US1810537A - Drop hammer - Google Patents

Description

June 16, 1931.

J. N. SCISM DROP'HAMMER I;

3 Sheets-Sheet 1 Original Filed Oct. 5, 1923 INVENTOR. Jo/M Nz'ver .S'cz'sm A TTORNE Y.

J. N. SCISM DROP HAMMER June 16, 1931.

3 Sheets-Sheet 2 Original Filed Oct. 5, 1923 INVENTOR.

Join Nl'ver Scz'sm A TTORNE Y.

June 16, 1 3 J. YN.SCISM 1,810,537

'vaor HAMMER Original FiledOct- 5, 1923 s Sheets-Sheet '3 Fly. /6

IN VENTOR Join JVz've r Scism BY V,

ATTORNEY Patented June 1 6, 1931 JOHN mvERsoIsM, or HARTFORD, ,oonn'acriou'r tenor HAMMER Application filed October 5, 1923, Serial No. 666,730. Renewed l'l'ovember 20, 1930.

Heretofore board drop hammers haveseldom been made above the catalog rating to of 3000 pounds capacity. One objection has been that such larger hammers would require unusually strong buildings to withstand the heavy intermittent pull of the belts when,

7 driving the hammer in the usual Way from a 15 shaft and pulleys attached to parts of the building.

In gearing the front and rear rolls in the customary manner, as shown in my aforesaid application, I have found that when the 530 front roll is thrown out of engagement with the board,'the driving gears of the rolls are moved out of proper mesh. This has a de structive effect upon the gear teeth. Furthermore, such gearing seems to require 2. special gear teeth which are not as strong as 7 standard teeth. v

The object of the present invention is to overcome the previously mentioned objections and to further provide an improved drop hammer with an electric motor driving mechanism attached to the top portions of the hammer frame which has sensitive cushion- 'ing means to absorb the shocks and vibrations from the'hammer before they can react on the motor with any injurious effect.

Another object is to provide means where by two hammers can be driven by one motor drivin mechanism, with a saving in cost of D equlpment.

A further object is to provide means wherebytwo front friction rolls of a four roll hammer can be controlled as easily as one pair and thrown in and out of engagement with the board.

Other objects will appear later in the description.

In the drawings accompanying and forming a part of the present specification, I have shown in detail several embodiments of the invention, which 'to enable those skilledin the art to practice the same will be set forth fully in the following description.

Fig. 1 is a right side elevation of the upper portions of a hammer with the driving mechanism partly in vertical section, the control mechanism for the operation of the rolls not'being shown. v j

Fig. 2-is aleft side elevationof the ma-' chine showing the means for engaging and j disengaging the rolls with the board. on

Fig. 3 is a fragmentary View, showing in side elevation the rolls and their associated gears. r

Fig. 4 is a plan View of Fig. 5, showing one form of lever arrangement for controlling the eccentrics and rolls of the'machine.

' Fig. 5 is a side elevation of Fig. 4.

Fig. 6 is a view in side elevation, showing one form of a portion of the frame and cushioning means for the driving mechanism. 7

I Fig. 7 is a view of the left-handeccentric lever, projected at an angle from Fig. 2.

Fig. 8 is a bottom plan View, showing a detail of one link of the mechanism.

Fig. .9 is a fragmentary plan View of the machine, with part of the driving mechanism omitted.

Fig. 10 is of Fig/12.

Fig. 11 is a fragmentary View, in rear so elevatiomshowing portions of universal joints and one of the intermediate shafts for driving a second hammer.

Fig. .12 is a fragmentary View, in rear v elevation indicating a second hammer and 11 a lower intermediateshaft and other. cona plan view, showing adetail nections.

Fig.13isa side elevation (partly in vertical section) of Fig. 14.

Fig.1i is an end view of Fig. 13. to Fig. 15 is a, rear elevation, showing the upper portion of a drop hammer with its driving mechanism; p Fig.16 is a portion of'a'left side elevation of the machine frame siniilar'toFig. 2 with some'details omitted. i 17 is a. view'of, the left handeccentric lever projected at an angle from Fig.

16 and is the same as Fig. 7 except that the gear 200 is geared to it. Y Y

I have shown a drop hammer, the general construction of which, other than the improvements herein described, is well known, and no attempt is made therefore to illustrate fully and describe features of the hammer which are in common practice.

For the reasons stated I have shown various embodiments of a drop hammer and its driving mechanism positioned at the top of the machine.

IVhile the cushioning means for the driving mechanism and various parts of the driving mechanism are very similar to the construction shown and described in my former applications, Serial No. 636,463 and Serial No. 651,602, it is desirable at times to place the driving mechanism' at the top of the machine. This necessitates several departures from the structures shown in my former applications.

I prefer to use rubber blocks for cushions, and the rubber of which the cushions are made is of about the same quality as in generally used for automobile truck tires. Various depressions or holes may be formed in the rubber to get the best cushioned effect. These rubber cushions are to be made in steel moulds so that they will be of a uniform size and cure, and can be replaced more easily. I may also employ helical springs or elliptical springs or other forms of springs to serve in combination with rubber blocks or in place of them.

It will be noted that instead of one pair of rolls which are commonly used on drop hammers, I employ two pairs for extra heavy work. While I do not claim any invention in merely adding an extra pair of rolls, I believethat my arrangement of gears for driving four rolls, and the means for operating the eccentrics to control the engagement of the four rolls with theboard have unusual advantages over the prior art and are important features of'this invention.

It is obvious that the motor driving mechanism including its vertical shaft and worm can be applied to a two roll hammer, as well as to a four roll hammer. In that case the worm will drive one worm gear instead of two, as shown.

The worm and worm gears shown are intended to represent the most common typea self-locking typewhich is used for light and medium work. In extremely heavy work and for hammers driven in pairs I prefer to use what is quite commonly known as the Hindley worm and gear, which type of gearing has a much greater tooth area in contact, to take heavy loads without cutting.

It will be noted that the driving mecha nism does not show a fly wheel. If a motor of sufiiciently high rating is used no fly wheel will be necessary, but if a motor of less horse power is used a fly wheel can be used on that purpose.

In some places I'have shown shafts, on which are fitted number of parts; the shafts are shown with cotter pins in their ends to hold the parts together, and in some cases the shafts are held in place by a drive fit, or by nuts, or set screws. In all such parts I do not wish to confine myself exactly to such details, as it is obvious that various combinations of commonly known lock washers and their equivalents may be used to keep the parts from coming loose.

Referring first to Fig. 1, I have shown an upper portion of a drop hammer, comprising a head at 2, and a pair 3 of uprights on which the head is supported. On head 2 are bosses at and 5 and 6; bosses 1 and 6 provide bearings for shafts 7 and 8 respectively. Near the ends of shaft 8 and keyed to it are levers 9 and 11. (Figs. 9 and 15). Levers 9 and 11 are also secured to shaft 8 by set screws 10. In the ends of levers 9 and 11, pins 1&- movably secure forked members 12 and 13, respectively. In the lower ends of members 12 and 13, pins 16 movably secure one end of links 15. The opposite end of links 15 are pivoted on the ends of shaft 7 and tightly held by set screws 17. I may key links 15 to shaft 7 also to cause them to pivot in bosses 1 as one member that is, in the same manner that the members 8, 9 and 11 pivot. The levers 9 and 11 have fitted in their lower ends rubber blocks 18, as is best shown in Figs. 9 and 15, and these rubber blocks also rest against lugs 5. I can also use various forms of springs in place of these rubber blocks. In this manner the forked members 12 and 13 are always held in a vertical position and at the same time are free to move upward and downward, depending on how much the rubber blocks 18 will yield and spring back. The centers of shafts 7 and 8 and pins 14 and 16 are always in the intersecting points of planes forming a parallelogram or a rectangle. The forked members 12 and 13 are tied together at their top ends by beams 19 and 20. The ends of said beams are bolted to members 12 and 13 at 21, 22, 23 and 2a, in Figs. 1 and 9, the ends of the bolts being upset. To brace members 12 and 13 still more tie rods, 25 and 26, are secured to lugs projecting from members 12 and 13 at 27, 28, 29 and 30. A platform 31 is suspended from beams 19 and20, by means ofro- ds 32, 33 and 34: and 35. On the ends of these rods are nuts 36 and 37, and between these nuts and the said beams are thick, round, rubber washers, serving as cushions at 38, and also thin steel washers at 39 of same diameter, see id igs. 1 and 9. In a similar manner rubber and steel washers are clamped by nuts 12 to platform 31 at the lower ends of the same rods at %O and 11, respectively. I also show wood spacer the motor shaft.

V shafts to the other.

blocks 1-3 held on the same rods by cotter pins. It is obvious that helical sorings may be used in place of the rubbers 38 if desired.

. The motor 44- is bolted to platform 31 by bolts 15,- in Fig. 1, the holes for the same being shown in the platform 31 at 46 in Fig. 9, said platform being broken away in its middle toshow a gear box which is on the hammer. The platform 31 has a gear bracket 17 bolted to it at 4:8. This bracket provides a hearing at 49 forshaft 50 and also a bearing for. same shaft at 51, 1, which is the end portion of an arm 52, in Fig. 15. The shaft 50 is broken off, in Fig. Between bearings 49 and 51 and'on shaft50 is a bevel gear 53. A washer 55 is fitted between gear 53 and bearing 4.9 to

facilitate assembling and to admit of re. placement of worn parts. is driven by bevel pinion 56, shown keyed to At the extreme lower end of shaft 50 is a fiexible'coupling 57, the up per half of which is keyed to 50at 58, and is also held by set screwsat 59, in Fig. 1. The

lower halfof flexible coupling 57 extends along neck 67 which is keyed at 61 to a shaft 62 having a slip fit in the coupling, the end of shaft 62 being shown at 63 to provide ample clearance from upper shaft50 when the latter, and other parts on the platform, 2

spring up anddown from the yielding'motions of the cushions, which motions are, of course, caused by shocks of the hammers. On the'u'pper end of shaft'oO, Fig. 1, is fitted a collar 64 which istightly held by a set screw 65. The platform 31 and gear bracket 47 have each around hole 66 to provide clearance for coupling 57. An enlarged detail of coupling 57 is shown in Figs. 13 and 14;; This type of flexible coupling is well known. It iscommonly used for coupling electrical inachinery or for coupling electrical to other machinery where two shafts, not in exaotalignment, are to be connected. They supply the flexibility necessary to prevent injurious stresses and shocks from being transmitted from one of said I may also use various other flexible couplings now in common use suchas two disks made of strongfabric and rubber,-and bolted together between two steel flanged coupling members. The bolts are generally six, in number and each alter nate bolt is tightly fitted in the flangeof one of the steel members, and has considerable play in the other.

Another type commonly used comprises.

, two endless belts laced alternately over prongs on'a spider form of each half of the coupling. 1

In Figs. 13 and 14, I show six bolts 69.

7 Each alternate bolt is tightly fitted in one flangeof the coupling, but has considerable play in the'other, and washers "Z0 and the fiat leather links 71 are secured to the bolts,

The bevel gear 53 so that the members 67 and 68 are flexibly interconnected. Therefore the shocks and vibrations on thecoupling portion 67, transmitted from the hammer through shaft 62, Fig. 1, are considerably absorbed by the leather links 71' before they can reach the coupling member 68 which is rigidly secured to the shaft 50 of the driving mechanism. The greater shocks on the said coupling come'from a vertical direction as the hammer strikes. Besides the. shock absorbingleather links, I provide aslip fit for the coupling member 67 on shaft 62 which fitallows a free up and down movement of the coupling on shaft 62. It will be noted that the platform 31 hangs on rods 32, 33, 34 and 35. Said rods are made as small as possible, and yet are strong enough to It is obvious that if desired more rubber washers can beused at 38 anddO for the four rods to get a better cushioning effect.-

upper part of the worm 72; The worm is somewhat exaggerated in size. The lower part of the worm 73 is solidly united with worm 72 by a short shaft 7 1, in Fig. 1, which ing of gear box at 80, half of the bearing being in the gearbox 78: and half in gear box cap 81. A similar bearing is provided'at 82 for shaft 62 to run in, the said gear box and cap being bolted together on line 83, of Figs. 9' and 15, a flange 87 being provided on both 78 and '81. A gasketnot shown may be used for a tight joint, as the box should be full of thick grease to lubricate the gears. Thrust washers 86 are provided on shaft 62, Fig. 1, to take the thrust ofthe worm'at the top of thegear box. .Also a-washer 89 is fitted between'the lower part of worm 73and a boss onthe inner wall of the gear box in Fig. 1. The inn'e v'wall of the gear box is shown at 88, in Figs. 1 and 9 and 15. -The inner wall of gear box cap 81 is shown at 90, Figs. Sand 15. In-the gear box bosses are provided at 91 for two rear. shafts 92and 93, and similar bosses 94 are formed in cap 81. Gear box 78 is dovetailed to head2 of the machine at 95, and when theshafts 92 and 93 are passed through said box, it is locked in place. Keyed on these two shafts are two worm gears 96which are both driven clockwiseby the worm, 72, -73.

In Fig. 1 the shaft 62 is integral with the I for adjusting these shafts.

Both gears 96 have a running fit between bosses 91 and 94.

The head 2 has two upwardly projecting portions at 97 and 98 on top of which are fitted caps 105 and, 106, which are bolted down by bolts 107 through lugs projecting from caps105 and 106. These provide bearings for shafts 92, 93, 99 and 100, which are shown keyed to rolls 101, 102, 103 and 104, respectively. The roll 101 and shaft 92 are broken to show front roll. The two rear shafts 92 and 93 are preferably running in.

stationary bearings, although I may, according to common practice, provide eccentrics The two front shafts 99 and 100 run in eccentrics for their bearings, the eccentrics also being free to turn in their bearings, as shown in Figs. 2, 9 and 15. The lower front shaft 99 has left hand eccentric 108 (Fig. 2) and right hand eccentric 110 (Fig. 1). The upper front shaft 100 is trunnio ed in eccentrics 109 and 111, which eccentrics are formed with short lever arms, such as the arm indicated in Fig. 2. At the ends of these levers, round necks 112 and 113 are provided, as seen in Figs. 9 and 2. These necks form bearings for a shaft 115 to turn on, which shaft is driven in the end of link 116, and between said necks. The eccentrics 108 and 110, Figs. 1 and 2, are similarly formed with lever arms 117 (see Fig. 7). Both eccentrics 108 and 110 are slotted, as shown at 118 in Figs. 7, 9 and 15. They also have lugs 119 and 120 2 and 7), 7 and 114, which meet at 121 15) and form bearings for a pin 122 which is driven in each to tie them together. In the slots 118 (Figs. 9 ant 15) are pinned the links 123, free to turn at 124, Figs. 2, 9 and 15. On one end of each link 123 a tight bearing 125 is formed for a shaft 126 which turns in links 127, Figs. 2 and 9. The upper ends of links 127 are tightly fitted to shaft 128 which turns in end of link 116. In the lower ends of links 127 is tightly fitted a shaft 129 which turns in the enlarged end of control bar 13 (Figs. 2 and 9) One of the important features of this invention is the rotation of the eccentrics on the upper and lower front shafts in opposite directions to provide a positive control for simultaneous engagement of two pair of rolls with an elevating board. Another advantage is that itprovides means whereby the driving gears for four rolls are maintained in proper mesh, although two 'of said gears are on moving shaft centers.

WVhen the control bar 130 is dropped, the eccentrics 109 and 111 are revolved clockwise, as shown in F ig. 2, because the links 1 7 will swing toward a vertical position or approximately in line with bar 130, and in dolng so the link 116 together with the upper eccentric arms must be pulled forward and at the same time links 123 must push rearward and revolve the eccentrics 1'08 and 110 counter clockwise. In this manner the rolls 103 and 104 are thrown into engagement with the board 131 at approximately the same time. I may add to this structure or vary the arrangement of the links. For instance I may add a thin spur gear by keying it or making a friction fit on eccentric 108 adj acent to 117 of Figs. 2 and 7, and when assembled the gear will be between 117 and surface 132, Figs. 9 and 15. This gear ma Y mesh with another spur gear of the same size, and number of teeth which may be keyed to 109, Figs. 2 and 9, andwhich may be be tween 114 and surface 132. I may use two gears in this manner having plenty of back lash so thateccentrics 108 and 109 will have a limited amount of independent rotation and besides this they will positively rotate together to engage the rolls 103 and 104 with board 131 at about the same time. It is also obvious that friction discs may be used instead of said spur gears. In that case the friction discs may be the same diameter, as the pitch diameter of said gears and one disc may roll on the other. Alternatively I may use similar gears just outside of the head 2 of the machine, mounted on eccentrics which are extended sufiiciently, and in that case I may mount one of the gears on an eccentric like a band brake with well known brake lining. In that case I may use standard gears in perfect mesh.

Two previously mentioned gears are shown in Figs. 16 and 17 at 200 and 201. A few of the teeth in each gear are shown, and the remaining circumferences shown by light dot and dash line to represent the outer diameters of teeth, pitch diameters and root diameters. The gears 200 and 201 are the same. The key 202 is smaller than the slot in the gear for clearance at 204. The gear 200 is preferably a tight friction fit on 108 and has a limited rotation for the key 202.

It is obvious that if desired such gears may also be applied when using a modified form of link motion, as I show in Figs. 4 and 5, the eccentrics 108' and 109 being the same, respectively, as 108 and 109 already described in Figs. 2, 7, 9 and 15. They (108, 109) are rotated in same directions for engaging the board. The link. 12.3 is the same as 123 of Figs. 2 and 9. Also various other parts are the same and I will, therefore, describe only those parts which are modified. The links 116 and 123' are hinged to turn on shaft 126. Also rod 130' has drive fit on 12, the link 116 being slotted at 133 to fit enlarged head of 130?. When 130 is allowed to drop, as is customary in the operation of hammers, the links 116 are pulled over, whereby 109 is rotated clockwise and link 123 is pushed to rotate 108 counter clockwise. In case 116 should move with less resistance and far enough to engage the 2 to give a bearing for gear 130.

roll controlled by 109 with the board, before 123 has rotated 108 far enough to engage its roll with said board, the engagement of the first roll with the board would give such slight friction as to be negligible in doing any work until the second named roll engages the board and vice versa. Therefore, the effective engagement of the rolls with the board actuated by 108 and 109 with sufli cient friction to elevate the board and its bearing hammer head must be practically at the same time. I

Referring again to Fig. 2, I show spur gears 134, 135, 136 and 137, respectively, keyed to shafts 92, 93, 99 and 100. The teeth and pitch diameter are represented by broken lines; the gears are also shown in Figs. 9 and 1.5, and diagrammatically in Fig. 3. The gears are held on by washers, nuts and cotter pins secured to ends of said shafts. in Figsf9 and 15, but for clearness they are left ofl? in Fig. 2. The ends of said'shafts are of reduced diameters for nuts, as shown in Fig. 2. In Figs. 9 and 15 a boss 138 projects from head Also gear 137 runs against the end of eccentric 109, said eccentrics 108 and 109 each have clearance key slots 139,.as shown in Fig. 9, for assembling purposes. In Fig. 15 is shown a bushing 140 with a head outside of head 2 for assembling purposes and for gear 134 to run against. Gear 136 runs against projecting end of eccentric 108, as shown in Fig. 15. Gear 134 drives gear 136, and similarly gear 134 drives gear 137, see Figs. 2, 3 and 15. In order to keep these gears in proper working mesh while front shafts 99 and 100 are moving withtheir eccentrics, and on which shafts the gears 136 and 137 are keyed, I have positioned the shafts 99 and 100 (best shown in Fig. 3) so that their centers rotate with said eccentrics in the arcs 141 and 142, respec tively. Accordingly, roll 99 in its extreme position 143 holds its roll 103 out of engagement with the board, and in position 144 causes engagement between the roll and board. The eccentrics are so'designed that their extreme positions 143 and 144 lie equidistant from and upon opposite sides of a line 145, which line passes through the center 146 of eccentric 108 and through the center of gear 135. And, further, when roll 103 is in the engaged position with said board, its center position 144 should then be approximately in a line 147 perpendicular to said board and passing through the center of the opposite roll 101. This is desired to the end that the board may be elevated without bending. It will readily be seen, therefore, that the centers 143 and 144 which are the approximate extreme positions occupied by gear 136 are equally distant from the center of gear 135 which drives it. It is, therefore, obvious that when the center of roll 103 travels from 143 to 144 through the are 141, its distance from thecenter of driving gear 135 is decreased only a very small amount. In actual practice it may amount to about one thirty second'part of an inch because the distance from 143 to 144 in practice need not'be more than about one-half or five-eighths inches. As these gears are of the involute form of teeth it is well known that such a small variation on center distances of the gears is considered practically a perfect mesh and will stand hard service.

In a similar manner the extreme positions of travel in the. are 142 for the center of roll 104 are at points 148 and 149 which are equally distant from line 150 passing through center 172 of gear 134 and center of eccentric 109. Therefore, the gears .134 and 137 are always inmesh, as wasshown and described for gears 135 and 136. I

Referring again to the cushioning means for this driving mechanism, I have shown in Fig. .6 a further embodiment of Fig. 1. A wood beam 19 represents a portion of a beam, similar to the beam 19 in Fig. 1. -And the numerals 13, 37', 29', 32, 39', 23, 36 also indicate parts similar to those denoted respectively by the numerals 13, 37,29, 32, 39, 23

and 36. This illustrates how flat steel springs 151 may be utilized. A block or washer 152 is usedasaspacer above and below beam 19, and they are bolted together with the other parts at 23. A rod 32 passes through both springs 151and beam 19, and holds them in place. The washer 152 is made of such thickness that the springs 151 may have ample space to yield toward the beam 19 and still have a little clearance so that in case springs 151 should break, the rod 32 could drop only a very short distance. this manner springs may be used with a very small factor of safety. .The lower spring 151 serves to prevent excessive rebound. I may also use a rubber washer (similar to the washers 38, Fig. 1) between 151 and 39 on the top side. This illustrates how springs may be used fora driving mechanism which is similar to what is shown in Fig. 1, and may be in all other respects the sam I may drive two hammers with one motor driving mechanism.

Referring again to Fig. 1, it will benoted that the gear bracket 47 has a hole 190, the hole 190 being-alsoshown in Fig. 15. This hole provides a bearing for a shaft which may project from the side of the bracket 47 to hold a flywheel. The shaft may be geared to the gear 53 with anotherpinion, similar to the pinion. 56, when necessary; it is a similar arrangement to what is shown in Fig. 4 of my application SerialNo. 651,602. A hammer of large capacity is quite. high, and there may notalways be room available for a flywheel on the shaft 50, and in that event it may be connected to the bracket 47 as described.

It is obvious that pneumatic rubber blocks L simultaneously and arcuately in opposite or hollow rubber blocks filled with air may be used in place of blocks 38 which are shown in Figs. 1, 9 and 15.

hat I claim is l. A drop hammer comprising aboard, a pair of upper rolls, a pair of lower rolls, the front upper roll and the rear lower roll being mutually geared and the lower front roll and the upper rear roll being mutually geared, and eccentrically mounted shafts connected with both of the front rolls and so arranged that the centers of the front rolls are movable directions to engage and disengage the board and to maintain proper engagement of the gear teeth.

2. A drop hammer comprising a board, a

air of lower rolls, a pair of upper rolls, the rolls of the two pairs being in direct vertical alignment, gears mutually connecting the front lower roll and the rear upper roll, gears mutually connecting the front upper roll and the rear lower roll, eccentrically mounted shafts connected with each of t 10 front rolls and arranged to move the centers of the front rolls simultaneously and arcuately to engage and disengage the board, a control bar, and links connecting the control bar with said eccentric shafts so arranged that a simple movement of the bar in one direction causes the links to rotate the shafts in opposite directions to move the centers of the rolls oppositely thereby separating the centers of the rolls whilemoving the rolls into engagement with the board.

3. In a drop hammer the combination of board, a pair of upper rolls, a pair of lower rolls, one roll of each pair being disposed on one side of the board and the other roll of the pair being disposed on the opposite side of the board, the upper roll on each side of the board being diagonally geared with the lower roll on the opposite side 0 the board.

4. In a drop hammer the combination of a board, a pair of upper rolls, a pair of lower rolls, one roll of each pair being disposed on one side of the board and the other roll of the pair being disposed on the opposite side of the board, the upper roll on each side of the board being diagonally geared with the lower roll on the other side thereof, and eccentrically mounted shafts connected with the two rolls on one side of the boardarranged when actuated to move the centers of the rolls arcuately in opposite directions, the arrangement being such that the line of movement of each of the roll centers crosses the diagonal line between its center and that of the roll to which it is geared.

5. In a drop hammer the combination of a board, a pair of upper rolls, a pair of lower rolls, one roll of each pair being disposed on one side of the board and the other roll of the pair on the opposite side of the board, the upper roll on each side of the board being diagonally geared with the lower roll on the opposite side of the board, a control bar, an arm pivotally connected with the control bar, and links pivotally connected with said arm and each connected with one of the rolls on the same side of the board so arranged as to substantially equalize the pressure eXertec by the rolls'on the board upon actuation of the control bar.

6. A drop hammer comprising a board, a pair of upper rolls, a pair of lower rolls, the front upper roll and the rear lower roll being mutually geared, eccentrically mounted shafts connected with both of the front rolls and so arranged that the centers of the front rolls are movable simultaneously and areaately in opposite directions to engage and disengage the board, a control bar, an arm pivotally connected with the control bar, and links pivotally connected with said arm and each connected with the eccentrically mounted shaft of one of the rolls on the same side of the board, said links being so arranged as to substantially equalize the pressure exerted by the rolls on the board upon actuation of the control bar.

7. A drop hammer comprising a board, a pair of upper rolls, a pair of lower rolls, the front upper roll and the rear lower roll being mutually geared, eccentrically mounted shafts connected with both of the front rolls and so arranged that the centers of the front rolls are movable simultaneously in opposite directions to engage and disengage the board, means for actuating said shafts, and gears interconnecting the mounting means of said shafts.

8. In a drop hammer the combination of a board, a pair of upper rolls, a pair of lower rolls, one roll of each pair being disposed on one side of the board and the other roll of the pair being disposed on the opposite side of the board, two eccentrically mounted shafts connected one with each of the two rolls which are disposed on the same side of the board arranged when actuated to move the centers of the rolls arcuately in opposite directions, common actuating means for said shafts, and gears interconnecting the mounting means of said shafts.

' In testimony whereof I aiiiX my signature.

JOHN NIVER SCISM.

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