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cessive. A rule-of-thumb measurement sometimes used is that the area of the air pipe shall equal six
times the area of the jet, but the foregoing method is much the safer one for computation. To facilitate
calculations, the following data are given:
At 2 pounds pressure, there will be required at the blower, roughly, about i000 cubic feet of free air per
minute per gallon of oil burned. Blast forges burn per day of ten hours approximately 0.15 gallon of oil
per square inch of horizontal area of firebox; open fires for hardening, 0.025 gallon; lead pots, oil
tempering, casehardening and annealing furnaces, 0.05 gallon. About io horsepower is required to
transmit i000 cubic feet of free air against 2 pounds pressure.
From the foregoing, a close estimate of the size of the required blower and the horsepower required to
drive it may be obtained. Included in this estimate must be a figure on the amount of air required to
blow the drop-hammer dies. The blowpipes required are one ii-inch pipe with flattened nozzle for each
small drop- and triphammer, and two of the same size for the larger drop-hammers. As the use of these
blowpipes is rather intermittent, this figure is generally in the nature of an off-hand estimate, based on
the judgment of the engineer.        E. H. M.
DROP-FORGING DIES. The art of drop forging has worked a great change in the product of the
blacksmith shop, both in regard to the quality and the quantity of the work produced. It has created a
new branch of the business, and has enabled forgings to be employed in thousands of cases where this
had formerly been impossible on account of the expense. Drop-forgings are made that weigh but a
fraction of an ounce, and others that weigh a hundred pounds or over. They are made from iron, steel,
copper, and bronze. Economy of manufacture, strength, interchangeability, and the general appearance
of the product, are all important factors in the production of drop-forgings. The dies by means of
which these forgings are made constitute an important factor in the process, and the making of these
dies is, practically speaking, a trade by itself.
Classes of Drop-forging Dies. — Drop-forging dies, like dies for the punch-press, are of several
different types. Perhaps the most simple form of drop-forging die would be a pair of dies for producing
a simple round forging, as, for instance, a gear blank. These dies would require a central impression
turned in each of the dies of the pair. Before using the dies, a square plate of steel is worked under the
hammer, drawing out a short shank at the side, and "knocking down" the corners. This roughly shaped
block of steel is held by the shank and placed between the dies and thus brought to shape. The most
common form of drop-forging die, however, is the one in which there is a central impression to shape
the forging, and a side impression, called the "edger," "break-down" or "side-cut," that helps to
properly distribute the hot steel. To make clear the use of these two sets of impressions, a drop-forging
die of this description may be likened to a drawing of the finished forging, in which the outline of the
central impression would resemble the plan view of the forging, and the two halves of the edger would
correspond to the side elevation of the forging. The edger is always on the right-hand side of the die,
and the steel bar is struck first in the breakdown, edgewise, and then turned and struck flat in the
impression, alternating in this manner until the forging is "full."
There are also dies that, in addition to the central impression and the edger, are made with an anvil or
"fuller," as it is sometimes termed. The anvil is formed in the dies at the left-hand side, and is used to
draw out the stock previous to striking it in the edger or in the impression itself. Dies with anvils are
necessary in making forgings in which there is a considerable displacement of the stock. A double-ended
wrench, which is thin in some places and very much thicker and wider in other places, may be
mentioned as an example. The anvil consists of two flat-faced parts of the die, the faces of which, called
"fullers," come just near enough together to flatten the stock to such dimensions that, when finished in
the central impression, very little stock will be left to be squeezed out as the fin. After the stock has
been thus drawn out to roughly fit the impression, the forging is shaped in the usual way by means of
the edger and the die impressions. A considerable number of large drop-forging dies require anvils. In
making the dies for difficult forgings, there are often other special features

Figs. x and 2. Typical Drop-forging Dies
incorporated in the dies, which will be more fully described later.
Typical Die Construction. — Fig. i shows the lower half of a set of dies with a break-down A, an anvil
B, and the die impression C. The sprue is shown at D, the gate at E, the flash at F, and the shank at G.
The excess metal around a forging that has just been completed in the dies is called the "fin," and is
removed in a separate operation, which may be done either hot or cold. If the forgings are to be cold-
trimmed, as is the case with most small forgings, the dies are
than two impressions are cut in the same set of dies, but, if the piece is small and the number of
pieces to be forged great, it is often advisable to make the set of dies with two or more finishing
impressions in addition to the forming impression. If this is done, the die has a longer life, because,
after one of-the finishing impressions gives out by spreading or "checking," there is still a good
finishing impression left.
Trimming Dies. — In addition to these different styles of drop-forging dies, the dies for trimming
the fin from the forging must be taken into consideration. As already indicated, trimming dies are of
two classes: (i) Those for trimming the forging while it is hot, and (2) those for trimming the forging
after it is cold. The making of drop-forging dies for forgings of other metals than steel or iron
involves the use of special methods. This phase of the subject will be described later.
Information Required by the Die-sinker. — Before the die-sinker begins making the die, he should
be given certain information about the work he is to do, in order to make a set of dies that will give
satisfactory results. As a general rule, he is furnished with either a drawing or a model of the
finished part, or with a sample forging. He must know what finishing operations the forging is to
pass through, so as to allow enough stock for machining, and he must know of what metal the piece
is to be made, so as to cut the dies large enough to allow for the shrinkage of the metal. With this
information supplied he must decide upon a number of other points that are largely a matter of
judgment on his part — points that have to do with the successful working of the dies. i. He must
decide whether or not to make the set of dies with a forming impression in addition to the finishing
impression. 2. The way in which to "face" the impression on the die-block so as to be able to use
the best form of edger. 3. Whether or not to include an anvil in the dies. 4. The type of hammer or
hammers the dies will be used in, so that the dies are made in blocks of the proper size. In making
the trimming dies, he must also decide whether or not to trim the forging hot or cold. With these
points decided, he is prepared to start the making of the dies.
Steel for Drop-forging Dies. — High-grade open-hearth steel is the material from which nine-tenths
of all drop-forging dies are made; a o.6o per cent carbon steel is used for most of the dies. In some
cases, however, steel as low as 0.40 per cent carbon and as high as o.85 per cent carbon is used, but
few shops use anything but 0.60 per cent carbon steel for the general run of work. If a low-carbon
steel is used, a special hardening treatment is required, which outweighs any saving in the price of
the steel. The high-carbon steels make good dies, but except in special cases, there is no necessity
for using so high-priced a steel. The average o.6o per cent carbon steel die, if properly hardened,
should last for from 15,000 to 40,000 forgings, and sometimes as many as 70,000 forgings are made
from one set of dies. Steel castings are not suitable for drop-forging dies, because flaws and blow-
holes are likely to develop in the dies. In making dies for large forgings, it is often considered
advisable to use o.8o per cent carbon steel for the dies, and not to harden them. This obviates the
danger of "checking" or cracking in hardening, and the steel, unhardened, is hard enough to resist the
tendency to stretch.
In Fig. 2 is shown, in section, a pair of drop-forgingdies for forging automobile hubs. Dies of this
design should be made of high-carbon steel and left soft on account of the projecting ring in the
bottom of the impression which would be likely to break off if the die were hardened. A steel fairly
high in carbon should always be employed for dies that are to be used for making forgings from tool
steel or other hard steel. When making forgings for very thin parts that cool quickly while being
forged, it is preferable to use tool steel for the dies, in order that they may be hardened to a depth
sufficient to withstand the tendency of the dies to "dish." A drop-forging die or any die used in the
drop-hammer, is said to be "dished" when the force of the blows it receives causes the central part
of the face to sink beneath the level of the remainder of the face. This condition results in forgings or
stampings that are too thick in their central parts. Dishing is usually traceable to a low grade of steel
or to improper hardening.
Preparation of the Stock. — The best method of preparing the die-blocks is to plane the stock in
lengths of from six to eight feet, after which it may be cut to any lengths required by the sizes and
shapes of the forgings for which the dies are being made. Occasionally a pair of die-blocks must be
planed for a special job, but it is quicker and cheaper to plane them in lengths when the work
warrants it, although many shops do not take advantage of this. The steel may be obtained from the
mills in ordinary sections suitable for dies 6 or 8 inches in height, which are the sizes mostly used.
At the time of planing, the dies are "shanked" with the proper bevel and height of shank, to agree
with the system in vogue in the shop where the dies are to be used.
The die-blocks are planed on the front and left-hand sides for a distance of two inches, or a little
less, from the face. These two cuts are merely "skin chips," and are perfectly square with each other
and with the shank of the die; their purpose is to furnish faces from which the impressions may be
laid out by means of a combination square and scribers. The reason for using the left side is because
the edger is always to the right, and, in cutting away for this part of the die, the lay-out face would
be destroyed. This would make it impossible to work from that side afterward, in case it should be
necessary to make changes in the impression. On the left side the anvil is formed; this interferes but
little with the working face that has been planed, because the anvil occupies but little space, at least
as regards depth. In planing these working faces, care must be taken to have the faces perfectly
parallel with the shanks of the dies; otherwise the two halves of the forging will appear to be
twisted with relation to each other, and, to correct the error, it will be necessary to "shim" the dies
— a practice that should be permitted only as a last resort.
There are various precautions taken to prevent blunders in the setting up of the dies. The forger
usually lines up the dies by matching the sides of the die-blocks. On dies the matching faces of
which have been cut away, the die-sinker usually cuts a deep "nick" from one die to the other, while
they are in ali.;nment. The shank of the upper die-block is milled with a "half-hole" to fit the
familiar "dutchman" in the hammer of the drop press.
Laying out the Dies. — The laying out of drop-forging dies is totally different from that of blanking
dies, this being due principally to the different allowances that
must be made for shrinkage, draft, and finish. The allowance for shrinkage is an important one. In
order to properly understand the considerations to be taken into account, it is necessary to
understand the trimming methods employed for removing the fin. Small forgings are invariably
completed, and the fin trimmed off after they are cold; such forgings are said to be cold-trimmed.
Larger forgings are trimmed hot and then struck once or twice in order to finish and straighten them,
as it is probable that the trimming has somewhat distorted them. At the time of the last blow, the
forging has cooled to a low red heat. In making dies for small cold-trimmed steel forgings, the proper
allowance for shrinkage is A inch to the foot or 0.015 inch to the inch. Such forgings are completed
at a bright red heat, and the rate of shrinkage is great.
In making dies for hot-trimmed steel forgings, which are of medium and large size, the proper
allowance for shrinkage is 8 inch to the foot or o.oio inch to the inch. Hot-trimmed forgings,
receiving the finishing blow while relatively cold, shrink a smaller amount than forgings that are cold-
trimmed. These proportions hold true for all dimensions of the die impression, whether they be
Fig. 3. Templet and Forging for Fig. 4. Ball Vise used in Hold-which it is used        ing Dies for Hand
no finish is required on the forging, in which case there would be no allowance. Usually, however,
there are bosses to be faced off or other places that require machining, and in such cases the forging
is left J1 inch oversize at these points.
Scribing the Outline. — In laying out the dies, the first step is to copper the faces of both the upper
and lower die, after which center-lines should be scribed from the two matching sides of the die-
blocks. If the forging is irregular in outline, it is advisable to make a templet. Not only will the
templet be useful in laying out the two impressions, but, if the forging is to be hot-trimmed, the
templet can be used in laying out the trimming die and punch. The use of a templet insures that the
two dies will match perfectly, for after laying out the lower die, the templet is simply reversed and
used for the upper die. The templet should be made of thin sheet metal, and, if brass or zinc is used,
it may be sawed out with a band or scroll saw and then filed to the line in the usual way. Fig. 3
shows at A a templet for a bevel-gear forging, with the various allowances made, ready to be used in
laying out the impression; B is the finished gear blank. First the outline of the finished forging is laid
out, then the draft allowance is added, and, at those points that must be machined, allowance is
made on the templet for this purpose. In laying out the set of lines for the shrinkage allowance, a
shrink-rule is used, either a 8 inch to the foot or a A inch to the foot, as the case may require.
Frequently, the outline of the forging at the parting line is simple and regular, as, for instance, in the
case of an eye-bolt forging. In the case of such a simple shape, there is no necessity for a face
templet, as the outline may be laid out from the two matching sides of the dies by means of a square
and dividers. In order that the outlines of the impressions on the two blocks may come in perfect
alignment, two and sometimes three combination squares are used in locating the templet on the
blanks, in case a templet is used. The templet is placed in its proper position on the face of one of
the die-blocks, and a combination square is set from each of the matching sides to the edge of the
templet. With the templet against the ends of the square blades, the outline is scribed; then, without
changing the blades of the squares, they are placed in corresponding positions on the other die-
block, thus locating the templet (now reversed), and the outline is scribed on this die. The
combination square also affords a good way for transferring lines from one die to the other. After
the outlines of the two impressions are scribed on the faces of the die-blocks, they should be either
lightly prick-punched at intervals along the lines, or they should be traced with a small, sharp chisel,
using the chisel after the manner of a punch, and moving it after each tap of the hammer so as to
obtain a clear,-deep, continuous line.
In planning the lay-out of a drop-forging die, there are several points that must not be overlooked.
The heaviest end of the forging should always be at the front of the die-block, as illustrated in Fig. i.
This makes the forging easier to handle while being forged and still on the bar, and it also permits the
use of a liberal-sized sprue. In selecting a die-block and laying out the impression, there should be at
least i* inch left all around the impression from the outside edge of the block or from any part of the
die, such as the edger, anvil, or forming

depth, width, or length. In making dies for forging bronze or copper, the same principles apply, and
the rate of shrinkage for cold-trimmed forgings is A inch to the foot, and for hot-trimmed forgings 8
inch to the foot, or practically the same as for steel.
Draft Allowance. — It would be very convenient if it were possible to sink forging dies with sides
perfectly straight, the same as a die-casting mold, but in die-sinking this is impossible, as the forging
would stick in the die. To overcome this tendency, "draft" is employed
•        the same as in patternmaking. The amount of draft
• given a drop-forging die varies from 3 to io degrees. If the die is for a thin regular forging, like an
oval treadle plate, 3 degrees is ample, but, if the forging die is deep and has narrow ribs which are
apt to stick, at least 7 degrees is necessary. If the die is to be used for forging a piece that is ring-
shaped or has a ring in its make-up, the central plug that forms the interior of the ring will require a
draft of io degrees, because, as the forging
• cools while being worked, it tends to shrink together around the plug, and, if the draft is
insufficient, it will stick in the die. With the above exceptions, however, the majority of drop-
forging dies are cut with a 7-degree draft. For convenience: in laying out, it is well to re-
i,,. member that a 7-degree taper equals practically a 8-inch taper to the inch, and a io-degree taper,
*-inch to the inch.
Allowance for Finish. — By " the allowance for finish" is meant the additional metal that is "put
on" the forging at those places that are to be machined. Sometimes

impression. If the forging has a hub or other projection that extends some distance from the body
of the forging on one side, the upper or top die should contain this deeper impression. This is an
important point, as every die-sinker and drop-forger knows that it is easier to "shoot" the metal
up than down.
Sinking the Impression. — The work of sinking the impressions in the dies may be roughly
divided into two parts: i. The machine work. 2. The hand work. In the machine work, the lathe
and the vertical milling or die-sinking machine are the two principal machine tools used. Generally
speaking, if there are parts of the impression that can be cut out on the lathe, it is good practice to
do this work first, although there are exceptions to this rule which will be mentioned later. The
advantage of doing the lathe work first lies in the fact that a large amount of the stock is removed
quickly and uniformly, so that the die-sinker has a better chance to start the milling cutters.
The best method of holding the dies for the lathe work is by means of a special bolster, bolted to
the faceplate. The bolster is planed to take the shank of the die-block, which is held in place by a
key. This method has certain advantages over the practice of holding the die-block with set-
screws, in that the block may be more easily made to run true, and there is less danger of the die-
block working loose. Much time may be saved in the turning if the lathe is equipped with a
compound rest, as the draft may then be bored out by swinging the rest over the required number
of degrees. If the lathe work is other than very plain, it is necessary to make use of templets. In
turning out the impression for a bevel gear blank, for instance, the templet for the turning would
appear as shown at A in Fig. 3. A study of this templet will give a good idea of the allowances for
draft, shrinkage, and finish. The lines of the finished gear show a straight hub, that is, there is no
bevel on its sides. In cutting the impression, however, these lines must be given a draft of 7
degrees in order to prevent the forging from sticking in the dies. The top and bottom of this hub,
as well as the face where the teeth are to be cut, must be machined; therefore, A inch is added to
the templet at these places. The shrinkage allowance is taken care of by laying out the dimensions
of the templet with the e inch to the foot shrink-rule, as the forging will be trimmed hot.
The Die-sinking Machine. — The die-sinking machine is, by far, the most important asset of the
die-sinker's equipment. At the present time, most die-sinking shops are equipped with machines
of the Pratt & Whitney make — the No. 2 machine for the small and medium work and the No. 3
for the heavy work. These two machines will take care of any dies to be made, and in small shops,
where but one die-sinking machine is installed, the No. 2 size will be found sufficient, if the work
is not very large. The dies are held in the vise of the machine, the shank of the die-block furnishing
a good gripping surface. The cutters are held in a spring chuck, that, by substituting different
collets, will accommodate cutters made of stock from 4 to i inch in diameter. This chuck is made
in three pieces and consists of a shank which is recessed to take a split collet, and a sleeve which
has an internal taper bearing surface. As the sleeve is screwed onto the shank, the split collet is
compressed, drawing together upon the cutter without throwing it out of center. The sleeve is
tightened by means of a spanner wrench, and notrouble is experienced from the cutter slipping in
this style of chuck.
Cutters for Die-sinking. — The subject of cutters for die-sinking is a very important one, because
neither good nor fast work can be done with poor cutters. The very best of roughing cutters can
be made from "stub ends" of Novo drills, and nearly every die-sinker takes advantage of this fact.
These short drills are ground ball-pointed on the cutting end, given clearance, and the center
ground out. This kind of cutter is so easily and quickly made, and stands up so well in "hogging
out" the stock, that it does not pay to use any other kind. For finishing, the cutters are made with
three or more flutes, so as to obtain smooth surfaces. Finishing cutters must be provided in a large
variety of shapes to take care of the various forms in the dies being cut.
The die-sinker is guided in the milling by the lines laid out on the face of the die-block and by the
index on the pilot wheel of the die-sinking machine, the scribed lines giving the outline, and the
index of the pilot wheel taking care of the depth of the various parts of the impression. Except
when using special cutters, such as hub and forming cutters, no oil is used on the tools. The
speeds at which the cutters should work vary with the size and style used. If the cutter is small,
the speed may be much higher than would be used with a large cutter. Special forming cutters that
are sometimes as large as 3 inches in diameter must run very slow, and the use of lard oil is
All circular parts of the impression are not bored out in the lathe, and it is inadvisable to bore out
any parts under 3 inches in diameter, especially if they are deep. These small circular depressions
are best taken care of by special forming cutters or by the circular attachment on the die-sinking
machine. A great many forgings for machine parts have bosses in which must afterward be drilled
a central hole. It is not practical to forge the part with the hole, but it is a great help to "spot" the
forging, and thus obviate the necessity of using a jig for the following operation of drilling the
forgings. To produce the projection in the die for this " spot," a so-called "hub cutter" is used. On
account of being milled out at the center, and relieved, this cutter will leave a cone-shaped
projection in the bottom of the impression that will produce a deep countersink in the boss of the
It is essential that a large cutter should be correctly located in relation to the outline of the
impression before being fed into the die. In order to check its location, it is well to scribe, from the
same center, a circle one or two inches larger than the one that is used for obtaining the outline. On
this outer circle, four points, equi-distantly spaced, should be prick-punched. After lightly
entering the cutter, the outline should be tested with dividers from these four points.
The Circular Attachment. — The circular attachment on the die-sinking machine is a valuable
feature in milling the impressions. By its use much circular work may be done that would be
awkward to bore out in the lathe, and short arcs may be cut much quicker than in any other way.
When this is used, a straight-pointed rod is held in the chuck in place of a cutter. The machine
table is adjusted with two feed handles until the indicating marks, placed on the sides for this
purpose, are in line. The table is lowered and the die-block located in the vise so that the center
point of the arc to be milled is directly
under the indicator in the chuck. Thus located, the table may be moved off-center far enough to bring
the cutter to the part of the impression that is to be milled, and the line followed by using the feed
provided. The old method of cutting these curves, used when the die-sinking machines were not
equipped with circular attachments, was to loosen the check-nuts of the swivel vise, and, after
moving the die to the proper distance from the center, clamp a long steel bar to the vise, and rotate
the vise by hand.
General Requirements in Die-sinking. — Throughout all the machine work on the impressions, as
little stock should be left to be taken out by hand as is possible, for not only is hand work slower,
but its quality can never equal machine work that is properly done. To this end, finishing cutters
should be run over the last cut two or three times, so as to obtain the smoothest possible surfaces.
The heavy milling should be done with a roughing cutter, held in the chuck close to the cutting point.
If, after the finish milling, the surfaces are smooth and the line is "split," there will be little left to be
done by hand save the corners and possibly a few irregular shapes that cannot be milled. In the final
milling cut for finishing to correct depth, exact dimensions may be obtained by setting the cutter so
that it just touches the surface
Fig. 5. Die-sinker's Chipping Hammer
of the die, and then moving the index on the pilot wheel to 'zero and raising the table to the required
dimension, as indicated by the reading of the index.
Hand Operations. — The really difficult work of die-sinking is the hand work that is necessary in
order to finish the impression; this part of the work requires more patience and manual skill than the
machine operations connected with die-sinking. Some impressions are full of corners and irregular
places that must be chipped out and smoothed by hand, nearly every job having a number of such
places. These places must be chipped, scraped, riffled, and polished, and, in order to facilitate this
finishing, the die is held in a ball vise. This useful device, shown in Fig. 4, rests on a pad of leather,
which in shop practice is made by coiling up a short length of 2-inch belting, and riveting it at
intervals. By the use of the ball-vise, the die may be held at any desired angle or position, and will
remain where put with sufficient stability to resist any ordinary chipping or filing.
Chisels and Chipping. — Die-sinker's chisels should be made from a good quality of tool steel. The
stock should be hexagon or octagon, and forged out to the shapes best suited to the work. Two or
three dozen shapes and sizes of chisels are necessary for the different shaped places that must be
chipped out in the general run of work. The most useful shapes are the round and flat varieties. The
round variety embraces a great many different curves. The flat varieties should run from Zh to 2 inch
in width. After hardening, the chisels should be drawn to a light blue, this temper being the same as
that given the ordinary cape chisel, and which will befound a good ordinary temper. The die-sinker's
chipping hammer, Fig. 5, is flat-faced and double-ended, so that either end can be used. To assist the
die-sinker in chipping out parts of the impression that are to be of the same depth, depth gages are
used, and occasionally the micrometer depth gage will be found indispensable; but there are few jobs
that require such accuracy. Shrink rules are also used in laying out the die impressions.
In chipping out the stock from the corners and other places that cannot be milled, there are a few
general rules that should be followed. It is always advisable to chip down or away from the outline
of the impression, for by so doing there will be no danger of breaking out "chunks" at the ends of the
cuts. In using flat chisels, care should be taken to leave as little work for the corners to do as
possible, as the corners are the weakest parts of flat chisels. Oil should be used sparingly on the
cutting edges of all chisels. For convenience in picking out the different chisels, it is a good plan to
keep them, points up, in round cans or boxes. In all chipping, light cuts should be taken, frequently
trying the templets and depth gages, so as to be sure that too much stock is not removed.
Scraping. — The idea of the chipping is to remove as much stock as possible from parts of the
impression that cannot be milled or otherwise machined. It is impossible, however, to finish the die
by chipping alone; therefore, after the bulk of the steel is taken out by milling and chipping, the
impression must be smoothed by scraping and riffling. Scrapers are of several different types.
Nearly every mechanic is familiar with the three-cornered and half-round scrapers, and both of these
tools are used at times in scraping out a die; but the most useful kinds of scrapers are those made of
square and half-round straight sections. These scrapers are short, made to cut on the end only, and
"pare" out the stock very quickly. These tools are fitted into short, round handles that fit the hand
snugly. After grinding and stoning the edge of the scraper, the corners are slightly stoned off so that
there will be no tendency to "dig in." By the use of the scrapers, the high points left by the chipping
operation are reduced, and the surface of the impression smoothed. Scraping is not intended to
remove much of the stock, but is more of a finishing operation. By scraping alternately in different
directions, the impression is kept free from grooves and ridges. Should there be any chatter marks
left by the milling operation, they may be taken out by scraping.
Riffling. — As soon as the die impression has been finished as regards dimensions with the scrapers,
the surface may be carefully smoothed by riffling. The rifflers, or small bent files, may be obtained in
a large variety of shapes, sizes, and cuts. The riffler is held lightly in the hand and is worked back
and forth over the surface to be smoothed. In other words, it is filing on a small scale. The most
comp on form is the "spoon" riffler, which comes in many different grades of curves, its name
describing its shape perfectly. By turning the riffler while using, many different kinds of curves may
be obtained, so that there are few spots in a die that cannot be reached with a spoon riffler. Another
useful type is the "flat" riffler, which is made in different shapes and widths to take care of the flat
surfaces and panels in the impressions. Other styles are the "hook" riffler, the "knife" riffler, and the
" round-taper" riffler. As with scraping, the rifflers must be worked over the surface

TYPING        DROP-FORGING DIES        489
with ever-changing directions to prevent the formation of grooves and ridges.
Polishing. — As a final finish to the impression, emery cloth, wrapped around a file or a piece of
wood, should be applied to every part of the impression, until the surface is perfectly smooth and
free from imperfections, using first the coarse and then the fine emery cloth. Often the shape of the
impression is such that it can best be polished with emery and oil used on the end of a stick of
wood. The emery will imbed itself in the wood the same as in a lap. The reason for this finish is to
get a good surface on the forging, and to assist the forging to come easily from the die while being
Types and Typing. — There are often irregular bosses or ends in a drop-forging die that cannot be
finished on the die-sinking machine, and that are particularly difficult to chip out, scrape, and riffle
to a finish. Usually these places are deep and narrow, and, generally, there are two of these
awkward places to cut out, one in each of the two dies. It is customary to take care of such places
in dies by means of typing. A "type" is a punch or small block of steel the end of which is shaped
exactly like that part of the forging that is difficult to cut. in the die. Types are hardened and drawn
to a purple temper. The part of the die that is to be typed is milled and chipped out to as near the
outline and depth as is considered safe. The face of the type is then rubbed lightly with Prussian
blue, placed in the impression, and, with a piece of copper or brass on its top, the type is struck
hard into the impression with a hammer. This operation leaves the high places with a blue facing.
These high places are next chipped away, care being taken not to go too deep, and the process is
repeated. If properly done, the typed part of the impression will gradually assume the shape of
the type and, by striking in the type a number of times, the impressions will take on the smooth
finish of the type and be ready for riffling. If the part of the impression to be typed is cylindrical,
the type may be turned up in the lathe; but if not, it must be milled and filed to shape.
In making types for shaping the impressions in dies for forgings the ends or hubs of which are
shaped similar to the forging shown in Fig. 6, the following rule should be observed: Shape the
sides of the type with a curve, the radius of which is equal to twice the diameter of the hub. This
rule insures the proper amount of draft on the impressions, and, as this form is commonly used on
bosses, at the ends of rocker arms, levers, etc., the application of the rule is frequent. In typing,
however, an exception to this rule is met with. Assume that a die is to be made for the forging
shown in Fig. 7. The impression would consist essentially of a ring with four projecting bosses
that must be typed. If the ring were turned first, difficulty would be experienced in typing the four
bosses, as the type would have a tendency to slide into the ring at every blow. In such a case, it is
better to mill out and type the bosses before doing the lathe work, in order to save time and trouble
in the typing.
Lettering. — When the forging must show lettering, the dies are usually stamped at the bottom of
the impression with the desired letters. This produces raised lettering on the 'forgings. The stamps
used are not the usual sharp-line stamps in common use in the machine shop, but are made deep
and with a flat face, so as to give body to the letters on the forging. In putting inthe lettering, care
must be used in the spacing, because, if too closely spaced, there is danger of the stock between
the letters breaking out. To space a word properly, the central letter of the word should be
stamped lightly in the center of the space to be lettered, and from this central letter the rest of the
word is added on either side. If the letters are extra large in size, it is advisable to mill or chip out
the letters after they have been lightly stamped in the die, after which they may be put in to the
full depth without a large displacement of the steel.
Gate and Sprue. — In nearly every case, a drop-forging is made complete while still a part of the
bar from which it is started and afterwards severed. To hold the forging while being worked, a
sprue must be provided. The sprue is the connecting link between the bar of rough steel and the
forging. To form the sprue, a channel is cut from the front end of the impression to the edge of the
die-block. The size of the sprue should be governed by the weight of the forging, and in all cases it
should be no heavier than is necessary to support the forging while being worked and trimmed.
The gate is an opening in the front of the die to receive the bar stock, and
Figs. 6 and 7. Examples of Drop-forgings
is made large enough to admit the bar without forging or crushing it at all.
Taking Lead Proofs or Impressions. — For the purpose of ascertaining how the forging will look
when it comes from the dies, as well as to check up the shrinkage allowances and to find any
defective places in the impression, it is customary to take a lead proof from the finishing
impressions of the upper and lower dies after they have been completed. Frequently the machinist
would like to be able to use a "putting-on" tool in his work, especially after he has read his
micrometers; with the die-sinker it is very easy to put on stock if the forging needs it, by simply
making the dies a little larger at the desired point. A lead will show up any places on the forging
that may need more stock; also, by weighing the lead, an idea of the weight of the finished forging
may be obtained. Roughly speaking, the finished forging will weigh two-thirds as much as the lead
proof. The shrinkage of lead is practically the same as that of steel, so that the finished forging will
measure very nearly the same as the lead. In the case of dies for eye-bolts, etc., this rule must be
disregarded, because the plugs in such dies that form the central openings will hold the lead from
shrinking naturally, whereas the forging shrinks most after it has been taken from the dies.
In taking the lead proof, or "lead," the impressions in both the upper and the lower dies are cleaned
out, dusted with powdered chalk, and the dies stood on end, after which the dies are clamped
together with a large C-clamp, care being taken to have the matching sides perfectly in line with
each other. The lead is now heated, care being taken not to burn it, and is poured slowly and