American-School-Tool-Making-book
 

pg 128-129 TOOL-MAKING 
    what according to the nature of the work to be done, but for general shop use the numbers estimated in Table VI will be found satisfactory : For most work it is desirable to have the faces of the teeth radial, Fig. 190. However, when milling cutters are made to run in the direction of the feed or on to the work instead of against it, the teeth should be given a negative rake (cut ahead of the center), as shown in Fig. 191, as this has a tendency to keep the piece being milled from drawing toward the cutters. For cutters to be used in sink-ing a semicircular slot in such a piece of work as is shown in Fig. 192, the teeth should be cut back of the center. When cutting the teeth, it is necessary to use a cutter that gives sufficient depth of tooth to provide a receptacle for chips, and also gives a form that supports the cutting edges. A cutter may be used that will produce an angle of about 50 degrees between the face and the back of the tooth, as shown at A in Fig. 190. The cutter should cut deep enough to 

Fig. 192. Form of Cutter for Semicircular Slot 
fi 

Section 11.17 Fig. 193. Form of Cutter Used for Copper 
leave the lands about -31-2- inch in width at the cutting edges. Saws for Copper Work. Metal slitting saws for use on copper do not work well if made the same as those used on steel and most other metals. The face of the tool should have a rake of from 8 to 12 degrees, and the sides of the tool given clearance, as shown in Fig. 193. As such saws are usually made thicker at 
the circumference than toward the center hole, there is little trouble from their binding the work. The pitch of saws for use on copper should be considerably coarser than for those used on the harder metals. For saws of 
TOOL-MAKING 
129 
ordinary size, the teeth should be spaced nearly or quite 1 inch apart; for instance, a saw 4 inches in diameter should have 12 teeth. Grinding the Hole to Size. it is customary to ream the holes in milling cutters to size, and if the cutter contracts in hardening, the holes are brought to size again by lapping with a lead or cast-iron lap, by means of oil and emery. This operation does not, however, provide for the enlarging of the hole. While expansion is an unusual occurrence, it does sometimes happen, and, as a con-

Fig. 194. Typical Set-Up for Grinding a Cutter Courtesy of Norton Grinding Company, Worcester, Massachusetts 
sequence, the cutter does not fit the milling machine arbor and cannot do as good or as much work as it should. The necessity of having a correct fit on the milling machine arbor makes it advisable to ream the hole of the cutter with a reamer about .005 inch under the size of the arbor, and to finish by grinding after the cutter is hardened. When grinding the hole to size, the cutter may be held in a chuck and ground with a small emery wheel, using the internal grinding attachment as shown in Fig. 194. This attachment is so 'designed that it may be swung out of the way when gaging the size of the hole, Fig. 195. 

pg 130-131 TOOL-MAKING 

130 TOOL-MAKING 
Grinding Shoulders. After grinding the hole to size, it is advisable to grind the shoulders on each side of the cutter, straight and true with the hole, in order to prevent any possibility of springing the milling machine arbor because of untrueness on the part of the cutter, and to prevent any possibility of the cutter running out of true. The shoulder, or boss, referred to is shown in A, Fig. 190. 

Fig. 195. Gaging Size of Hole in Cutter after Grinding Courtesy of Norton Grinding Company, Worcester, Massachusetts 
There are two methods of grinding the shoulders. By one method, the outer shoulder and the hole are ground at the same set-ting; if this is done properly, this shoulder will be true with the hole. The chuck is then removed from the grinder, and a faceplate having an expanding plug is put in its place. The shoulder that has been ground is placed against the faceplate, with the expanding plug in the hole of the cutter. The other shoulder may be ground after the plug is expanded until the cutter is held rigidly in place against the faceplate, which should run perfectly true. 

TOOL-MAKING 131 
By the other method, both shoulders are ground while on an arbor, which is necked down each side of the cutter, Fig. 196, 
Fig. 196. Cutter Blank on Special Arbor for Grinding allowing the wheel to traverse the whole length of the shoulder but not cut into the arbor, as when an ordinary mandrel is used. 

Fig. 197. Cutter in Position for Grinding Teeth Courtesy of Cincinnati Milling Machine Company, Cincinnati, Ohtio Grinding Teeth. In order to get the best results from a milling cutter, it is necessary to use a form of grinder having some means of 

          132-133 TOOL-MAKING 

132 TOOL-MAKING 
properly locating each tooth as it is presented to the wheel. The usual arrangement is a finger adjustable to the proper height to produce the required amount of clearance, which is about 3 degrees, as shown at B, Fig. 190. With this amount of clearance, the cutter works freely and retains its edge; if more clear-ance is given, the cutter is likely to chatter, and the edges of the teeth will become dull rapidly. Fig. 197 shows a cutter in position for grinding the teeth; it will readily be seen that the tooth being ground rests on the centering gage E, which can be adjusted to give any desired amount of clearance to the tooth. For grinding the teeth on the side of a milling cutter, a small emery wheel may be used in order to get the necessary amount of clearance with-out touching the tooth next to the one being ground. If a grinder is used which will take a cup wheel, Fig. 198, and whose table can be turned to bring the cutter in the position shown in Fig. 199, a form of clearance is given which is more satisfactory than a clearance ground with a small wheel. With the cup wheel the line of clearance is straight, while with the small plain wheel it is hollowed out, and as a consequence the cutting edge is weak. 

Fig. 198. Section of Cup Grinding Wheel 

Fig. 199. Grinding Milling Cutter with Cup Wheel Courtesy of Cincinnati Milling Machine Company, Cincinnati, Ohio 
Side Milling Cutter. Cutting Teeth. The form of cutter shown in Fig. 190 is known as a side milling cutter. When cutting teeth on the sides, it is necessary to put the cutter on a plug whose upper 

    pg 133  TOOL-MAKING 133 
end does not Project much above the top face of the cutter; this plug may be made straight and held in the chuck on the end of spindle in the spiral head. Such a plug is shown in Fig. 200, inserted in the cutter. If many cutters are made with teeth on the sides, it is advis-able to make an expanding arbor. Fig. 201. whose shank fits the taper hole in the spin-dle of the spiral head. When milling the teeth on the sides, the index head must be in-clined a little so that the side of the mill will stand at a small angle from the hori-zontal, in order that the lands of the teeth may be of equal width at each end. The amount of this inclination can-not readily be computed. It is formed by cutting first one tooth, leav-ing the cut somewhat shallow, then turning to the next tooth. After cutting the second tooth, the change in inclination will be apparent. Hardening. When the teeth are cut and the burrs removed, the diameter and length of the cutters may be stamped as shown in Fig. 190. The cutter is now ready for hardening. To harden success-fully, it is necessary to have a low, uniform red heat; the teeth must be no hotter than the portion between the hole and the bottom of the teeth. If held toward the light, there should be no trace of black in the interior of the cutter. When a uniform heat, no higher than is necessary to harden the steel, has been obtained, the cutter should 

Fig. 200. Milling Cutter Mounted on Plug 

Fig. 201. Typical Expanding Arbor 

be plunged into brine from which the chill has been removed, and worked around rapidly in the bath until the singing has ceased. It should then be removed from the brine and immediately plunged into oil and allowed to remain there until cold. When cold, the 

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  page 134-135  TOOL-MAKING 

134 TOOL-MAKING 
cutter should be taken from the oil and heated sufficiently to prevent cracking from internal strains, then brightened, and the temper drawl to a straw color. Spiral Milling Cutters. It is customary in most machine shops to make all milling cutters of more than 2-inch face with teeth cut spirally as in Fig. 202. The amount of spiral given the teeth varies in different shops and on different classes of work. The object of spiral teeth is to maintain a uniformity of cutting duty at each instant of time. With teeth parallel to the cutter axis.. the tooth, on meeting the work, takes the cut its entire length at the same instant, and the springing of the device holding the work and of the cutter arbor causes a jump to the work. If the teeth are 

Fig. 202. Milling Cutter with Spiral Teeth Courtesy of Brown and Sharpe Manufacturing Company, Providence, Rhode Island 
cut spirally, the cut proceeds gradually along the whole length of the tooth; and after it is started, a uniform cutting action is maintained, producing smoother work and a truer surface, especially in the case of wide cuts. Milling cutters may be cut with either a right- or a left-hand spiral or helix, although it is generally considered good practice to cut a mill having a wide face with a spiral that will tend to force the cutter arbor into the spindle rather than to draw it out; then, again, it is better to have the cutting action force the solid shoulder against the box, rather than draw the adjusting nut against the box. Where two very long mills are used on the same arbor and it is found necessary to cut them with a quick spiral, one cutter is some-times made with a right-hand spiral and the other with a left-hand 
TOOL-MAKING 
135 
spiral, in order to equalize the strain and to reduce the friction result-ing from the shoulder of the spindle pressing hard against the box. Special care should be taken in cutting spiral milling cutters to see that the work does not slip. When a cut has been taken across the face of a cutter, it is best to lower the knee of the milling machine, thus dropping the work away from the mill while coming back for another cut; the knee can then be raised to its proper posi-tion, which is determined by means of the graduated collar on the elevating shaft of the machine. As it is important that the face of the cutting tooth be radial and straight, it will be found necessary to use an angular cutter of the form shown in Fig. 203, since cutters of this form readily clear the radial face of the cut and so remain sharp longer and produce a smoother surfact to the face of Fig. 2f0o3r. srAirnagluW;IFutter the tooth than an angular cutter of the form used for cutting teeth which are parallel to the cutter axis. The angular cutters for spiral mills are made with either 40 degrees, 48 degrees, or 53 degrees on one side, and 12 degrees on the other. By setting the cutter, as shown in Fig. 203, so that the dis-tance A is one-twelfth the diameter, the face cut by the 12-degree side of the angular cut-ter will be nearly radial for the usual propor-tions. The setting for cutting the teeth of a spiral cutter must be made before turning the spiral bed to the angle of the spiral. Nicked Teeth. Spiral cutters with nicked teeth, Fig. 204, are especially adapted for heavy milling. As the chip is broken up, a 

Fig. 204. Spiral Cutter with Nicked Teeth Courtesy of Becker Milling Machine Company, Hyde Park, Massachusetts 

137-137 TOOL-MAKING 
If many formed mills are to be made, it is advisable to procure or make a machine specially designed for relieving—backing off—the teeth. As such machines are heavy and rigid, large cutters may be relieved and a smooth cut obtained, which is not possible with a light machine. Backing-Off Lathe Attachments. Although this style of cutter can be made to better advantage in a shop equipped with machinery designed especially for this class of work, an ordinary engine lathe 

Fig. 220. Balzar Backing-Off Attachment 
can be converted into a backing-off lathe for relieving or backing off the cutters. There are several commercial devices for the work : one comparatively inexpensive fixture is known as the "Balzar" backing-off attachment, Fig. 220; another arrangement consists simply of an eccentric arbor operated by a hand lever; or, a stud may be screwed into the faceplate of a lathe and the cutter placed on this stud 136   

 

p

          pg 136-137

 

page 148 TOOL-MAKING  Locating Cutter Tooth for backing off tools on faceplate.           136 TOOL-MAKING 
much heavier cut can be taken than would be possible with an ordi-nary cutter. The nicking may be done as follows: An engine lathe is geared to cut a thread of the required pitch—two threads to the inch will be found satisfactory—and   with a round-nosed tools inch wide,   a thread is cut of a depth that will   not grind out before the teeth become too shallow to allow further grinding. This thread should be cut before mill-ing the spaces to form the teeth. Milling Cutters with Interlocking Teeth. When two milling cutters of an equal diam-eter are to be used 'on the same arbor in such a manner that the end of one cutter is against the end of the other, the corners of the cutting teeth are likely to break away, leaving a pro-jection—or fin—on the work, as shown in Fig. 205. In order to overcome this, part of the teeth are cut away on the sides of the cutters; that is, a tooth is cut away on one cutter, and the corresponding tooth on the other cutter is left full length to set into the recess formed by the cutting away of the tooth. In some shops it is customary to cut away every other tooth; while in others, two, three, or four teeth will be cut away and an equal number left. Fig. 206 represents a pair of mills hav-ing every other tooth cut away, while Fig. 207 represents a pair having four teeth cut away. In order to cut away the teeth to make a cutter with interlocking teeth, the cutter should be placed on a plug or an expanding arbor, as described for milling teeth on the sides of side milling cutters. By means of a milling 
Fig. 205. Badly Made Mill 

Fig. 206. Pair of Mills with Alternate Teeth Cut Away Courtesy of Brown and Sharpe Manufacturing Company, Providence, Rhode Island 

Fig. 207. Interlocking Cutters with Four Teeth Cut Away Courtesy of Union Twist Drill Company, Ahtol, Massachusetts 
TOOL-MAKING 137 
cutter having the proper width, the teeth may be milled away, although, in the case of a cutter having several teeth cut away, Fig. 207, it is well to use a narrow cutter, and after taking one cut, to turn the index head so that the next tooth is in position. This should be continued until the desired number of teeth have been cut away, after which the index head should be turned to pass over the required number of teeth, and the operation repeated. It is necessary, when making cutters with interlocking teeth (sometimes called dodged teeth) that the milling be deep enough to prevent the corresponding tooth on the other part of the cutter from 
ing the bottom of ecess. The parts of cutter should bear ist each other on shoulders, or hubs. Cutters for Milling >. An excellent form utter to be used for work as milling can be made as rn in Fig. 208. This is less expensive L one having interlocking teeth and answers the purpose as well. necesssary to make an eccentric mandrel of the design shown in 209, having the eccentric centers on opposite sides of the regular ers. The two pieces which make the cutter should be cut from bar long enough to finish the thickness of the heaviest part 
strik the r1 the agair the 
Slots of cu such slots ohm form than It is Fig. cent the 
AA the 
Ing. fore of t 

Fig. 208. Milling Cutter for Slots 
49 
Fig. 209. Eccentric Mandrel for Slot Cutters 
, Fig. 208. The hole is made 2-6 inch smaller than finish size, outside surface turned off, and the pieces annealed. After annealing, the hole is made the size desired for grind-One of the pieces is then placed on the eccentric mandrel, ed on until the side that is to be beveled is exactly in the center he mandrel. The side B may be machined with the mandrel 

ppage 144 TOOL-MAKING 
     If many formed mills are to be made, it is advisable to procure or make a machine specially designed for relieving—backing off—the teeth. As such machines are heavy and rigid, large cutters may be relieved and a smooth cut obtained, which is not possible with a light machine. Backing-Off Lathe Attachments. Although this style of cutter can be made to better advantage in a shop equipped with machinery designed especially for this class of work, an ordinary engine lathe 

Fig. 220. Balzar Backing-Off Attachment 
can be converted into a backing-off lathe for relieving or backing off the cutters. There are several commercial devices for the work : one comparatively inexpensive fixture is known as the "Balzar" backing-off attachment, Fig. 220; another arrangement consists simply of an eccentric arbor operated by a hand lever; or, a stud may be screwed into the faceplate of a lathe and the cutter placed on this stud in a position that allows the teeth to be given the necessary amount of clearance. 

TOOL-MAKING 145 
When backing off the teeth of cutters whose faces do not exceed one inch in width, the Balzari backing-off fixture can be used to advantage. This device is held between the centers of a lathe in, 

Fig. 221. Special Arbor for Backing Off 
the ordinary manner, the backing off being such that the cutter can be ground without alteration of shape. The tool is so constructed that it is only necessary to place the cutter upon the arbor in the ordinary way. Place the arbor on the lathe centers as shown, start the lathe, and feed the forming tool in by the cross-feed screw in order to take the desired cut, in the same manner as in plain turning. The ratchet connected with the arbor and actuated by the pawl, contains ordinarily 36 teeth, and the stroke can be set to back off a cutter with 9, 12, 18, or 36 teeth.

Backing Of by an Eccentric Arbor. An arbor may be made having a pair of centers located to give the cutter tooth the required amount of clearance; such an arbor is shown in Fig. 221. The eccentric centers are shown at the sectional portions at the ends. The amount of eccentricity depends somewhat on the size of the cutter to be backed off, but for cutters not exceeding 4 inches in diameter, from to / inch will give excellent results. The screw at the end of the arbor should be of a fine pitch, about 12 threads per inch for arbors one inch in diameter. The object in 
ifiril 1.m  

".4 
Fig. 222. Eccentric Arbor fcr Backing-Off Cutter cutting a fine-pitch thread is that the cutter, being backed off, can be hold more securely with the same amount of force exerted in tightening the nut; again, the depth of the thread is not so great as 

 

TOOL-MAKING  page  148-149 

page 148 TOOL-MAKING 
     brought down upon the carriage, the tooth of the cutter is brought down upon the sheet metal, and the nut is tightened. The tooth to be backed off is the one below that set to the thickness of the strip above the tool. The object in raising the tooth a given distance above the face is to prevent striking the tool at the end of the stroke. This operation must be repeated for the setting of each tooth before backing off. The forming tool is fed by means of the cross-feed screw; a tooth is backed off nearly the desired amount, leaving a little for a finish cut; the tool is withdrawn, the nut 

emill itill  
III Fig. 227. Method of Locating Cutter Tooth for Backing Off loosened, and the cutter turned on the arbor to bring the next tooth in position to be backed off, this operation being repeated until all the teeth are backed off alike. The amount of backing off must be determined by the cross-feed stop or by a graduated dial on the cross-feed screw. After the roughing cut has been taken on all the teeth, the forming tool should be sharpened by grinding or by oil-stoning, and the finish cut taken on the teeth. Backing Of by Stud in Faceplate. Another method of backing off cutter teeth is shown in Fig. 228. A stud is screwed in the face-plate of a lathe near the outer edge, as shown. The cutter, which must be a fit on the stud, is claniped by means of the nut. The finger 

TOOL-MAKING 149 
     A is movable in the slot in the stationary block B, which is so located on the faceplate as to bring the tooth. to be backed off into its proper location, and to keep it from turning during the operation. The forming tool is fed in gradually until the tooth is formed. The finger is then disengaged from the space in the cutter, which is revolved by means of the set screw until the next tooth is in position. Each tooth is machined separately; that is, the forming tool is fed in the required distance for each tooth when it is in position, the cutter is turned until the next tooth is in position, and the process repeated until each tooth has been backed off. In backing off cutters in this 

Fig. 228. Set-Up for Backing Off Cutter on Faceplate device, it is necessary to cut the notches (the spaces between the teeth) somewhat wider than the teeth. General Directions for Backing Off. When backing off the teeth for clearance by any of the means described, it is first necessary to form the blank, then to gash it or to cut the notches as described; then to back off the teeth. After backing off, it is necessary to mill the face of the tooth back 322 inch or so, to cut away the "jump", as it is termed, caused by the forming tool drawing in a trifle when it first strikes the edge of the tooth. ' Cutters of this description are sharpened by grinding on the face of teeth, as shown in Fig. 229. Milling Cutters with Threaded Holes. It is often necessary to make milling cutters with threaded holes. This happens in the case 

 

TOOL-MAKING  page  150-151   

150 TOOL-MAKING 

of small angular cutters, and in many styles of cutters for use on profiling (edge milling) machines. The general instructions given for making the other forms of cutters apply to those with threaded holes, except that instead of 
TOOL-MAKING pg 151 

trifle, say one thread. This allows the outer end to be squared up without mutilating the threads on the arbor. The reason for using the taper end of the arbor when squaring the first end of the cutter is that the shoulder is true with the thread in the cutter. After squaring this shoulder, the cutter blank may be removed and placed on the opposite end of the arbor with the side that has been squared against the shoulder of the arbor. This method of machining pieces of work having a threaded hole, where it is desirable that the outer surfaces be true with the hole, is applicable to all classes of work. The cutter may be machined to length and shape on the straight end of the arbor. Fly Cutters. The simplest form of milling machine cutter is known as a fly cutter. It has only one cutting edge, but is particu-

Fig. 229. Method of Grinding Formed Cutters reaming the hole to a given size, the thread is cut with a tap of the proper size and pitch, or it is chased in the lathe. After threading, the cutter should be screwed on to a threaded arbor. Fig. 230 shows an arbor of this description. The end A is threaded slightly taper-

Fig. 230. Typical Threaded Arbor ing, for short cutters about .002 inch in one inch of length. On the taper end of the arbor, a thread should be cut of a size that will not allow the cutter to screw on the arbor quite the entire length; that is, the cutter should overhang the threaded portion' of the arbor a 

larly valuable when mak-ing but one or two pieces of a kind for experimental work, and when making and duplicating screw-machine and similar tools of irregular shape. As these cutters have but one cutting edge, they produce work very accurate as to shape, but they cut very slowly and do not last so long as those having more teeth. However, they are used on special work, on account of the small cost of making. It is necessary to hold the cutters in a fly-cutter arbor, Fig. 231. The cutter to be used in a fly cutter arbor may be filed to a templet, giving the necessary amount of clearance in order that the back edge, or "heel", may not drag. If it is desirable to make the impression in the fly cutter with a milling cutter of the regular form, the piece of square steel from which the cutter is to be made may be held in the mill ing machine vise, and the shape cut with the milling cutter. The desired amount of clearance may be given by holding the piece in the vise at an angle of a few degrees. To make a fly cutter from the forming tool, the piece of steel may be held in the fly cutter arbor in such a position that the face is somewhat back of a radial line, as shown in Fig. 232. After hardening, the cutter should be set so that the cutting edge will be radial, and the clearance will be as shown in Fig. 233. 

Fig. 231. Fly-Cutter Arbor 

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   pg-152 TOOL-MAKING 
Another method of getting the clearance for the cutter is to place, the top of the cutter blank as near the arbor as possible, and then to', cut the desired shape. If the cutter is set in the arbor so that it 

Fig. 232, First Step Fig. 233. Fly Cutter in Making Fly Set Radial with Cutter Clearance Provided 

Fig. 231. Simple Method of Getting Clearance on Fly Cutter 
projects from the surface, it will have the necessary clearance, as shown in Fig. 234. A represents the position of the blank while being cut, and B the cutter in position for cutting; as the dotted line shows the circle through which the cutting edge travels, the amount of clearance is apparent. End Mills. This form of milling machine cutter, Fig. 235, is familiarly known as a shank mill, on account of the shank, which in small milling cutters fits into a collet. This collet in turn fits the hole in the spindle of the milling machine; the collet is used to save stock in making the cutters, as otherwise it would be necessary to use steel large enough to make a shank the size of the hole in the spindle of the milling machine. The cutter shown in the figure is what is termed a left-hand mill; if the teeth run in the opposite direction, it is called a right-hand mill. In making a shank, or end mill, of the form shown, stock should be selected enough larger than the cutting end to allow of turning 

Fig. 235. Straight Flute Left-Hand End Mill Courtesy of Becker Milling Machine Company, Hyde Park, Massachusetts off the decarbonized surface of the steel. After the ends have been faced to length, and the roughing chip turned, the cutting end can be run in the steady rest of the lathe, and the center cut away, or 

  pg-153 TOOL-MAKING 
recessed, as shown at the end of the mill. The blank should be re-centered and countersunk, to furnish a center to use in turning the mill to size and shape. The object in cutting the center out as shown is to furnish a cavity for the angular cutter used in cutting the teeth on the end of the mill. Without the recess, it would be impossible to grind satisfactorily. After re-centering the recessed end, the opposite end should be turned to size and milled to thickness, which should be a trifle-11,2 inch—less than the width of the center key slot in the collet. The taper shank should be turned enough larger than finish size to allow for grinding after the milling cutter is hardened ; the cutter end should be turned .010 inch larger than the required diameter ; the portion just back of the cutters should be turned 1-2- inch smaller than 

Fig. 236. Cutter with Weak Teeth 

Fig. 237. Cutter with Well-Formed Teeth 

Fig. 238. Cutter with Especially Strong Teeth 

Fig. 239. Method of Cutting Strong Teeth 
the large end of the shank, or to dimensions, if any are given on the drawings. In order to insure teeth strong enough to resist the strain of cutting, an angular mill should be selected that will give the required shape. In Fig. 236 is shown a form of cutter tooth too weak for actual service, the result of using an angular cutter with a cutting face forming an angle that is too acute with the side. Fig. 237 illus-trates a cutter whose teeth are strong, yet deep enough to be practical; these teeth were cut with an angular mill of smaller angle. Fig. 238 represents a cutter whose teeth were cut with the same cutter used for Fig. 236. The teeth were cut to the required depth first, but this of course left them too thick at the cutting edges A, Fig. 239, and the index head was turned sufficiently to cut the teeth as shown at A, Fig. 238. After the teeth around the circumference of the mill have been cut, the mill should be placed in the collet, and the collet put in the spindle hole in the spiral head to cut the teeth on the end. When 

Fig. 231. Fly-Cutter Arbor 

  

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