US 2208843 A
Description (OCR text may contain errors)
Jilly 23, 1940. T. L. HEDGPETH 2,208,843
POWER DRIVEN TOOL Filed May 7, 1938 3 Sfieets-Sheet 1 Ziaflezaior Term Z. jfeaj vei @wkeM/M July 23, 1940. T. 1.. HEDGPETH POWER DRIVEN TOOL Filed May 7, 1938 s Sheets-Sheet 2 W 0 H z A by m July 23, 1940.
\POWER DRIVEN TOOL Filed May '7, 195a T. L. HEDGPETH '4 3 Sheets-Sheet 3 Patented July 23, 1940 r 2,208,843 POWER DRIVEN TOOL Theron L. Hedgpeth, Oak Park, Ill., assignor to Duro Metal Products Company, Chicago, 111., a corporation of Illinois Application May 7, 1938, Serial No. 206,616
This invention relates to power driven tools and particularly to power driven tools-such as scroll saws in which a flexible element, such as the saw, is positively actuated at oneen-d and is subjected to continuous bias at the other end.
Such tools are driven at very high speeds, in fact, at speeds which are almost vibratory in nature and the flexible members are subjected to undue strain and whip, particularly at the times l0 when the direction of movement is being reversed.
In accordance with the present invention I subject the flexible member, for example the saw blade, to spring tension at opposite ends sothat it is always maintained in a state of tension. I
applied at each end may be varied at will. Ordinary I find that the best operation is attained when the tension applied at opposite ends of the flexible member is approximately the same. I prefer to provide improved spring means which are subjected to very little change in tension as a result of the displacement to which they are subjected in the normal operation of the tool. The invention will readily be understood from the following description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings, in which:
Fig. 5 is a fragmentary sectional view, taken on the line 5-5 of Fig. .4, showing the pump I mechanism;
Fig. 6 is a fragmentary sectional plan view, taken on the line 6-6 of Fig. 3, showing the spring mechanism associated with the upper end of the scroll saw blade, and
Fig. '7 is a fragmentary sectional detail, taken on the line 1! of Fig. 4.
Referring to the drawings, the improved saw comprises a base on which is mounted a motor I2 with the aid of an adjustable bracket M. The base I0 carries a housing I6 within :which is provide simple means whereby the spring tension Figure 1 is a perspective view ofa scroll saw located the drive mechanism I8 whereby the saw blade is reciprocated up and down. On the housing I6 is carried the air pump 26, which is best seen in Fig. 5. The lower spindle assembly 22 is mounted in the housing l6 and the work table 24 is mounted on the housing l6 by means which will hereinafter be more fully described.
The saw comprises an overhanging arm 26 which is secured to the base ill by bolts 28. This arm is preferably hollow and comprises an upright portion 36 and a horizontal overhanging portion 32 which extends above and over the work table 24. The horizontal portion 32 terminates in an enlarged hollow head 34. Within this head and within the adjacent portion of the horizontal portion 32 are located the upper spindle assembly 38 and the spring mechanism. 36. The upper spindle assembly 38 is located in alignment with the lower spindle assembly The head 34 is normally closed by a cover plate Ml, which is held in position by means of screws 42. The hollow head 34 comprises upper and lower walls 44 and 46 which carry bearings 48 in which the spindle 50 of the upper spindle assembly 38 reciprocates. The spindle 56 carries at its lower end a chuck 52 which is adapted to receive the upper end of the saw blade 54 which is secured thereto by means of the Wing nut 56.
The spindle 50 is cut away on opposite sides to provide fiat surfaces 58 (Fig. 6) located at a portion of the spindle 50 which is always within the head 34. A pin 60 extends through the spindle 50 beyond the faces 58. A bell crank lever 62 consisting of two similar members riveted together and maintained in spaced relation, as indicated at 64, is pivotally mounted upon a pin 66 which extends across the horizontal hollow member 32 of the arm 26. The bell crank lever 62 includes a short arm 68 which extends down-' wardly and a long arm Ill which extends horizontally towards the spindle 50. The two spaced members of the bell crank lever 62 are located on opposite sides of the spindle 5U engaging the op- 50 against rotation. The extremities 12 of these members are slotted, as indicated at M, to receive the projecting ends of the pins 60.
The short arm 68 is pivotally connected to a link 16 by a rivet pin 18. The opposite end of the link 16 is connected toone end of coil spring 80, the other end of which is hooked to a threaded bolt 82 which extends past the spindle 56 through an opening 84 in the cover plate 40. The outwardly projecting portion of the bolt '82 is provided with a. wing nut 86 so that the tension of I posite faces 58 thereof and holding the spindle I the spring may be adjusted at will. The bolt 82 is held against rotation by suitable means, for example, its underside may be flattened as indicated at 88 (Fig. 6) and the opening 84 may be formed with a corresponding flat side in engagement with the surface 88. It will be seen, with particular reference to Fig. 6, that the long arm 10 of the bell crank lever 62 is offset, as indicated at 90, so as to enable the bolt 82 to be located to one side of the spindle 50.
A vertical rod 92 is adjustably mounted on the overhanging horizontal portion 32 of the arm 26, this rod being slidably and rotatably mounted in an opening in a boss 94 formed on one side of the arm 26. The rod 92 is held in desired adjusted position by means of the thumb screw 96. At its lower end the rod 92 carries a block 98 which is slidably mounted on the rod 92, being positioned thereon in any desired location with the aid of a set screw I00. The block 98 is provided with an internal bore I02 which enters into a projecting nozzle I04 which is adapted to be directed towards the work to blow the sawdust away.
Below the block 98, the rod 92 carries a supporting member I08, upon which is mounted a roller I96 provided with a V groove in which the blade 54 is received and guided. The supporting member I08 is adjustably mounted on a plate IIO by means of a knurled nut H2. The plate III] is provided with a slot II4 through which extends a bolt II 6 whereby the plate is secured to the lower end of the rod 92 in desired position of adjustment. The plate I I0 carries downwardly extending curved legs II8 which are adapted to engage the work and prevent it from being elevated by the return stroke of the blade 54.
The work table 24 is mounted upon a table support I22 which is secured to a bracket on the housing I6 by means of bolts I20. The table support I 22 is provided with upwardly directed concave arcuate guides I24 and the table 24 is provided with corresponding convex arcuate guides I26 adapted to cooperate therewith. Consequently, the table can be tilted about the common axis of the arcuate guides I24 and I26, into any desired inclination with respect to the saw blade.
The table may be locked in desired position of adjustment by handle and cam means designated generally by the reference numeral I28. The table 24 is provided with an insert I29 which is located in substantial alignment with 'thespindle 50 and the lower spindle assembly 22, this insert being provided with a kerf through which passes the blade 54. This insert is removable to enable the machine to be used with tools other than a ribbon saw blade, such as a file, saber saw, or sander, for example. It may be noted that when thus employed, the overhanging arm 26 may readily be romoved by removing the bolts 28, thereby providing unlimited work room above the table. When thus used, the tool is rigidly mounted in the lower spindle assembly 22.
Referring more particularly to Figs. 3 and 4, it will be noted that the housing I6 provides a cylindrical crank case chamber I30 which is provided with a vertical boss I32 on its upper side. Bearing members I34 are located within the boss for slidably supporting the lower spindle I36 of the lower spindle asembly I22. The upper end of the spindle I36 is provided with a chuck similar to that carried by the upper spindle 50.
The spindle I36 is provided on one side with a horizontal rectangular slot. I 38. Opposite this slot it is provided with a flat surface I40. A horizontal guide block I46 is rigidly seated within the slot I38 and is held therein by means of a bolt I42 which extends through the block I46 and is threadedly received in a bore I44 which extends through the spindle I36 from the slot I38 to the flat face I40. The bolt I42 is securely locked in position by means of an internally threaded sleeve I86 which is provided with a hexagonal portion I88 near its inner end and a cylindrical portion I projecting outwardly therefrom.
The guide block I46 is provided with a longitudinal bore I48 of cylindrical section, which bore is open to the outer side of the block I46, that is, to the left side as viewed in Fig. 4. A cylindrical block I50 is located within the block I46 so as to reciprocate freely therein in a horizontal direction. A crank pin I54 extends freely into a horizontal bore I52 in the block I50. The manner in which the crank pin I54 is actuated will be hereinafter described. It will, however, be noted that when this crank pin is rotated it effects the reciprocation of the spindle I 36 in the upward and downward direction. At the same time Una block I54 reciprocates horizontally in the bore I48 in the block I46. It is to be noted that the block I50, being held against movement about the axis of the spindle I36 by engagement with the crank pin I54, effectively prevents rotation of the spindle I36.
The left-hand side of the housing I6, as viewed in Fig. 4, is closed by means of a cover I58, a gasket I60 being interposed between the flange of the cover and the adjacent flange of the housing. The cover I58 has a transverse bore I62 through which extends a drive shaft I64, the shaft being supported by suitable bearings I66. The cover I58 comprises a cylinder I68 at right angles to the bore I62. I
A piston stem I'I0 extends downwardly through an opening in the lower end of the cylinder I68 and contacts a cam I'I2 formed on the drive shaft I64 so as to effect reciprocation of the piston stem. The piston, which is provided with a suitable sealing cup at its upper end, is biased downwardly by a spring H4. The cylinder I68 is provided with air passages I76. The outlet of the pump is connected by a flexible hose I18 to a nipple on the block 98 which connects to the internal bore I02 and, consequently, to the projecting nozzle I04. The flexible conduit Il8 may preferably extend into the base I0 and through the overhanging arm 26 to a position adjacent the block 98.
The crank pin I54 is rigidly mounted in a balanced crank I 80 which, as best seen in-Figs. 3 and 4, consists mainly of ,a counterweight portion located on the side of the shaft I64 which is opposite the position of the pin I54. The crank member I80 is rigidly mounted on the inner end of the shaft I64. The outer end of the shaft I 64 carries a variable speed pulley I82 which is driven by means of a V belt I84 from a corresponding variable speed pulley (not shown) on the motor I2. v
The cylindrical portion I90 of the sleeve I86 serves as an abutment for the hook-curved end I92 of a fiat spirally wound spring I94. The inner end of the spring I94 is mounted in a transverse slot I 96 of a shaft I98 upon which it is held by means of nuts 200. The shaft I98 is rotatably mounted in a boss carried by the cover 292 which closes the end of the housing 204 opposite the cover I58. The shaft I98 is provided at its outer end with a hexagonal head 206 which is received in a hexagonal opening 2 I4 in a handle 208.
The handle 268, which is slidably mounted on the shaft I98, is recesed to accommodate a spring 2 Nil This spring, which is accommodated around the shaft iSB, abuts against the inner side of the head 2% and against the shoulder N2 of the handle 2E8 so as to force the handle inwardly towards the cover 282. The innermost end 213 of the handle 2%, which normally bears against the cover 262, is provided with a circumferential series of openings 226, as best seen in Figs. 4 and '7. The cover 202 has rigidly mounted therein an outwardly projecting pin 22 which is adapted to enter any of the openings 22!? which may be presented to it. It will be readily understood that if the handle 288 is pulled outwardly it may be rotated in either direction so as to adjust the tension which the spring 194' applies to the sleeve I86. When the tension is thus regulated, the handle 208 is allowed to move inwardly under the action of the spring 2 l6 and the pin 222 enters the adjacent opening 220 so that the tension of the spring is maintained in the desired condition.
The weighted crank N38 is arranged to provide a substantial balance for the moving systemcomprising the spindle 136, the blade 54 and the spindle 50. This balance is necessarily somewhat approximate, because the load experienced by this system in moving downwardly varies widely, depending upon whether or not the blade 54 is cutting.
In the ordinary operation of tool of this kind, the spindle 22 is pulled down forcibly by the crank pin I54 and when the crank pin i5 1 passes through its lowest position. the downward load on the spindle is released and the spindle is free to move relative to the crank pin I54 Within the limits of the lost motion necessary between these elements for working fit. This relative freedom and the initiation of the return movement of the tool, due to the tension of the spring 8!! and also to the drive by the crank pin, result in whipping and irregular movements of the blade Be.
In my present structure such defects are completely avoided because the blade 54 is maintained under tension at all times. Further, the springs 80 and H94 counter-balance each other to a considerable extent and the major operating force is that applied by the crank pin I54 which is, in fact, responsible for practically all movements, both up and down, of the blade 54.
In practice, I prefer that the upward force exerted on the blade by the spring 80 should be approximately equal to the downward force applied to the blade by the spring 19%. However, it is not necessary to measure these forces since the machine is adapted for very perfect adjustment in the following manner. The wing nut 86 is tightened in order to apply a reasonable degree of tension to the spring 8t. If no tension is applied to the spring Hi l and the motor I2 is started, the machine will work with a pronounced noise due to whipping and irregular movements of the blade and also due to lost motion between the pin W4 and the spindle I36. If, now, the spring I95 is tensioned by suitable displacement of the handle 258, the noise will lessen and lessen progressively and can be substantially eliminated. If too much tension is applied to the spring I9 5, the operation again becomes noisy and this occurrence indicates that the handle 26% should be backed up again to reduce the tension of the spring 18 to a degree which is approximately equal to that exerted on the spindle 5G by the spring Bil.
It is to be noted that both these springs adapted to apply a very uniform tension upon the'two spindles with which they are associated. That is, the tension of a spring like the spring 85 increases with extension. This effect can'be minimized by using a very long spring. I am able to use quite a short spring 85 while obtaining very uniform tension on the spindle 5i) by my new feature of employinga bell crank lever Bil of very considerable leverage. The coil type of spring Hi4 provides the eifect of a relatively long spring while occupying a relatively small space.
Although the invention has been disclosed in connection with the specific details of a preferred einbcdimezzit thereof, it must be understood that such details are not intended to be iimitative of" the invention except insofar as set forth in the accompanying claims.
Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:
1. In a scroll saw, the combination comprising, a base, an overhanging arm mounted on the base having a substantially horizontal hollow portion at its overhanging end and a cover closing said hollow portion, a member extending vertically through the hollow portion .near said end and mounted to reciprocate therein, a bell crank within the hollow portion pivotally mounted rearwardly of said member, said bell crank having a long substantially horizontal arm extending forwardly of the pivotal mounting and a relatively short substantially vertical arm, a link pivotally attached to the outward end of said vertical arm, means to connect said long arm to said member, a horizontally positioned spring secured to said link, and manually operable means outside of said hollow portion to adjust the bias of said spring, the last said means comprising a threaded member secured at one end to said spring and projecting through an opening in said-cover, and the portion of said threaded member projecting through said cover having a complementary threaded manually adjustable member threaded thereto.
2. In a scroll saw blade reciprocating unit, in
combination, a housing and a cover to close said housing, a reciprocable member extending into the housing, a spiral spring having a hooked outer end engaging said reciprocable member to bias said member downwardly, a control shaft extending into said housing and engaging the inward end of said spring, control means outside of said housing adapted by manual manipulation to rotate said controlshaft, and means to secure said control shaft in any manually set position, said control shaft journaled through said cover and extending beyond the outer face thereof, said control means secured to the outer end of said control shaft and said cover carrying the means to secure the control shaft in any manually set position, whereby the control shaft, the spiral spring, the control means, and
the means'to secure the control shaft are all removable from the saw blade reciprocating unit as a single unit with said cover.
'IHERON L. HEDGPEfII-I.