Above: Lincoln-Style-Pratt-and-2-Whitney-Milling Machine like the one in my collection. Lincoln Milling Machine Pic Courtesy of Pratt and Whitney Company,       Hartford,  Connecticut : https//antiquemachinery.com/Smithsonian-My-Lincoln-Mill
 

pg-4 
MILLING-MACHINE WORK. § 13 
carry the cutting tools. Each spindle, and hence each cut-ting tool, is usually made to be independently adjustable in relation to the work. In most machines of this class, the work can be moved in a straight line in one direction only. Multispindle milling machines are intended for finishing several surfaces simultaneously, and are usually en-iployed for heavy work only. 1 6. Special milling machines may take any con-ceivable form that will adapt them for the class of work for which they are designed, but no matter in what manner they are constructed, the principles of operation will be the same as those of any regular milling machines. 
CONSTRUCTION OF A Milling MACHINE. 
ESSENTIAL PARTS. 
17. A milling machine consists of certain essential parts, which in some form or other must exist in any of its numerous modifications. The essential parts are the frame, the spindle, the table, the feed-mechanism, and the cutting tool. The function of the frame is the supporting of the spindle, table, and feed-mechanism. The spindle, which by suitable means is revolved in bearings provided for it in the frame, carries the cutting tool. The function of the table is to serve as a support for the work, which may be attached either directly to the table or to holding devices carried by it. The feed-mechanism serves to move the work past the cutting tool ; it may operate directly upon the table, or upon the spindle, or upon both. The function of the cut-ting tool is self-explanatory. 
CONSTRUCTION. 
1 8. The universal milling machine is the most advanced form for general work, and embodies all the features found in other types. For this reason it is here selected and 
§ 13   MILLING-MACHINE WORK. 
described. As far as the universal machines of various makes are concerned, their general arrangement is similar to that of the machine illustrated in Fig. 1; they differ only in the design of the details, which are modified in accordance 
pil 

pg 134 MACHINE SHOP WORK  Cutters and Arbors:
in order that the adaptation of the machine to the cutter may be clearly seen. Cutters are classified according to their form or the use to which they are put, some of the more common types of these devices being as follows: 
1. Slitting 2. Grooving 3. Fluting 4. Straight 5. Angle 6. Double-angle 7. Straight mill 8. Spiral mill 9. Nicked-tooth spiral mill 10. Side mill 
11. Straddle mill 12. Straight end mill 13. Spiral end mill 14. T-slot mill 15. Formed mill 16. Inserted blade 17. Inserted-tooth facing 18. Inserted-tooth surfacing 19. Shell mill 20. Fly or single-tooth cutter 
This classification does not include any of the cutters used in cutting gears, racks, spirals, helical gears, ratchets, sprocket-wheels, 

Fig. 200. Details of Ordinary Milling Cutter 
and similar work, which is usually considered as gear-cutting work. However, ratchet teeth may be cut with an angle cutter; brass gears, with a single-tooth or fly cutter, properly formed; and some others may be applied to a variety of uses, the cutter, in fact, not infre-quently displaying a remarkable adaptability to the varying conditions of work and material. 

MACHINE SHOP WORK 135 

Fundamental Characteristics. The several details of an ordinary milling cutter are shown in Fig. 200.

A is the outside diameter;

B, the thickness (or in mills such as shown in Fig. 201, the length) ;

C, the diameter of the hole;

D, the width of keyway;

E, the depth of keyway;

F, the pitch of the teeth;

G, the top of the teeth or land;

H, the backing-off or clearance, either on the lands or on the side of the cutter;

J, the depth of the teeth;

K, the face of the teeth;

L, the relieving recess made for the purpose of reducing the surface to be ground;

M,the hub.

The direction of revolu-tion is indicated by the arrow. Cutter Arbor. Fig. 202 shows the usual form of cutter arbor, in which A is the taper shank fitting the taper-reamed hole in the milling-machine spindle; B is the flattened portion or tang fitting in the cross-slot and preventing the arbor from turning; C is a nut used in withdrawing the arbor from the hole when it has been forced tightly into it; D is a collar formed upon the arbor, against which loose collars or the cutter itself are forced when placed upon the arbor at E and confined by the clamping nut F. The end G is finished as a 

Fig. 201. Milling Cutter with Spiral Teeth Courtesy of Brown and Sharpe Manufacturing Company, Providence, Rhode Island 

Fig. 202. Ordinary Form of Cutter Arbor 
journal or bearing for an outer support attached to or forming a part of the overhanging arm of the milling machine. In the outer end is drilled and reamed a center hole for a similar purpose. Fastening Cutter in Arbor. Cutters are prevented from turning upon the arbor in any one of four ways—namely, first, by a key in the keyway DE, Fig. 200; second, by being clamped between  

 

pg-144 MACHINE SHOP WORK 

of the cutter; but when using the end of the cutter, it means that the teeth can have no rake, and must scrape rather than cut the work. In order to use a leading spiral on the cutter, the shank must be held positively in the spindle. This usually is accomplished by inserting in a threaded hole at the rear end of the shank, a rod which extends through the hollow spindle and brings up against a collar on the out-side. This can be set up solidly, and all danger of loosening-up of the cutter shank will be avoided. When the cutter is small, as compared with the diameter of the spindle taper, a screw collet may be used, as the friction of the collet will be greater than the tendency of the leading spiral to move the cutter from the spindle. These screw collets are commonly made of machine steel, while the end mills are made from tool steel. The short, steep taper and threaded end are shorter than the long taper shank, resulting in a cheaper cutter. One of the best means for hold-ing small end mills with straight teeth is by the use of spring collets, Fig. 221, which can firmly grasp the straight shank of the cutter. When cutters are to be changed frequently, 

Fig. 221. Typical Spring Collets 
this is a particularly satisfactory method, although it will not answer for roughing cuts where cutters of large diameter are used, as the torque will be too great for the jaws of the collet to prevent turning. An ordinary drill chuck can be held in the spindle by means of a taper shank, and furnish a means of holding straight-shank drills and other small straight-shank tools. A very convenient method of holding certain tools consists in fitting a three-jawed universal lathe-chuck to the threaded nose of the spindle, thus enabling straight-shank tools of large size to be held firmly and accurately. Cutters of any kind are rarely held in chucks on the milling machine, but a large number of other small tools can be held advantageously. 

here 9-15-24

 

46 SHAPER AND SLOTTER WORK. 
CLASSES OF SHAPERS. 
2. Types of Shapers.—The ordinary types of shapers may be divided into column shapers and traveling-head shapers, the distinction being made largely on account of the style of the frame of the tool and the feed. In the column shaper the work is fed sidewise during the return stroke of the tool, while in the traveling-head shaper the head is fed sidewise during the return stroke of the tool. Column shapers may also be divided into two classes, crank-shapers and geared shapers, the division depending on the method of driving the tool. There are also several special types of shapers, or machines belonging to the shaper class, that will be considered after the work of the ordinary shaper has been discussed. 
COLUMN SHAPERS. 
CRANK-DRIVEN SHAPER. 
3. Construction of Shaper.-This class of shaper consists of a column A, Fig. 1, that supports the driving mechanism and the various stationary and movable parts of the machine ; a movable ram B that carries the cutting tool at one end ; and a movable table E to which the work is fastened. The ram B slides in flat bearings formed on top of the column ; at its front end it carries the shaper head D, which gives the down feed. This shaper head is so arranged that it can be swiveled around to make any angle with the top surface of the table. The ram is moved to and fro over the work by the driving mechanism within the column, which is operated by belting from a countershaft to the cone pul-ley J. The length of stroke and the position of the ram with reference to the work are adjustable. The shaper head D carries a tool block H similar to that of a planer. The table E is fastened by bolts to a saddle M, which is gibbed to the cross-rail I and can be moved along it either by hand 

§9 
SHAPER AND SLOTTER WORK. 47 
or by an automatic feed. The cross-rail can be raised or lowered by means of a screw on the vertical slide G, which forms part of the column, and can be clamped to it at any point. The table E usually has a removable vise F fitted to 

FIG. 1. 
it. To assist in supporting the table, a screw jack N is occasionally attached to the base of the machine. The amount of feed for each stroke of the ram can be adjusted by varying the position of a slide that can be locked by the handle L. 
4. Driving Mechanism.—The driving mechanism of the column shaper shown in Fig. 1 is illustrated by the two detailed sections, Fig. 2. A is the column or main frame, B is the ram that carries at the front end the swivel piece C. 
 

pg 134-135 MACHINE SHOP WORK -MILLING MACHINE WORK_ The cutter arbor.
. 
2. Types of Shapers.—The ordinary types of shapers may be divided into column shapers and traveling-head shapers, the distinction being made largely on account of the style of the frame of the tool and the feed. In the column shaper the work is fed sidewise during the return stroke of the tool, while in the traveling-head shaper the head is fed sidewise during the return stroke of the tool. Column shapers may also be divided into two classes, crank-shapers and geared shapers, the division depending on the method of driving the tool. There are also several special types of shapers, or machines belonging to the shaper class, that will be considered after the work of the ordinary shaper has been discussed. 
COLUMN SHAPERS. 
CRANK-DRIVEN SHAPER. 
3. Construction of Shaper.-This class of shaper consists of a column A, Fig. 1, that supports the driving mechanism and the various stationary and movable parts of the machine ; a movable ram B that carries the cutting tool at one end ; and a movable table E to which the work is fastened. The ram B slides in flat bearings formed on top of the column ; at its front end it carries the shaper head D, which gives the down feed. This shaper head is so arranged that it can be swiveled around to make any angle with the top surface of the table. The ram is moved to and fro over the work by the driving mechanism within the column, which is operated by belting from a countershaft to the cone pul-ley J. The length of stroke and the position of the ram with reference to the work are adjustable. The shaper head D carries a tool block H similar to that of a planer. The table E is fastened by bolts to a saddle M, which is gibbed to the cross-rail I and can be moved along it either by hand 

§9 
SHAPER AND SLOTTER WORK. 47 
or by an automatic feed. The cross-rail can be raised or lowered by means of a screw on the vertical slide G, which forms part of the column, and can be clamped to it at any point. The table E usually has a removable vise F fitted to 

FIG. 1. 
it. To assist in supporting the table, a screw jack N is occasionally attached to the base of the machine. The amount of feed for each stroke of the ram can be adjusted by varying the position of a slide that can be locked by the handle L. 
4. Driving Mechanism.—The driving mechanism of the column shaper shown in Fig. 1 is illustrated by the two detailed sections, Fig. 2. A is the column or main frame, B is the ram that carries at the front end the swivel piece C. 

pg 144

pg 152 -MACHINE SHOP WORK  Duplex milling machine,,, the Becker Milling Machine.
Such machines are provided with the feed motions of the horizontal type, and also with a rotating table by which circular work can be done. A large amount of work formerly done in lathes 

Fig. 230. Vertical Milling Machine with Working Parts Shown in Ghost Courtesy of Becker Milling Machine Company, Hyde Park, Massachusetts 
is now being done in vertical spindle machines, as well as many pieces formerly machined on planers and shapers. Duplex Milling Machines. The duplex milling machine, Fig. 231, has both the horizontal and vertical spindles combined in one, which allows the spindle to be placed at any angle from horizontal to vertical, and combines all the good points of both machines. The 
■ 
 pg 153- 
head of the duplex miller can be moved out over the table so as greatly to increase the range of the machine; and this head is also provided with a drilling attachment whereby holes may be drilled at any angle. 

Fig. 231. Duplex Milling Machine Set for Cutting Spirals Courtesy of Van Norman Machine Tool Company, Springfield, Massachusetts 
MILLING OPERATIONS Classification. These may be classified in a manner similar to the cutters themselves, whose names will suggest the kind of work for which they are adapted. Plane Milling or Surface Milling. This is the machining of plain, flat, horizontal surfaces by means of cylindrical mills whose length is usually much greater than their diameters, the larger kinds being constructed with inserted blades or teeth. Side Milling or Face Milling. This operation is the machining of vertical surfaces, or surfaces at right angles to the axis of the milling cutter. 

  page 150-151  Machine Shop work-- Milling Machines 

 

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

   

 

          pg 152-153

 152 -MACHINE SHOP WORK  Duplex milling machine,,, the Becker Milling Machine.
Such machines are provided with the feed motions of the horizontal type, and also with a rotating table by which circular work can be done. A large amount of work formerly done in lathes 

Fig. 230. Vertical Milling Machine with Working Parts Shown in Ghost Courtesy of Becker Milling Machine Company, Hyde Park, Massachusetts 
is now being done in vertical spindle machines, as well as many pieces formerly machined on planers and shapers. Duplex Milling Machines. The duplex milling machine, Fig. 231, has both the horizontal and vertical spindles combined in one, which allows the spindle to be placed at any angle from horizontal to vertical, and combines all the good points of both machines. The 
■ 
 pg 153- 
head of the duplex miller can be moved out over the table so as greatly to increase the range of the machine; and this head is also provided with a drilling attachment whereby holes may be drilled at any angle. 

Fig. 231. Duplex Milling Machine Set for Cutting Spirals Courtesy of Van Norman Machine Tool Company, Springfield, Massachusetts 
MILLING OPERATIONS Classification. These may be classified in a manner similar to the cutters themselves, whose names will suggest the kind of work for which they are adapted. Plane Milling or Surface Milling. This is the machining of plain, flat, horizontal surfaces by means of cylindrical mills whose length is usually much greater than their diameters, the larger kinds being constructed with inserted blades or teeth. Side Milling or Face Milling. This operation is the machining of vertical surfaces, or surfaces at right angles to the axis of the milling cutter. 

page 154-155 Machine-Shop-Work Milling-Machines.
     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  164-165

Fig. 247. Side Milling Cutter on End Work TOOL-MAKING 
TABLE VIII Dimensions of Face Milling Cutters 
DIAMETER OF WIDTH OF TAPER OF HOLE CUTTER FACE (Brown & Sharpe Taper) (in.) (in.) (No.) c,* mloo C,INC9C,IN 10 12 4.1c 12 12 12 
way, and held in place on the arbor by a screw. The teeth should be made of tool steel and hardened, or of high-speed steel, if the cutter is to be subjected to rough usage. In either case, they can be fitted to the slots by grinding on a surface grinder, and held in place by taper bushings and screws, as explained under "Milling Cutters with Inserted Teeth". The construction of the body from the sectional view given in Fig. 249. represent diameter of cutter, width of face, and number of taper of the hole, respec-tively, while D represents the keyway. Table VIII gives the dimensions of face milling cutters of different diameters. After the taper hole has been bored and reamed, the body of the cutter should be placed on a taper mandrel fitting the hole, and the ends and cir-cumference finished to size. It is then put in the vise on the shaper or planer at the proper angle, and the spline slot cut to an equal depth at each end of the taper hole. The burrs having been removed, the cutter should be placed be milling machine, and the slots cut for the 
157 

Fig. 248. Face Milling Cutter 
can be readily understood The letters A, B, and C 

14-13-61 Fig. 249. Body of Face Mill 
tween teeth. 
the centers on the 

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 

 pg 168-169

pg-168 MACHINE SHOP WORK, Milling Gears 
Gears. The cutting of gears of all descriptions was formerly done on some type of milling machine, although now each type of gear may have its special and, in many cases, automatic machine. 

Fig. 243. Gear Cutter with Divided Head 
Forms of Cutters. The cutters for milling spur and bevel gears are of two types, producing both the cycloidal and the involute tooth. For each pitch, the cycloidal system requires twenty-four cutters, while eight cutters usually suffice for the involute system. These cutters are plainly marked with the style of tooth, pitch, and number of teeth for which they are suitable. Some cutters are also marked with the full depth of the tooth expressed in thousandths of an inch, Fig. 279. The gear blanks, having been very carefully turned as to outside diameter, are mounted on an arbor be-tween centers, and the cutter placed so that its central plane passes through, and is parallel to, the axis of the arbor. Clamp the saddle in this position; raise the table knee until the cutter, when rotating, just touches the outside of the blank. Using the table screw, move from under the cutter; using the graduated dial, raise the knee an amount equal to the whole depth of the gear tooth. With the exception of the indexing, the gear blank is now ready to be cut, Fig. 242. 

Fig. 244. Cutting a Bevel Gear 
MACHINE SHOP WORK 
169 
Use of Dividing Head. In order that the gear may be accurately and quickly set for cutting each tooth, a dividing head is used, which is shown in Fig. 243. The mandrel upon which the gear blank is mounted is held by the centers AA, and firmly dogged to the face-plate B. The index plate C is geared to the head spindle that carries 

Fig. 245. Hobbing Teeth in Worm Wheel Courtesy of Brown and Sharpe Manufacturing Company, Providence, Rhode Island the faceplate B; the index plate is provided with a number of holes. These holes are arranged in circles, each circle having a different number of holes, and these holes are accurately spaced at equal distances apart. The arm D carries a stem E, having a knurled head - at one end andaaPinn at the other. The pin is held in one of the holes. holes

 

>

   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.the last last Fly-Cutter Arbor 

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