US1725861A

US1725861A - Tapering mechanism for sawmill knees

Info

Publication number: US1725861A
Authority: US
Inventors: William B Grueter
Original assignee: PRESCOTT Co
Current assignee: PRESCOTT Co
Priority date: 1927-09-09
Filing date: 1927-09-09
Publication date: 1929-08-27
Anticipated expiration: 1946-08-27

Description

Aug. 27, 1929. w, B, GRUETER V' f 1,725,861

l TAPERING MECHANISM FOR SAWMILL KNEES Filed Sept. 9, 1.927 5 Sheets-Sheet l Aug. 27, 1929. w. B. GRUETER 1,725,861

TAPERING MECHANISM FOR SAWMILL KNEES Filed sept. 9. 1927 s'sneets-sneet 2 3. w Q /ff ATTORNEY.

Aug. 27, 1929.

W. B. GRU ETER TAPERING MECHANISM FOR SAWMILL KNEES Filed Sept. 9, 1927 3 Sheets-Sheet 3 IN VEN TOR.

MQW

A TTORNE Y.

Patented Aug. 27, 1929.

UNITED' STATESL PATENT'. OFFICE.

WILLIAM B. GRUETER, or Mnivorirnnn, MICHIGAN, nssrsivon 'ro THE rnnsco'r'r COMPANY, or ivrnnoriinnn, rammel-in, .a conrona'rron OFKMICHIGAN. f

TAPERING MECHANISM FOR SAVJMLL KNEES.

Application filed September' This invention relates to tapering mechanism for sawmill knees and is especially designed and adapted for organization with the modern type of' electrical sawmill equipment.

One object of the present invention is to provide tapering mechanism of the type driven by an electric motor, and which is easily controlled and operated to effect automatically any one of a plurality of different predetermined tapering movements. In other words, each-knee may be independently moved or advanced by its electric motor through any selected one of a plurality of dilierent predetermined distances, the electric motor being automatically shut off after the knee has traveled or advanced through the selected distance A further object is to make provision for the employment, when desirable, of automatic stopping means which positively prevents coasting or any further movement of the knee after it has completed the selected tapering movement.

A still further object resides in the provision of tapering mechanism having these advantages and capacitiesand which is of simple and durable construction, reliable, eilective and accurate in operation, easily controlled and adapted to be organized with facility and at a minimum of expense with the most advanced and modern type of electrical sawmill equipment.

Other objects and advantages reside in certain novel features of the construction, arrangement and combination of parts which will be hereinafter more fully described and particularly pointed out in the appended claims, reference being had to the accompanying drawings forming a part of this specication, and in which Figure yl is a diagrammatic view in elevation showing a sawmill knee of anl electric rig equipped with a control for tapering mechanism embodying thevpresent invention, the sawmill carriage and the taper drive being shown partly in transverse section.

Figure 2 is a view partly in elevation and partly in section `taken on line 2 2 oi' Figure 4.

Figure 8 is an enlarged fragmentary view showing the control for the tapering mechanism in side elevation, parts being broken away for the sake of illustration.

Figure 4 is a similar view but shows the 9, 1927. Serial No. 218,400.

complete outline of the parts of the control illustrated in Figure 3.

Figure 5 is a diagrammatic view showing the electric circuit provided for the control or the electric moto-il which drives the tapering mechanism.

Taperz'ag means proper.

Referring to the drawings, numeral 1 designates a sawmill carriage which has a suitable number of the usual head blocks 2 on each of which a knee y3 is mounted for sliding movement toward and away from the saw line. To simplify the illustration only one knee is shown but, of course, any suitable number may be provided. A tapering screw 4 is mounted for, and constrained to, rotation in bearings provided therefor on each knee 3 and on this tapering screw 4 a nut 5 is iitted, the nut 5 having a threaded bearing interengageable with the threads of the screw and being constrained to rectilinear movement when the screw is rotated by virtue oit' its engagement with guideways 6 provided on knee (see Figure 2). As shown, the nut 5 is in the form of a very substantial block or cross bar like structure and while primarily and principally it has the usual mechanical function of the ordinary nut of avta'pering mechanism, it also serves as a mounting for certain of the control parts as will hereinafter more clearly appear. A link 7 has one end pivotally connected to the 'nut 5 as at 5 and has its other end pivotally connected to a rack bar 8 as at .8 whereby the link 7 serves to connect the nut y5 and the rack bar 8 in the usual manner. In accordance with conventional practice the rack bar 8 is slidably interitted with the knee 3 vas indicated at 9 (see Figure 2). The rack bar 8 is engaged with'a pinion 10 lixed on aset shaft 1l and driven in the usual manner under the control of the usual set works (not shown). When the knees are to be advanced simultaneously they are actuated from the set shaft which causes each rack bar 8 and its knees 3 to slide as a unit on the guides 2CL of the head block. When it is desired to impart tapering movement to any one or more of the knees, it is necessary to cause the knees to slide relative to the racks 8 and this isv accomplished by turning the screw 4, which causes the screw to travel through the nut 5., the nut 5 being held by virtue of its connection with the rack 8. While the screw 4 is mounted to rotate on the knee it cannot move axially relative to the knee so that the knee must partake of the axial movement of the screw 4.

For the purpose of rotating the screw 4 to provide for this tapering movement an electric motor 15 is secured on the knee and has its armature shaft 16 coupled as at 17 with a shaft 18, which projects into and is journaled in a gear casing 19. Within the casing 19 a pinion 20 is fixed on the shaft 1S and meshes with a gear wheel 21 connected as at 22 to an extension of the screw 4. This connection 22 is a slip connection which, while normally providing for the transmission o1" the motion of the gear wheel 21 to the extension of the screw shaft is nevertheless designed to slip when the gear wheel is turned from the electric motor and the screw is held against motion by virtue of the engagement with the nut of the socalled home stops77 or abutments on the knee, these parts engaging in either extreme position of the knee, that is, when the knee is advanced or retracted as far as it may be by the tapering mechanism.

The construction as thus far described is` similar to that set forth in detail in the copending application of Ross E. Langill and William B. Grueter for sawmill dogs, filed September 13, 1926, Serial No. 134986, towhich application reference is made for a detailed disclosure of such features. The present invention also contemplates the use of various other types of mechanism of this character and is particularly adapted for use with the means shown in the co-pending application of Ross E. Langill and William B. Grueter for sawmill dogs filed September 16, 1926, Serial No. 56,590.

General outline of taper motor control and stop.

It will now be appreciated that the present invention starts with a sawmill knee tapering mechanism of the type driven by an electric motor. In its broadest aspect the present invention consists in organizing with such tapering mechanism and its motor, a control for the motor governed by the motion of the knee and acting to shut oft the motor automatically after it has operated to such extent as to impart any selected one of a plurality of different predetermined taper'- ing movements to the knee.

In gene-ral the control comprises a plurality of normally closed limit switches 7 0, 71 and 72, each including a contact plate 99 and a control plunger 100, mounted on the knee 3 and organized with the motor 15 and with a plurality of normally open manually operable switches, 66, 67 and 68, see Figure 5, (which may be push button switches) located within convenient reach of the operator and adapted to be selectively closed to complete the motor circuit through any particular' one of the limit switches. A trip 110 is fixed to a stationary part of the tapering mechanism, usually the nut, and is positioned to successively engage with and open the limit switches as the limit switches move past the same when the knee is moved under the influence of the tapering mechanism. The motor continues to operate until the trip 110 opens the particular limit switch through which the motor current has been closed by

switches

66, 67, or 68 whereupon the motor circuit is broken and the motor stops. Thus selection of a manually

operable switch

66, 67 or 68 determines the limit switch which is to control the shutting off of the motor. Opening ot any limit switch except the one through which the motor circuit is closed has no'eifect on thc operation.

Where desirable an automatic and positive stop is pro-vided `to prevent the knee from coasting` or advancing under the influence of momentum or otherwise after the motor has been shut off. Briefly, this stop consists of a pair of stop'bars 115 suitably mounted on thc knee and having a tooth or stop 115 for each limit switch (and consequently for each intermediate stopping position), the teeth being engageable with suit-able lugs 130 provided on the nut 5.V The stop bars 115 are biased to a position wherein one of the teeth of each will engage a lug 130 of the nut 5 but are automatically released by means of a solenoid 55 operatively associated with the stop bars and electrically connected with the motor circuit whereby, when the motory is running to advance the knee, the stop is released and as soon as the motor is shut off the stop is permitted to .become effective to prevent further advance of the knee.

Specific features of taper motor control.

Y Briefly, the taper motor control comprises a forward and a reverse magnetic contacter' control, the forward contacter operating when energized, to close the motor circuit and cause the motor to run forwardly and the reverse contactor operating, when energized, to close the motor circuit in such manner as to reverse the motor. A single push button switch is provided for regulating.

the opening a-nd closing of the reverse contactor circuit. The opening and closing ot the forward contactor circuit is regulated by the plurality of limit switches and pushbutton switches elsewhere described herein.

As shown in Figure 5, wherein one system of wiring is illustrated, the motor circuit for the motor 15 receives its current from a suitable source of supply, as for instance, from the power lines or wires 25, 26 and 27. A wire 28 connects the wire 25 directly with a terminal 29 of the motor. he terminals 30 and 31 of the motor are connected with the power lines 26 and 27 netic contactor may beV energized to cause through conventional magnetic contactors which, with the other' instrumentalities to be hereinafter described, provide for the foi'- ward and reverse actuation of the motor l5. Thus the wire 26 is connected by wires 32 and 32L with a terminal 33 connected as at 33a with one of the contacts of the forward contactor 35. A Contact 36 co-acts with the Contact 34 and is connected by conductors 37a and 37 with the motor terminal 30. The motor terminal 31 connects by wires 38, 39 and 40 with a contact 4l of the contactor 35. A cont-act 42 which co-acts with the contact 4l connects by a conductor 43 and a wire 44 with a wire 45 which is electrically connected with the power line 27 The contactor 35 includes the usual coil 46 having one terminal 47 connected by wires 48 and 49 with a wire 50, the wire 50 being connected with the wire 32. rlihe other terminal 5l of the contact coil 46 is connected by

wires

52 and 53 with a terminal 54 of the solenoid 55 of the electro-magnetic release for the stop which will be hereinafter more fully described. The other terminal 56 of the soienoid 55 is connected by a wire 57 to a contact bar 96 common to the limit switches 70, 7l and72 and coacts with the movable contact members 99 of these limit switches.

Tires

58, 59 and 60 are electrically connected to and lead from the contact members 99 of the switches to contacts 62, 63 and 64 of push button or manually

operable switches

66, 67 and 68 located at any point or control station within convenient reach and control of the operator, usually the setter. A wire 6l is also electrically connected to the wire 57V and leads to a contact 65 of a push button switch 69 located at the same point of control or control station as the

switches

66, 67 and 68. The construction, operation and position of these

limit switches

70, 71 and 72 will be hereinafter more fully described. The manually

operable switches

66, 67, 68 and 69 also have contacts 62, 63a, 64a and 65a and depressible bridging contact members 76, 77, 78 and 79, which when depressed serve to electrically connect the contacts 62 and 62a, 63 and 63a, 64 and 64a, or 65 and 65a. The contacts 62a, 63a, 64a, and 65a are connected by wires 80, 81, 82 and 83 with a wire 84 which connects with a wire 84a, the latter connecting with the wire 44 as at 44a and consequently also with the wire 45 which leads to the power line 27.

In other words while the limit switches 70, 7l and 72 are connected in series with the push-button switches, 66, 67 and 68 respectively, the several sets of series connected limit and push-button switches are connected in parallel across the forward contactor control circuit. By depressing any one of the bridging contact members of the

switches

66, 67, 68 and 69 the coil 46 of the forward magthe contacts 34 and 42 to engage the contacts 36 and 4l, thereby completing the motor circuit and starting up the motor to initiate the tapering movement. For instance, if the switch 66 is closed, the current will flow through the

wires

32, 50, 49 and 48, to the terminal 47, then through the contactor coil 46 to its other terminal 5l and thence through the

wires

52 and 53 to the terminal 54, through the solenoid 55 and wire 57 to the wire 58, across closed limit switch to the contact 62 of the switch 66 and through the bridging contact member 76 to the contact 62a. From the Contact 62"L the current flows through

wires

80, 84, 84a, 44 and 45 to the power line 27. gizes the contactor 35 to close the motor circuit as described. If, however, the limit switch 70 is opened the contactor coil 46 will be deenergized and the motor circuit broken.

The present invention proposes to open This enerthe limit switches 70, 7l and 72 automaticaliy and successively in a manner which will be hereinafter more fully described. As soon as the limit switch in series with a depressed push-button switch and consequently through which the motor circuit has been closed, is opened, the motor is shut oif. Of course, if

the push-button switch 68 is depressed nothlng will happen when the limit switches 70 to the knee and the several movements may have any desiredamplitude. ln the present instance the 6 inch tapering movement is controlled by the push-button switch 69, which is connecte-d across the forward contactor circuit in parallel with the switches ated with switch 69 for the reason that upon the completion of such movement one of the home stops engages the nut 5 to prevent any further movement of the knee. 0f course, the motor continues to operate until the push button 69 is released and the slip connection 22- takes care of this. The same is true of the other extreme adjustment which is had when the knee is retracted as far as it may be. The retraction of the linee is provided for by reversing the motor 15. The reversing of the motor is under the control of a push button switch 90 incorporated in the circuit of the usual contactor 91, so that when the switch 90 is depressed and closed, the contactor 91 is energized and the motor circuit closed to reverse the motor.

rlie push-

button switches

66, 67, 68, 69 and llO f may be located at any suitable point oit convenient control, but it is essential that the

limit switches

0, 71 and 72 be mounted on the knee, as it is proposed to utilize the relative movement of the knee and nut to automatically open these limit switches.

As shown in Figures 2, 8 and 4 the limit switches are located at spaced points along the knee in the direction oi" movement thereof and are mounted ina suitable housing carried by a knee. rlhe limit switches com` prise a contact bar 9G insulated and supW ported in a liked position within the housing 95 by means of bolts and nuts 97 and insulating strips 98. insulating bushings may also be provided around the bolts so that the contact bar 96 is entirely insulated from the housing and from its supporting means. One section of each of the

wires

58, 59 and 00 connect with this contact bar 90, the contact bar 96 serving as a common contact or terminal for all of the switches. Each switch also has a movable contact member 99, the movable contact members being connected with the other sections of the

wires

58, 59 and 60, each movable contact 99 being supported upon and projecting laterally l'rom the lower end of a guide plunger 100 slidably interiitted into a socket 101 provided in the housing 95. The plunger 100 and its socket 101 are ot non-circular form to prevent rotation ot the plunger. As illustrated in Figure 2 the movable contact 99 of each limit switch is secured to the lower end oi2 its plunger 100 by means of a stud 102 threaded into the lower end of the plunger 100 and passing through an opening in the Contact 99. Nuts 103 are threaded on each stud 102 and clamp the contact 99 between insulating washers 104 mounted on the stud and arranged on the opposite sides of the contact 99. An insulating bushing 105 is alsoV provided between each contact 99 and its stud 102. r1`he stud 102 projects down below the nuts 108 and into the upper end of a coil spring 106,

`which is tensioned to retain the Contact 99 engaged with the contact bar 96 and the plunger 100 elevated.

To providel lior the depression of the plunger' 100 and the automatic opening of the limit switches, a trip or cam is fixed to or integral with the nut 5 and has its lower end positioned to successively engage the upper ends of the plunger 100 as the knee moves relative to the nut. rlhe lower end oi this trip or cam 110 is double beveled as shown in. Figures 3 and 4f and the upper ends ot the plunger 100 are similarly formed. his permits the plunger 100 to pass the cani or trip 110 it the opening or" the lirst or second limit switch does not stop the motor. Such conditions would exist if, 'for example, the push button 68 were depressed.

Automatic posit/oe stop. In the present embodiment of the invention, the stop provided to prevent further movement of the knee when the motor is shut oil?, comprises a pair of stop bars having down-turned ends 116 pivotally connected to arms 117 and 118 fixed to

shafts

119 and 120 rotatably supported in the side members oi' the knee. The shaft 119 has a crank arm 120 fixed thereto and pivotally connected as at 21 to the curved end 121 ot link 122. The opposite end oi' this link 122 is pivotally connected to an arm 123 of a bell crank lever 124, the bell crank lever 12d having its other arm 125 fully ulcrumed as at 126 on the casing 127 of the solenoid 55. The core 128 of this solenoid is pivotally connected as at 129 to the arm 125 of the bell crank lever 124. The straight portions of the.stop bars 115 are notched to provide teeth or projections 115%, there being one such tooth or projection for each limit switch, that is,` for each intermediate position or each intermediate tapering movement of the knee. r[hese projections 115a are engageable with lugs 180 provided on the nut 5. Whenever any one of the push-

button switches

66, 67, 68 or 69 are depressed, the solenoid 55 is energized as previously pointed out and consequently the core 128 is pulled upwardly to rock the bell crank lever 124; and push the crank 122 to the lett, as viewed in Figure 4;, thereby rocking the shait 119 in a counterclockwise direction as viewed in Figure l and elevating the stop bars 115 to disengage the projections of the stop bars from the lugs of the nut.` As long as the motor is running the solenoid is energized and, consequently, the stop bars vare elevated. However, as soon as the appropriate limit switch is opened and the motor circuit is broken the solenoid is deenergized and the stop bars drop under the action of gravity to cause the proper projections thereoi: to engage the lugs of the nut. 0f course, the stop bars when elevated move with the knee so they are always properly positioned relative to the nut. As the projection of the stop bars are beveled off one way, they ride over the projection V'freely when the motor is reversed to retract the knee.

Summary of operation.

From` the foregoing it will be understood that any one of a plurality of tapering movements may be imparted to a knee by depressing the proper push-button switch, (S6, 67, (58 or 69. 1f the push-button switch (39 is depressed the knee is advanced until a portion thereoi2 (the so-called home stop) engages the nut 5, whereupon further movement of the knee is prevented. If any one of the

switches

66, 67, or 68 is depressed the stop bars are raised and disengage from the lugs oi the nut and the knee is advanced until the

limit switch

70, 71 or 72, through which the motor circuit has been closed, is opened. The opening of the appropriate limit switch breaks the motor circuit and also deenergizcs the magnetic control for the stop bars whereby the motor is automatically shut oilF1 and the proper teeth of the stop bars drop into engagement with the lugs ol the nut. The knee may be retracted -from any advanced position by depressing the push-button switch 90 which reverses the motor and consequently reversely moves the knee. In this event the knee moves back until its other home stop engages the nut 5, whereupon further retraction of the knee is prevented.

'Ihe invention claimed is:

l. In combination, sawmill knee tapering means, an electric motor v for driving the same, a plurality of limit switches mounted on the knee and organized with the motor circuit, selective means within reach of the operator for closing the motor circuit through any one of the limit switches, and a trip mounted on a stationary part of the tapering means and operating to successively open the limit switches as the knee ymoves under the inliuence of the tapering means.

2. In combination, sawmill knee tapering means, an electric motor for driving the same, a plurality of limit switches mounted on the knee at points spaced along the line oi movement of the knee and organized with the motor circuit, a plurality of manually operable switches located within reach of the operator and organizedwith the limit switches and with the motor circuit and selectively operable to close the motor circuit through any one of the limit switches, and a fixed trip mounted to engage and open the limit switches successively as the limit switches move past the same when the knee moves under the influence of the tapering means.

, 3. In combination, sawmill knee tapering means, an electric motor for driving the same, a plurality of limit switches organized with the motor circuit, a plurality of manually operable switches organized with the limit switches and with the motor circuit and selectively operable to close the motor circuit through any one of the limit switches and means for successively opening the limit switches as the knee moves under the inliuence of said tapering means.

4. In combination, sawmill knee tapering means, an electric motor for driving the same, a plurality of limit switches organized with the motor circuit, selective means for closing the motor circuit through any one of the limit switches and means :t'or successively opening the limit switches as the knee moves under the influence of said tapering means.

5. In combination, sawmill knee tapering means, an electric motor for driving the same and, control means for the electric motor governed by the motion of the knee and acting to shut otl the electric motor automatically after the motor has operated to such extent as to impart any selected one of a plurality of different predetermined tapering movements to the knee.

6. lThe y combination with sawmill knee tapering means and an electric motor for driving the same, of a plurality of limit switches organized' with the electric motor and operable, when suitably actuated, to stop the operation of themotor, a plurality of manually operable switches organized with the electric motor and with the limit switches whereby the manually operable switches may be manipulated to select any one of a plurality of tapering movements and means operable upon the completion of any tapering movement for suitably actuating the appropriate limit switch.

7. A control for sawmill knee tapering means having an electric motor for driving the same and comprising a plurality of normally open manually operable switches, a plurality or' normally closed limit switches, said switches being electrically connected with each other and with the electric motor and a trip cooperable with the limit switches upon tapering movementoil the knee.

8. In combination, a knee, a rotatable screw mounted on the knee, a nut engaged with the screw, setting means connected with the nut, and maintaining the same fixed, relative to the knee, an electric motor mounted on the knee and geared to the screw whereby the motor may be utilized to cause the knee to move relative to the nut and'to v the setting means, a plurality of normally closed limit switches mounted on the knee, organized with the electric motor and adapted, when opened, to stop the operation of the motor, a plurality o'll normally open manually operable switches organized with the electric motor and with the limit switches and operable to close the motor circuit through any one of the limit switches and thereby to select any one of a pluralitybf tapering movements, and means on the nut cooperable with the limit switches for successively and automatically opening the limit switches when the knee is moved relative to the nut.

9. In combination, sawmill knee tapering means, an electric motor for driving the same, selective means for causing the electric motor to operate to such extent as to impart any one of a plurality of predetermined tapering movements to the knee, and separate means for positively stopping move-A ment of the knee at the completion of any selected tapering movement.

l0. The combination with sawmill knee tapering means and an electric motor for driving thev same, of a plurality of limit switches organized with the electric motor, operable, when suitably actuated, to stop the operation of the motor, a plurality of manually operable switches organized with the electric motor and with the limit switches wherebymanually operable switches may be manipulated to select any one oi a plurality of tapering movements and a positive stop Aautomatically movable to stopping position upon completion of any tapering movement. l1. The combination with sawmill knee tapering means and an electric motor for driving the same, ot a plurality olf limit switches organized with the electric motor and operable, when suitably actuated, to stop the operation of the motor, a plurality of manually operable switches organized with the electric motor and with the limit switches whereby the manually operable switches may be manipulated to select any one of a plurality of tapering movements, a positive stop biased to stopping position and an electro-magnetic release ior said stop energized when the motor is operating and deenergi'zed when the motor is stopped.

12. A controlv for sawmill knee tapering means of the type driven by an electric motor, and comprising stopping means for arresting tapering movements o' the knee and an electro-magnetic control for the stopping means organized with the electric motor so as to be governed in its action by the operation oi the motor.

13. A control for sawmill knee tapering means of the type driven by an electric motor and comprising stopping means for arresting tapering movements of the knee and a control for the stopping means organized with the elect-ric motor so as to be governed in its action by the operation oi the motor. v

14. A control for sawmill knee tapering means and comprising stopping means for arresting tapering movements ot the knee and an electro-magnetic control for the stopping means.

15. A cont-rol for sawmill knee tapering means comprising stopping means operable to stop the knee after any one of a series of predetermined movements and an electromagnetic control for the stopping means.

16. A control for sawmill knee tapering means comprising a stop bar having a series of stops adapted to be utilized selectively to stop the knee after any one et a series et predetermined movements and a control tor the stop bar,

17. In combination, a knee, a screw rotatably mo-unted on the knee, a relatively fixed nut engaged with the screw, an electric motor mounted on the knee and geared to the screw whereby the motor may be utilized to cause the knee to move-relative to the nut, a plurality of limit switches mounted on the knee and organized with the motor circuit, selective means for closing the motor circuit through any one of the limit switches anda trip mounted on the nut and cooperably engageable with the limit switches for opening the same one after the other as the knee and limit switches move past the trip.

18. ln combination, sawmill knee tapering means, an electric motor for driving the same, a plurality of limit switches mounted on the knee and organized with the motor circuit, a depressible operating element associated with each limit switch, selective means for closing the motor circuit through any one ot the limit switches and a trip mounted on a stationary part of the tapering means engageable with the operating elements of the limit switches upon movement of the knee.

19. ln combination, sawmill knee tapering means, an electric motor for driving the same, a plurality of limit switches mounted on the knee and organized with the motor circuit, said limit switches including a contact bar, a plurality of movable contacts coacting with'the bar, spring means urging the movable contacts to engage the bar, a depressible plunger for each movable Contact, such plunger, when depressed, disengaging the movable contacts from the bar, selective means i'or closing the motor circuit through any one of the limit switches and a trip mounted on the nut and engageable with the plungers for depressing the same vupon movement oi the knee.

20. ln combination, sawmill knee tapering means, an electric motor for driving the same, a control for the electric motor governed by the motion of the knee and acting to shut ofi the motor automatically after the motor has operated to such extent as to impart any selective one of a plurality of diit'erent predetermined tapering movements to the knee, a pair of stop bars mounted on the knee and adapted to engage a stationary part of the equipment to positively stop and hold the knee in any one of its intermediate positions and an electro-magnetic release for the stop bars organized with the motor circuit so as to be energized when the motor is running 'forwardly and deenergized at other times.

21. A power taper for a sawmill knee comprising a motor, a plurality of controls therefor and means governed by the motion of the knee for automatically rendering inoperative any operated control to thus impart variable tapering movement to the knee.

22. A power taper for a sawmill knee comprising a motor, a plurality of controls therefor and means for automatically rendering inoperative any operated control to thus impart variable tapering movement to the knee. y

In'witness whereof, I hereto aliix my signature.

WILLIAM B. enunrnn.