Practical Treatise on Milling and Milling Machines/Chapter 9
CHAPTER IX
Milling Operations — Cam Cutting, Graduating and Miscellaneous Operations
Cam Cutting. Face, peripheral and cylindrical cams of all ordinary sizes can be cut upon a milling machine, and a far more satisfactory job can be obtained than is possible by drilling around the outline on a cam blank, breaking it off and then milling or riling to a line.
When it is required to cut several cams of the same outline at frequent intervals, it is an advantage to add the cam cutting attachment, illustrated and described in Chapter V, to the equipment of the machine. The formers that are required to produce the different cams can be preserved, and it is then only a matter of a few minutes' time to set up the machine to cut any number of cams for which a former is at hand.
Another method that is often followed, in cutting peripheral cams, especially those for use on automatic screw machines, is that of using the spiral head and a vertical spindle milling attachment. Illustrations of this are shown on pages 187 and 188. The spiral head is geared to the table feed screw, the same as in cutting ordinary spirals, and the cam blank is fastened to the end of the index spindle. An end mill is used in the vertical spindle milling attachment, which is set in each case to mill the periphery of the cam at right angles to its sides, or, in other words, the axes of the spiral head spindle and attachment spindle must always be parallel to mill cams according to this method. The cutting is done by the teeth on the periphery of the end mill. The principle of this method is as follows: Suppose the spiral head is elevated to 90°, or at exact right angles to the surface of the table (see Fig. 69), and is geared for any given lead. It is then apparent that, as the table advances and the blank is turned, the distance between the axes of the index spindle and attachment spindle becomes less. In other words, the cut becomes deeper and the radius of the cam is shortened, producing a spiral lobe, the lead of which is the same as that for which the machine is geared. 
Fig. 69
Fig. 71
Now, suppose the same gearing is retained and the spiral head is set at zero, or parallel to the surface of the table (see Fig. 70). It is apparent, also, that the axes of the index spindle and attachment spindle are parallel to one another. Therefore, as the table advances, and the blank is turned, the distance between the axes of the index spindle and attachment spindle remains the same. As a result, the periphery of the blank, if milled, is concentric or the lead is 0.
If, then, the spiral head is elevated to any angle between zero and 90° (see Fig. 71), the amount of lead given to the cam will be between that for which the machine is geared and 0. Hence it is clear that cams with a very large range of different leads can be obtained with one set of change gears, and the problem of milling the lobes of a cam is reduced to a question of finding the angle at which to set the head to obtain any given lead.
In order to illustrate the method of obtaining the correct angle, drawings of two cams to be milled, and data connected with same, are given in Figs. 72 and 73.
It is first necessary to know the lead of the lobes of a cam, that is, the amount of rise of each lobe if continued the full circumference of the cam. This can be obtained from the drawings as follows: For cams where the face is divided into hundredths, as those shown: multiply 100 by the rise of the lobe in inches and divide by the number of hundredths of circumference occupied by the lobe. For cams that are figured in degrees of circumference: multiply 360 by the rise of the lobe in inches and divide by the number of degrees of circumference occupied by the lobe. Taking Fig. 72 for example, we have a cam of one lobe which extends through 91 hundredths of the circumference and has a rise .178". Then 100×.178"91=.1956 of lobe or .196", which is near enough for all practical purposes.
Fig. 72
As a .196" lead is much less than .67", which is the shortest lead[1] regularly obtainable on the milling machine, (see Table of Leads, pages 229 to 247), the change gears that will give a lead of .67" may be used, and then the angle of the head can be adjusted so that a lead of .196" will be obtained on the cam lobe with these change gears. The rule for this is:
Divide the given lead of the cam lobe by a lead obtainable on the machine, and the result is the sine of the angle at which to set the head.
Continuing the calculation for the lobe of the cam in Fig. 72, we therefore have: .196".67=.29253
Hence, .29253 is the sine of the correct angle. Turning to the Table of sines and cosines on pages 300 to 308, we find that .29253 is very 
Fig. 73
near .29265, which is the sine of an angle of 17° and 1'. As the spiral head is not graduated closer than quarter degrees, it will be satisfactory to elevate the head just a hair over 17°; then, with the gearing for a lead of .67", a cam with a lead of .196" will be obtained.
The minute errors between the actual lead .1956" and .196", and in the sines and angles of this calculation can be safely ignored, as it is not possible in practice to work very much closer than we have outlined.
The portion of the periphery of the cam from 91 hundredths to zero, represents a clearance of the cutting tool prior to the beginning of the throw. It is usually milled to a line, or drilled, broken out, and filed.
In Fig. 73, we have a cam with two lobes, one, A, having a rise of 2.493" in 47 hundredths, and the other, B, having a rise of 2.443" in 29 hundredths. On cams such as this, where it is necessary to remove considerable stock, it is usually the practice to first outline the approximate shape of the lobes on the blank and drill and break off the surplus stock.
Following the same method of figuring to find the lead of the lobes on this cam, we have: lead for lobe A, and lead for lobe B.
Where there are two or more lobes on a cam, the machine is geared for a lead slightly longer than the longest one required, which in this case is 8.424", then the other lobes are milled without changing the gears. Referring to the Table of Leads, we find a lead of 8.437", which is slightly larger than 8.424". This gearing is, therefore, accepted, and it is required to find the sine of the angle at which to set the head for lobe B.
sine of angle at which to set head. Looking at a table of sines and cosines, .99846 is found to be the sine of an angle of 86° and 49'. The head is, therefore, set at a trifle over 8634 °.
When lobe B has been milled, the head is set for lobe A.
sine of an angle at which to set head. Referring again to the table of sines and cosines, we find that .62865 is very near to .62864, which is the sine of an angle of 38° and 57'. The head is, therefore, set slightly under 39° for this lobe.
The other portions of the periphery of this cam are formed up either by filing to a line before the blank is put on the milling machine or by milling to the line after the lobes have been formed.
Whenever possible, the job should be set up so that the end mill will cut on the lower side of the blank, as this brings the mill and table nearer together and makes the job more rigid. It also prevents chips from accumulating, and enables the operator to better see any lines that may be laid out on the face of the cam.
When the lead of the machine is over 2 inches the automatic feed can be used, but when the lead is less than 2 inches the job should be fed by hand, with the index crank, as shown on page 187.
By the use of the calculations just given, we have compiled tables on pages 248 to 299 that give a wide range of leads from to 20" that can be obtained with the spiral head in the manner described. These tables will be found useful, as they give all data and settings without the necessity of figuring.
Graduating. Another use to which the milling machine may be put is that of graduating flat scales and verniers.[2] It is possible to obtain very accurate results, and when required, odd fractional divisions can be easily spaced.
This operation requires the use of the spiral head and a single pointed graduating tool which is held stationary in a fly cutter arbor, mounted directly in the spindle, or can be fastened to the spindle of a vertical milling or rack cutting attachment. The scale to be
Fig. 74
graduated is clamped to the surface of the table parallel to the table T slots. No power is required for the operation, as the lines are cut by moving the table transversely under the point of the tool, and this can be easily done by hand. The spiral head spindle is equal-geared to the table feed screw as shown in Fig. 74, and indexing for the divisions required is accomplished by means of the index plates, the index crank being turned in the usual manner for each division.
It has already been explained that one turn of the index crank moves the spiral head spindle 140 of a revolution, and if equal gearing is employed between this spindle and the table feed screw, the feed screw will likewise make 140 of a complete revolution. The lead of the feed screw being .25", it is apparent that one turn of the index crank will advance the table an amount equal to .25" × 11/40, or .00625".
Suppose it is required to graduate a scale with lines .0218" apart. Now, if one turn of the index crank moves the table a distance of .00625", it will take more than one turn to move the table a distance of .0218". Hence,
Taking the remainder, .00305", and referring to the tables on pages 318 to 320, we find that it is very near .0030488, which is the distance the table will be moved by using the 41 hole circle in one of the index plates furnished and indexing 20 holes. The error between the actual remainder and the amount given in the table is so small that it can be safely ignored.
Therefore, to graduate a scale with divisions .0218 of an inch apart, an index plate having a 41 hole circle would be used and the crank would have to make three complete turns and then be advanced 20 holes in the 41 hole circle for each division.
It should be remembered in graduating that care must be exercised to prevent backlash between the index crank and table feed screw. To this end, the crank should always be turned in the same direction.
If required, the ratio of gearing between the spiral head spindle and the table feed screw can be changed, but this complicates the operation somewhat and should be resorted to only when it is impossible to get accurate enough results with the method described. Upon referring to the tables on pages 318 to 320 and noting the extreme fineness in divisions that it is possible to obtain, it is apparent that there is little occasion to change the ratio of gearing.
Accurate graduating can also be done by using scales and verniers such as illustrated and described in Chapter V.
Illustrations of cam cutting, and many miscellaneous milling operations will be found on the following pages, and a careful study of the cuts and descriptions may be of value to the reader.
Cutting a Cylindrical Cam, Using Cam Cutting Attachment
For cutting a cylindrical cam, the head is bolted to the bed parallel to the table and the cam blank is supported on an arbor mounted on the attachment centres and dogged to the spindle. The table is raised to a point that brings the attachment centres at the same height as the axis of the spindle.
A spiral end mill is used for this operation and the necessary movement to feed the work is obtained from the attachment, the table remaining clamped in one position.
This view of the attachment shows very clearly the former on the outer end of the head.
Cutting a Face Cam, Using the Cam Cutting Attachment
In this operation the head of the attachment is bolted to the bed at right angles to the table and the cam blank is fastened to the attachment spindle by means of a bolt. A peripheral cam would be milled in the same manner. The necessary rotative movement is obtained by hand feed, and the longitudinal movement to give the proper lead and shape to the cam is produced by the cam former and the mechanism of the attachment, as described in Chapter V.
A spiral end mill is used. The machine table remains clamped in one position.
Milling a Cam, Using Spiral Head and Vertical Spindle Attachment
The cam blank is mounted on an expansion arbor inserted in the taper hole of the spiral head spindle.
Suitable change gears are selected to give the approximate lead and the spiral head is elevated to obtain the exact lead; the vertical attachment is then set to bring the end mill parallel with the axis of the cam. Where such short leads as this are being milled, there is great stress brought upon the spiral head gearing in attempting to use the automatic feed. For this reason the extended crank is fastened over the regular index crank and the job is fed by hand.
Milling Screw Machine Cam, Showing Use of Extension for Spiral Head
This shows the milling of a cam of long leads where the blank must be cut well up to the axis in one place. It is impossible to bring the spiral head spindle and the vertical attachment spindle near enough together to accomplish this deep cut when the spiral head is located in its usual position at the end of the table. The extension for the spiral head is designed to overcome this difficulty, and by using it the spiral head is located some distance in from the end of the table.
The cam in this case has three lobes, each having a different lead. Change gears to mill the longest lead are selected and then the angles of elevation of the head and attachment are changed to obtain the shorter leads while using the same change gears.
Milling Slot in Bushing, Using High Speed Milling Attachment
This operation furnishes a good illustration of the use of the high speed milling attachment. The end mill is only 38'' in diameter, and where such small mills are used, it is necessary to run them at much higher speeds than are ordinarily obtainable on the machine, otherwise the finest feeds, either by power or hand, present material to the cutter faster than the teeth can remove it, and as a result, there is constant danger of breaking the mill. With the high speed attachment, the machine spindle speeds are multiplied so that suitable speeds to combine with the available feeds are obtainable.
The bushing being slotted is fastened in the vise at a proper height to bring the slot central.
Milling Bearing Surfaces and Splitting Ring
This operation presents an example of light gang milling on work of an interesting character. The ring is required to have two flat bearing surfaces, one at each side of the projection on the top, and to be split midway between these bearings. All three operations are performed simultaneously by the method shown.
The ring is fastened to a knee by means of a nut and large washer in the centre, and clamps at each side prevent the piece from opening when cut through. When these pieces are milled in quantities a fixture is employed to hold them.
Two side milling cutters and a slitting saw comprise the gang.
Milling Bolt Heads
The illustration above shows a method of milling the heads of square and hexagonal bolts, using a chuck on the spiral head spindle for clamping the work. It also furnishes a good example of the use of a pair of side milling cutters as "straddle mills." Two sides are finished at a cut, therefore completing a square bolt head with two cuts and a hexagonal one with three cuts.
In indexing the work, the worm of the spiral head is thrown out of mesh and the divisions are obtained from the rapid index plate on the spindle nose.
As the material is of wrought iron, oil is used in cutting.
Milling Angle on Block, Using Universal Milling Attachment
This operation is given chiefly to illustrate a use of the Universal Milling Attachment. This attachment may be set in a vertical, horizontal, or angular position without removing any part of it from the machine. Thus the opposite side of the piece of work shown can be milled without removing it from the vise. The table is simply moved to the left and the head of the attachment is swung to the required angle on the opposite side of the vertical.
In this manner both sides are milled so that they are exactly parallel to one another.
Milling Angular Gib, Using Compound Vertical Spindle Milling Attachment
Angular cutters are not always at hand that will produce the proper angle on angular strips, gibs, etc., and when this is the case, the value of a Compound Vertical Spindle Milling Attachment can be appreciated. This attachment can be swung to mill a wide variety of different angles, using an ordinary end mill. It can be used to mill an angle on a long gib, similar to that shown above, or the head can be removed, turned quarter way around and put back in place, and used to mill an angle on a piece where, for some reason, it is advantageous to feed the table transversely.
Milling Clutch Teeth
This operation is very similar in the way it is set up to the one of Milling Bolts previously described. The character of the cut, however, is lighter and the arbor is supported at the outer end on a centre, whereas in the other operation, the end of the arbor runs in the arbor yoke bearing. A cutter of special form is used, and one tooth is finished at each cut, the cut beginning at the outside of blank and finishing in the centre.
Indexing in this case is accomplished with the regular index plates and crank as the number of teeth required cannot be indexed with the plate on the spindle nose.
Milling End Teeth in End Mill
When it is required to mill end teeth in an end mill, it may be done as shown in the illustration above.
The mill is held by its shank in a collet that is inserted in the spiral head spindle. The spiral head is adjusted to an angle to give the correct form to the teeth.
An angular cutter is used and the table is fed longitudinally. Indexing is accomplished with the index plates and crank in the usual way.
Oil is used, as the material of the end mill is tool steel.
Milling Squares for Wrench on Reamer Shank
A reamer of the type illustrated is necessarily rather long and cannot be accommodated on centres as a shorter piece would be. It is, therefore, passed through the hole in the spiral head spindle and is clamped in the chuck, while the wrench end is supported by the foot-stock centre.
An end mill is used and the work is fed vertically. To prevent longitudinal movement of table, the small clamping lever shown on the front of the saddle is set up. Where there are many pieces to be done, a more permanent method of fixing the table is by means of stops that fasten on to the V bearing at the bottom of the table and come against the side of the saddle.
Milling Tenon on Collet
A taper plug having a centre hole at the large end is driven into the hole in the collet, which is then mounted on the spiral head centres. A dog on the taper plug locks the collet to the spiral head spindle.
An end mill is used and the cutting is done with the teeth on the periphery. The rapid index plate is used to index the work and the table is fed longitudinally.
The table feed trip dog is set to insure milling both sides to the same length.
If a quantity of this work is to be done, formed straddle mills would be employed with an entirely different arrangement.
Milling Flutes in Taper Reamer
There are times when a shop requires a reamer of special size that cannot be procured readily, and in such cases one can be turned up and the flutes cut in the manner shown above. The spiral head is set at the angle of taper and the foot-stock centre is adjusted to correspond with it. The reamer blank is then mounted on the centres and dogged to the spiral head spindle.
A stock cutter, known as a reamer fluting cutter, is used and the table is fed longitudinally.
The procedure is the same for milling a straight reamer, except that the spiral head and foot-stock are set at zero.
Cutting a Spiral with End Mill
When a spiral slot with parallel sides is required an end mill should be employed and the job set up as shown above.
The spiral head centres are brought to a level with the centre of the machine spindle.
The table is at right angles to the spindle and the angle of the spiral is obtained by the combination of change gears used.
Either right or left-hand spirals can be cut in this way by simply leaving out or interposing an intermediate gear in the train of change gears.
Cutting Slots in Screw Machine Tool, Using Slotting Attachment
The screw machine tool is held by its shank in a vise, and the slotting attachment is set at an angle so as to give the proper clearance to the cutter that is intended for use in the slot. A hole is drilled for starting the slot.
In slotting work, all necessary movements of the table are made by the hand feed.
The swivel vise is very useful in connection with the slotting attachment, for the work can be swung to any angle or indexed, if it is desired to make a special shaped slot.
Slotting Square Hole in Extension Wrench
In this operation the piece of work is too long to be set in a vertical position; it is, therefore, passed through the spiral head spindle and is clamped in the chuck. The slotting attachment head is then set so that the tool moves in a path parallel to the top of the table.
The ability to swing the head from a vertical to a horizontal position is one of the features of the B. & S. attachment.
The piece of work is indexed by means of the rapid index plate. All necessary movements of the table are made by hand.
Milling Flutes of Twist Drill
This operation is very similar to that of cutting a spiral gear. The drill blank is mounted on the spiral head centres and fastened to the spindle with a dog. The spiral head is geared for the required lead and the necessary angle is obtained by swinging the swivel table.
As the character of the cut is heavy, the arm braces are employed to give additional rigidity to the arbor. A stock cutter of special form, known as a twist drill cutter, is employed and oil is used in cutting.
More complete information on this subject can be found in Chapter IV.
Sawing Flat Stock
When it is necessary to saw a piece of flat stock, it may be strapped directly to the table in a position so that the line where it is to be cut comes over a slot.
A metal slitting saw is used to split the piece and the table is fed in the same direction to that in which the saw revolves. This prevents the tendency to raise the work from the table and wedge the cutter; also for the cut to run out of a straight line. In feeding the table in this manner, every precaution should be taken to eliminate backlash from the feed screw.
Milling Semi-Circle in Top of Spiral Head Base
The casting is clamped directly to the table, as clearly shown in the illustration, and the knee is raised so that the top of the piece is in a line with the axis of the cutter.
A shell end mill is used and the table is fed transversely, bringing all the cutting upon the end teeth of the mill.
When a mill is used in this manner, it is well to grind the teeth on the periphery a little smaller at the back end, as this has a tendency to prevent chattering.
Boring Holes in Jig
The use of a scale and vernier in connection with a boring bar, boring holes where accurate spacing is required, is shown in this operation. Finer adjustments can be obtained in this way than are possible using the dial on the longitudinal hand feed screw.
The work is strapped to the table, and the boring bar, which is in reality a kind of fly tool, is held in a collet inserted in the spindle. Scales and verniers can also be furnished for the transverse and vertical movements of Brown & Sharpe milling machines.
Milling Curved and Flat Surfaces at one Setting of Work, Using Vertical Spindle and Circular Milling Attachments
A combination of a vertical spindle and circular milling attachment is shown in this operation. With these two attachments, practically the same variety of work can be done as on a vertical spindle milling machine of equal capacity.
The job being done consists of milling a flat surface on the top of a piece and a curved surface at the end of it. The piece is set over a bushing inserted in the centre of the circular milling attachment table. The work is fed in a circular path by means of the hand-wheel, and when the flat cut is finished, the machine table is raised for milling the curved surface, but the work is not disturbed.
With a vertical spindle milling machine, only the circular milling attachment is needed.
Planing on a Milling Machine
This illustration shows a comparatively unusual operation on the milling machine. Planing can be done on any milling machine by clamping the spindle and moving the table by hand; but on our constant speed drive machines, the spindle can be clamped and the power feeds for longitudinal movement of table are still available.
The special device for clamping the spindle consists of a split ring that fits on the nose of the spindle, over which a bracket is clamped to the column. A bevel sleeve contained in the bracket closes the split ring on the spindle when the three bolts are tightened.
A fly tool is used, and if power feed is utilized, the table is usually fed at its fastest feed. The work is fed upward or transversely by means of the vertical transverse or hand feeds—often both are employed.
Drilling Holes in Bushing
A method of drilling holes in round pieces of work where they are required to be exactly spaced is shown in this operation.
The bushing is held in the spiral head chuck and is indexed in the regular way, or with the rapid index plate, if the number of holes required can be obtained by the latter.
An ordinary twist drill, held in a spring chuck, is employed and the table is usually fed by hand. A collet can be employed for a drill having a taper shank.