suggested r.p.m. for the most commonly machined materials with carbide grade H13A. Look for the diameter of your milling cutter, and move across to the workpiece material. Then read off the r.p.m. as appropriate for a roughing or a finishing cut. You should then select the nearest speed available on your machine, taking safety and other practical considerations into account. You can happily run slower if necessary, especially if it is unsafe to rotate the chuck at the indicated speeds.

Cutter Dia  Mild Steel  Stainless  Brass/Bronze  Cast Iron  Aluminium
 mm  R.P.M  R.P.M  R.P.M  R.P.M  R.P.M
 12  1600  1050  1900  1900  *
 16  1200  800  1400  1400  *
 20  950  650  1100  1100  3000
 25  760  500  900  900  2500
 50  380  250  450  450  1300
63  300  200  350  350  1000

* We assume your machine will not run at speeds faster than 3000 rpm. Where the theoretical speed is greater than that, we have indicated with an asterisk.

FEEDS should be calculated by the following simple formula, where feed per insert should be kept between 0.05 and 0.10 mm:-

Feedrate (mm/min) = R.P.M. x Number of Inserts in Cutter x Feed per Insert

The feed per insert should be based on:
a) The required surface finish.
b) The power of the spindle motor.
c) The rigidity of the machine, workpiece and set-up.

NOTE: Where a large amount of stock is to be removed, the cutting edge will generally last longer if shallower cuts are taken at higher feeds - as opposed to deeper cuts at lighter feeds.

POWER REQUIREMENTS:

Some people get worried about power requirements when we talk about facemilling on light, low-powered machines. Very often, their worries are unfounded. The following example should give an idea as to the practicalities:- Using a 63mm dia CoroMill® 245 cutter to cut mild steel with H13A grade inserts:-

At 350 rpm, with a table feed of 5 ins/minute, and assuming a cut of 1½ ins wide x 1/16 ins deep. The motor power required to drive the cutter would only be 0.38 Horsepower (=0.28kW)! Doubling the feed would double the power required, as would doubling the depth of cut. These cutters are so 'kind' to the machine, one of our customers commented that using it was 'just like mowing the grass!'

In general terms, it can be said that 1 horsepower can remove 1 cubic inch of steel in 1 minute. (or 1.5 cu in of cast iron)

Therefore, by multiplying the feed/minute (in inches) by the width of cut (in inches) by the depth of cut (in inches), an approximation can be made as to the required spindle motor power. For example, a feed of 4 ins/minute, with a width of cut of 1/2 ins, and a depth of cut of 1/8 ins would use approximately 4 x 1/2 x 1/8 = 1/4 horsepower.