US3183950A

US3183950A - Multiple length defect trim saw

Info

Publication number: US3183950A
Authority: US
Inventors: Charles A Sherman
Original assignee: Individual
Current assignee: Individual
Priority date: 1963-10-23
Filing date: 1963-10-23
Publication date: 1965-05-18
Anticipated expiration: 1982-05-18

Description

May 18, 1965 c. A. SHERMAN IUL'I'IPLE LENGTH DEFECT TRIM SAW Filed Oct. 23, 1963 MULTIPLE LENGTH DEFECT TRIM SAW Charles A. Sherman, 3914 S. 7th.St., Tacoma, Wash. Filed Oct. 23, 1963, Ser. No. 318,348 Claims. (Cl. 144'-2) This invention relates to an apparatus for cutting de- {fects from lumber and in particular to an improved control means for automatic operation or" such apparatus. [The advantages of an automatic lumber defect trim saw were related in US. Patent 3,044,508, issued to me on July 1 7, 1962. It sufiices to saythat valuable sect-ions of lumber can be easily upgraded by the utilization of such a saw to cut away detects.

In the past, automatic defect removal was limited to outting the boards at the point where the defect indicating means was located by the grader or at a fixed offset from this point and, in either case,'ia second sawing operation a was required to cut the remaining upgraded board to a standard length.

It is the object or this in-verition to provide a means for sensing the defective section indicating means and to perform the cutting operation at a point ahead of such means which will result in an upgraded board of a standard length once the defective section has been removed by such a cutting operation.

It is the further object of this "invention to provide means for performing the cutting operation at thelocation ofthe defect indicating means in these boards in which the upgraded board is not er a standard length once the defective section is removed By such a cutting operation.

The further object of this invention is to provide means for performing the cutting operation at a set maximum standard length when no detective sections are indicated.

A still further object of this invention is to provide a cutting apparatus with a control system which will operate in three modes automatically; namely:

(1) to cut defects from boards in one cutting operation, leaving a standard size upgraded board; f

(2) to out defects from boards where indicated, leaving a smaller than standard length board; and

(3) to cut clear boards automatically at a maximum length.

In the practice of the present invention, each degrading defect in the lumber is marked by a defect indicator at the location of the saw cut closest to the defect, which will remove the clear lumber from the defect if the saw cuts there and thenthe lumber is fed endwise to an indicator sensing defect cutter. tector or sensing means is operatively connected to the controls for the board stationary support means and the saw-actuating means.

The detector-means are aligned in two units, which are displaced one from another a distance longitudinal with the path of the boards, which are conveyed past a saw, which when actuated cuts transversely across the boards. On either or both sides of the plane of the saw are placed stationary board supports. Beyond the plane of the saw in a direction remote from the detector means are lengthsensing means, which are also operatively connected to the controls for the board stationary support means and the saw-actuating means. p

With this apparatus the grader places an indicating means at or near the detectivesections of the board, as the boards are conveyed past the plane of the saw, and the sensing means detect the defect-indicating means and through controls actuate the stationary board supporting means which hold the boards in a stationary condition for the period necessary for the saw to be actuated and make a cut at the desired point on the board to trim away the defective section. Once the cutting operation The indicator-de- 3,183,956 Patented May 18, 1965 has been performed the board supports are released and the boards continue to be conveyed. When short lengths of lumber are graded and passed through the apparatus it operates in the same manner as was disclosed in the aforementionedlpaten t. When longer lengths of lumber are conveyed throilgh the apparatus, the first sensing means detects the defectaindicating means and conditions the control means so that if any of the length-sensing means is next actuated before the indicating means is detected by the second sensing means, the saw supports will be actuated, the board will be stopped, the cutting operation will take place, and the remaining clear upgraded lumber will be of a standard size as indicated by "the particular length-sensing means actuated. If, however, the boards are clear, such that they contain no defects for a substantial portion of the board, the first and second sensing means will not become actuated and the boards will pass beyond the plane of the saw until the leading edge of the board actuates a maximum length sensing means which will cause the board supports to stop the boards motion and actuate the saw to :cut the clear board into a standard maximum length. Thus it is seen that with this apparatus it is possible to cut clear lumber at standard length sizes at the same time and with the same apparatus and control means as is used to cut away defects from lumber with the resulting upgraded lumber being either in standard lengths, or if too short for standard lengths, in shorter lengths.

The apparatus for performing the above disclosed operations is substantially the same as that shown in the aforementioned patent, with the addition of length-sensing means, one additional set of defect indicator-sensing means, and a conditional section of electronic controls for the control means. These and other features, objects advantages of the invention will become more fully evident from the following description thereof by reference to the accompanying drawing. Various changes may be made, however, in the construction and arrangement of parts in the machine and eertain features may be used without the use of other features. All such modifications are intended to be within the scope of the appended claims.

The figure is a schematic diagram of the electrical control apparatus associated with the defect indicator sensing means and with the saw and board support actuatred, bearing the defect indicator locating means, comprises infeed and delivery conveyors and other supporting and auxiliary equipment well known in the lumber handling arts such as the system shown in the aforementioned patent. The boards 1 havinga leading edge 2 and may contain a degrading detect 3, which is located and indicated by first'defect indicator means 4 and second defect indicator means 5, all conveyed past first defect iridicator means detecting means 3 and second'defectindicator means detecting means 9. The specific type of defect indicator means usedin this apparatus is not material and it can be any means which can be located or applied by a grader and can be later sensed in the defect cutter apparatus. For purposes of explaining the operation of this embodiment, it can be considered that the indicator means could be made by a graphite pencil or other suitable means producing surface electrical conductivity on the board 1. Preferably these

marks

4 and 5 are applied as lines locating the degrading detect 3. The detector means 8 and 9 can be any suitable means for detecting indicator means and are not limited to electrical conducting indicator means. However, in the embodiment shown in the aforementioned patent, the indicating

means

8 and 9 are comprised of electrical pickup units comprising two sets of interspaced contact elements which slidably engage the top surface of the board 1. These elements are designated 11 and are individually spaced and electrically insulated from the element on either side, such that every other element is electrically connected. The detector means 8 and 9 are mounted in a suitably secure detector mounting means 12.

The saw itself, 14, is mounted on the supporting arm 15 which swings on a fixed horizontal pivot, 16. The saw motor, not shown, is suitably mounted and may run continuously during the operation of the defect cutting apparatus. The saw arm 15 is actuated for cutting when required in a reciprocatory fashion by a suitable mechanical leakage which is actuated by means of a saw actuating cylinder 17 which is in turn controlled by a solenoid valve 18. The boards 1, to be cut as and where required, are fed in sequential manner through the apparatus past the cutting plane of the saw by action of a suitable conveyor means. The feed action of the boards should be of an impositive nature so that the board 1 may be stopped at any instant in order to hold it for cutting. The resting or holding means by which this is accomplished may comprise clamp means 20 which are mounted in spaced locations on either side or, if deisred, on just one side of the saw plane. The holding means 20 is actuated by means of a clamp cylinder 21 which is controlled by a solenoid valve 22.

Near the exit of the cutting apparatus are positioned standard length detecting switches 25, 26, and 27 and a maximum length cutting switch 29. These switches are positioned a fixed distance from the plane of the saw 14 at desired increments in order that the board length can be of standard sizes when cut. For example, it is possible to install sufficient length sensing switches to permit cutting of as many standard lengths of board as may be desired at whatever increment or step of standard lengths which may be practical. As shown, switch 25 is a standard distance of 6 feet 3 inches from the plane of the cutting saw 14. Switch 26 is at a standard distance of 6 feet 6 inches, and switch 27 is at a standard distance of 6 feet 9 inches, with the maximum length switch 29 set 7 feet inches from the plane of the saw. Obviously these length switches could be placed at any distance from the plane of hte saw at any increment between the switches.

Before describing the electronic controls for the defect trim saw a few general remarks concerning the control functions should be made for easier understanding of the individual components making up the control system.

As described in the aforementioned patent, the detector sensing elements when a defect indicator is sensed completes a circuit through the individual sensing elements causing the ionization of a gas filled tube which in turn energizes a relay which actuat-es the clamping means for stopping the movement of the board and the saw actuating means for a cutting operation. This basic control is still used in this invention herein disclosed with the addition of another gas filled tube which is energized by the detection of a defect indicator. through another indicatorsensing means. This first indicator-sensing means once an indicator is detected energizes a gas filled tube which in turn energizes a relay conditioning the saw and clamp control section of the control circuit. If, during this condition period the leading edge of the board strikes or otherwise actuates a length sensing switch this condition completes the necessary connections for ionization of the saw control gas tube and energization of the saw and clamp control relay to cause a sawing operation at that instant. If, however, the leading edge of the board does not strike a length sensing element after the first indicator sensing means has sensed a defect indicator, the defect indicator will pass between the contacts of the second defect indicator sensing means, which will energize the saw and clamp control relay and the cutting operation will be performed. In the third situation of operation wherein no defects are indicated for a substantial length of the board being conveyed past the first and second indicator sensing means, the leading edge of the board will actuate the maximum length sensing switch, which will instantaneously cause the energization of the saw and clamp control relay and result in a sawing operation.

In more detail, the saw control means 40 has the first and second alternating current power terminals 42 and 43 which supply suflicient operating power to direct current power supply 46. The D.C. power supply 46 has several terminals for providing sutficient voltage conditions to operate the various subcomponents of the control system. These terminals are denoted as direct current positive terminals 47, 48, and 49. Also included in the DC. power supply 46 are D.C. ground terminal 50 and DC. negative or bias terminal 51.

The first subcomponent is standard length control thyratron tube 53 which when ionized controls standard length control relay 54 by means of energizing standard length control relay coil 55. The second major subcomponent of the control system is the saw control thyratron tube 73, which when ionized controls the saw control relay 84- by means of energizing the saw control relay coil 85.

In greater detail, from the DC. positive terminal 49 a positive voltage lead 59 conveys current through resistor R-l up to the first defect indicator means detector means 8 to the first defect indicator means detector leads 69 which, upon contact through first defect indicator means a completes the circuit through first defect indicator detector leads '79 through resistor R2 to the standard length control thyratron control grid 89.

Standard length control thyratron 53 has provided cathode 81 and shield grid 91 which are provided with positive direct current from DC. terminal 51 through bias voltage lead 61 connected at junction 71 through resistor R-4. When the circuit is not complete through the detector 8 the control thyratron grid 89 is maintained in a negative bias in relation to the cathode 81 by means of the circuit through resistor R3 to junction 99 with ground lead 60, which is connected at the DC. power supply 46 to DC. ground terminal 50. The standard length control thyratron 53, however, becomes ionized when contact is made from leads as through 79 at the first defect indicator means detector means 8, which places a positive charge on the standard length control thyratron grid 89 in relation to the charge of the standard length control thyratron cathode 81 ionizing the standard length control tube 53 and the current passes from the cathode 81 to the standard length control thyratron anode ltli through standard length control anode lead 111 to the standard length control relay coil terminal 121, which is located in the standard length control relay 54 and causes the energization of the standard length control relay coil 55 when the circuit from the standard length control relay coil terminal 131 is completed through relay coil lead 141, junction 151 and through saw extended switch lead 161, to normally closed switch 63, making contact with positive voltage lead 58 which, in turn is connected with the DC. positive terminal Basically, since the standard length control thyratron 53 is gas filled it remains ionized even though the circuit through the defect-indicating means detector means 8 is broken and there is no longer contact between the first defect-indicator means detector lead 69 and 79.

It is noted that mounted upon saw arm 15 is saw extended switch actuator 77, which makes contact with saw extended normally closed switch 63 when the saw arm 15 has been extended by the completion of the saw cut through the board 1. When the saw extended normally closed switch 63 is contacted by the saw extended switch actuator 77, it becomes open and the standard length control relay coil 55 is no longer energized and the standard length control thyratron 53 becomes deionized.

Actuation of the saw is dependent upon the ionization of the saw control thyratron 73, which occurs in the following manner. The bias voltage is maintained for the saw control thyratron 73, by means of the bias lead 61, which is connected at one end to the DC. power bias voltage terminal 51 through junction 71 to resistor R-S to the saw control thyratron cathode 171 and shield grid 181. When ionized the circuit through the saw control thyratron 73 is completed from the cathode 171 to the saw control thyratron anode 74 through saw control anode lead 75 to saw control relay coil terminal 82, which energizes the saw control relay coil 85 when the circuit through the saw control relay terminal 83 is completed through the relay coil junction 151 through saw extended switch lead 161 and normally closed saw extended switch 63 back through voltage lead 58 to the DC. terminal 48.

When saw control relay coil 85 is energized the saw control relay switch arm 92 is attracted or switched from the right hand position shown in FIGURE 1 to a position to the left. In the energized position the saw control relay switch 93, which normally is in contact with the saw control relay blank contact 103 makes contact with saw actuator contact 113. Likewise, as saw control relay switch arm 92 is pulled from the right to the left position relay switch arm 94 moves from contact with saw control relay blank contact 104 to clamp actuator contact 144, which completes the circuit through junction 154 to the clamp actuator control terminal 164m the solenoid valve 22 for the clamp cylinder 21. The third and final switch arm 95 shifts from relay contact 65 to relay ground contact 105, which completes the circuit through ground junction 115 to ground lead 60 to the junction point 139 and finally to ground 149.

In operation saw control relay 84 in the condition caused by the energization of saw control relay coil 85 completes the circuit through saw actuator contact 113 to the solenoid valve 18 for the saw cylinder 17 through the saw actuator lead 123, which through junction 133 completes the circuit through the second alternating current power junction 143. Once the solenoid valve 18 has become energized the actuated cylinder 17 begins the reciprocal movement of the saw arm 15 to bring the saw 14 through the board 1. At the same time the circuit through the clamp control lead 144 is completed to the solenoid valve 22 for operating the clamp cylinder 21 which positions the clamp 20 to hold the board 1 in a stationary position during the sawing operating. The circuit to the solenoid valve 22 is completed through the clamp actuator control terminal 174 through junction 133 to the second alternating current power junction 143. The relay switch arms 93 and 94 which have completed this clamp and saw circuit are commonly joined at junction 114 through junction 124 to the first alternating current power junction 134, thus providing the completed circuit for the actuation of the solenoid valves 18 and 22.

Saw actuated switch actuator 78 is mounted on the saw arm 15 in order that when the saw 14 is reciprocated the normally closed saw actuated switch 68 is permitted to close, makingcontact between the junction 154 and the junction 124, which in elfect by-passes the relay supply 114 and 144 for completing the circuit to the

A.C. power terminals

134 and 143, thus the solenoid 22 for the operation of the clamp cylinder is energized even though the relay contact 94-may break contact from the clamp control lead 144 when the saw control relay coil 85 is de-energized. In this regard, it should be noted that the solenoid valve 18 has no by-pass connections around the saw control relay 84, thus when the saw control relay coil 35 is no longer energized, saw control relay switch arm 93 reverts to the right hand position, breaking contact between the switch arm 93 and the saw actuator contact 113 and de-energizes the solenoid valve 18 allowing the saw arm 15 to reciprocate back to the unactuated or normal position.

Since the saw control relay coil 85 is not energized unless the thyratron saw control tube 73 is ionized, it is now necessary to discuss the various conditions which Will cause the ionization of thyratron 73. The simplest condition which will ionize thyratron 73 occurs when the second defect indicator detecting means 9 senses a defect indicator means making contact between the second defect indicator control leads 109 and 119 completing the circuit through nesistor R-6 to the saw control thyratron control grid junction 129.

The second condition which will cause the ionization of thyratron 73 exists when the leading edge 2 of the board 1 makes contact with the maximum length switch 29. The maximum length indicating switch 29 is normally connected through lead 67 and resistor R-S to high voltage lead 57 and in turn to direct current terminal 47 of the direct current power supply 46. This connection includes the circuit to the lower side of the capacitor 319 where the higher side of capacitor 319 is connected through

junction

309, 307, 306, and 305 to length sensing ground 300 which in turn makes contact at junction 115 with saw relay control ground contact 105. Thus, in the normal position, capacitor 319 is charged and when the leading edge 2 of the board 1 contacts the maximum length switch 29 the switch 29 breaks from the contact with lead 67 and makes contact with maximum length lead 339 and ultimately to saw control relay switch arm 95 which is the normal condition is in the right hand position contacting maximum length relay contact 65 which through junction 66 completes the circuit to the thyratron 73 control grid 129. Thus, in the normal position of the saw control relay 34 the discharge of the maximum length switch capacitor 319 causes the ionization of the thyratron 73 and thus cuts the board 1 at the maximum length.

The third and final condition which causes the ionization of the saw control thyratron 73 results in the sequential operation of one of the standard length switches 25, 2,6, or 27 after the ionization of standard length thyratron 53. The standard length switches 25, 26, and 27 are connected in a similar manner as is maximum length switch 29 to the high voltage terminal 47 of the DC. power supply 46 by means of leads 57 and 67 and this places a strong positive charge on the lower side of the standard length capacitors 315, 316, and 317, respectively, which are, on the higher side, connected with length sensing ground 300 at

junctions

305, 306, and 307. However, and in distinction from the circuit of the maximum length switch 29, the standard length switches 25, 26, and 27 when actuated make contact with a different circuit than that made by the actuation of the maximum length switch 29. When actuated the standard length switches 25, 26, and 27 make contact with standard length leads 335, 336, and 337, respectively, which through resistances R9, R10, and R-11 make contact with standard length control relay lead 364 which is in series with the standard length relay contact arm 64 in standard length relay 54. In the normal condition of the standard length control relay 54, the relay contact arm 64 is in the right hand position making contact through standard length relay ground contact 70 to the ground lead at ground junction 80. Thus, when contact is broken at the standard length switches by the actuation of the standard length switches caused by the leading edge 2 of the board 1, the capacitors 315, 316, and 317 discharge through to ground and cause no other actuation or operation of the cutotf saw 14. However, if the first defect indicator means detecting means 8 has detected a

defect indicator

4 or 5 completing the circuit through detector leads 69 and 7 0 causing the ionization of the standard length thyratron tube 53 and the resulting energization of the standard length control relay coil 55, the relay contact arm 64 is pulled from the right t0 the left position now making contact with relay contact which through junction 66 completing the circuit through the saw control thyratron grid 129. Thus, after the energization of the standard 7 length thyratron tube 53 and during the energization of the standard length relay control coil 55, if any one of the standard length detector switches is caused to make contact discharging the standard length capacitors 315, 316, or 317, this discharge current will be carried through the standard length relay 54 and ionize the saw control thyratron 73.

It should be noted that since it is anticipated that the standardlength and maximum length detector switches 25, 26, 27 and 29 will be positioned somewhat remote from the control tubes that transient current surges could possibly result in premature ionization of the saw control thyratron 73. To prevent such transients from interfering with the correct operation the standard length leads are shielded and these shields have ground connection 34% which in turn make contact with standard length lea shielding ground 350. 7

Operation Having described with particular detail the specific operation of the various subcomponents of the defect trim saw and its controls, the operation of the apparatus in the three modes will now be disclosed.

The first of the three modes is that incurred when the boards which are to be trimmed of defects are of relatively clear lumber having defects occurring periodically in their over-all length. The second mode of operation is involved in the trimming of lumber which has several defects throughout its length with small clear sections interspersed between the defective sections. The third mode of operation is that incurred for lumber which has very few defects and is substantially clear from end to end.

In reference to the first mode of operation the board 1 is conveyed to the defect trim saw table after it has been graded and the defective sections have been indicated by a detectable means by the grader. As the board passes the first and second defect indicator means detecting

means

8 and 9 nothing happens until a defect indicator means such as 4 or 5 has been sensed. With large clear sections passing below the detecting

means

8 and 9 the saw 14 is not operated. The leading edge 2 may strike the standard length switches 25, 26, and 27 and if this occurs before a defect indicator is detected by first defect indicator means detecting means 8 nothing will happen. In such situations the standard length switch contact will break contact with the length switch contact 67 and make contact with standard length lead 335, discharging the capacitor 315 through to ground with no change in the operation of the machine. When a defect is sensed by detecting means 8 the standard length control thyratron 53 becomes ionized energizing the standard length control relay 54, switching the relay contact arm 6 to make contact with relay contact 65 and if after this has occurred but before the defect passes to be detected by the second defect detecting means 9 the leading edge 2 strikes another standard length switch such as 26 the capacitor 31d will discharge through the standard length control relay. lead 364 and will cause the ionization of the saw control thyratron 73 energizing the saw control relay 84 which will actuate the solenoid valve for the clamp cylinder 22 which positions the clamp 29 to stop the board 1 at the same time the solenoid valve 18 for the saw cylinder 17 is energized causing the reciprocal movement of the saw arm 15 cutting the board 1 separating a standard length of clear board from the degrading defective'section 3. Whenthe saw 14 returns from the cutting stroke with the relays tie-energized due to the break in the saw extended normally closed switch 63, the clamps 2t) will be released when the switch 68 opens and the conveying will continue.

The second mode of operation may occur shortly after the first mode or" operation in that the detecting means 8 will detect the second defect indicator means 5 and since ,thenew leading'edge, which occurs at the sawed ofi point from the fi st mode of operation, will not strikea standard length switch 25, as, or 27 before the defect indicator means 5 is sensed by the second defect indicator means detecting means 9. When the second defect detecting means 9 senses the detect'indicator means 5 the saw control thyratron 73 is again ionized, energizing the saw control relay 84 for another cutting operation of the saw 14.

The third mode of operation occurs when the board 1 is clear for significant length such that as it passes the defect indicator means detecting

means

8 and 9 there are no defect indicator means sensed and the leading edge 2 of the board 1 passes all of the standard length switches and finally causes the actuation of maximum length switch 29. This actuation causes the discharge of the capacitor 319 through the lead 339, making the circuit through the saw control 84 to the relay contact arm 5 which is in the normal right hand position making contact with the lead 65 which through junction 64 causes the ionization of the saw control thyratron 73. Once ionized the saw control thyratron 73 energizes the saw control relay 84 for a cycling of the saw 14 for a cutting operation resulting in a standard maximum length of clear lumber.

Having now described my invention and in what manner the same may be used, what I claim as new and desire to protect by Letters Patent is:

l. A lumber-cutting apparatus comprising:

a conveyor means for conveying boards endwise to and from a cutting station,

a transversely reciprocative cut-01f saw being actuatable for a cutting operation for cutting said boards at said cutting station,

means for holding said boards during said cutting operation,

a first set of defect indicator means detector means positioned in the path of said boards before said boards reach the plane of said saw,

, a second set of defect indicator means detector means positioned in the path of said boards between said first set of detector means and said plane of said saw,

a length detecting means positioned in the path of said boards at a distance from said plane of said saw remote from said first and said second detector means,

control means for actuating said saw responsive to conditions indicated by said first and second detector means and said length detecting means.

2. The lumber-cutting apparatus of claim 1 wherein:

said length detecting means includes a maximum length detecting means,

said control means actuates said saw responsive to the actuation of said maximum length detecting means.

3; The lumber-cutting apparatus of claim 1 wherein:

said length detecting means includes standard length detecting means, and

said control means actuates said saw responsive to the actuation of said standard length detecting means after the actuation of said first detector means but before the actuation of said second detector means.

4. The lumber-cutting apparatus of claim 1 wherein:

said control means actuates said saw repsonsive to the actuation of said second detector means.

5. A lumber-cutting apparatus comprising:

a conveyor means for conveying boards endwise to and from a cutting station, g

a transversely reciprocative cut-off saw being actuatable for a cutting operation for cutting said boards at said cutting station,

' means for holding said boards during a cutting operation, a

a second set of defect indicator means detector means positioned in the path of said boards between said first set of detector means and said plane of said saw,

length detecting means positioned in the path of said boards at a distance from said plane of said saw remote from said first and said second detector means, 7

said length detector means including a maximum length detector means and a standard length detector means,

control means actuating said saw responsive to;

1% actuation of said maximum length detector means, actuation of said standard length detecting means after the actuation of said first detector means but before the actuation of said second detector 5 means,

actuation of said second detector means.

No references cited.

10 WILLIAM W. DYER, 111., Primary Examiner.

Claims

5. A LUMBER-CUTTING APPARATUS COMPRISING: A CONVEYOR MEANS FOR CONVEYING BOARDS ENDWISE TO AND FROM A CUTTING STATION, A TRANSVERSELY RECIPROCATIVE CUT-OFF SAW BEING ACTUATABLE FOR A CUTTING OPERATION FOR CUTTING SAID BOARDS AT SAID CUTTING STATION, MEANS FOR HOLDING SAID BOARDS DURING A CUTTING OPERATION, A FIRST SET OF DEFECT INDICATOR MEANS DETECTOR MEANS POSITIONED IN THE PATH OF SAID BOARDS BEFORE SAID BOARDS REACH THE PLANE OF SAID SAW, A SECOND SET OF DEFECT INDICATOR MEANS DETECTOR MEANS POSITIONED IN THE PATH OF SAID BOARDS BETWEEN SAID FIRST SET OF DETECTOR MEANS AND SAID PLANE OF SAID SAW, LENGTH DETECTING MEANS POSITIONED IN THE PATH OF SAID BOARDS AT A DISTANCE FROM SAID PLANE OF SAID SAW REMOTE FROM SAID FIRST AND SAID SECOND DETECTOR MEANS, SAID LENGTH DETECTOR MEANS INCLUDING A MAXIMUM LENGTH DETECTOR MEANS AND A STANDARD LENGTH DETECTOR MEANS, CONTROL MEANS ACTUATING SAID SAW RESPONSIVE TO; ACTUATION OF SAID MAXIMUM LENGTH DETECTOR MEANS, ACTUATION OF SAID STANDARD LENGTH DETECTING MEANS AFTER THE ACTUATION OF SAID FIRST DETECTOR MEANS BUT BEFORE THE ACTUATION OF SAID SECOND DETECTOR MEANS, ACTUATION OF SAID SECOND DETECTOR MEANS.