KNEE POSITION RECORDER FOR SAWMILL CARRIAGE HEADBLOCKS

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1 U. S. DEPARTMENT OF AGRICULTURE FOREST SERVICE FOREST PRODUCTS LABORATORY MADlSON, WIS. In Cooperation with the University of Wisconsin U. S. FOREST SERVICE RESEARCH NOTE FPL-0139 AUGUST 1966 KNEE POSITION RECORDER FOR SAWMILL CARRIAGE HEADBLOCKS

2 Summary A research instrument is described that automatically records the exact amount the knees of sawmill carriage headblocks move in making rapid successive sets during the sawing operation. It was designed for use on the Forest Products Laboratory s conventional sawmill that is used for studies of sawtooth action and saw performance. It is believed to also have application where an automatic and positive record is required of a succession of irregular intermittent indexing actions. The instrument consists of a marking stylus mounted on the side of the sawmill carriage headblock and a batterypowered electric circuit that produces a mark on an electrosensitive tape. The tape is inserted in a holder affixed to the side of the headblock base. Microswitch assemblies activated by stationary cams positioned along the sawmill track serve to control momentary electric impulses that mark the electrosensitive paper.

3 KNEE POSITION RECORDER FOR SAWMILL CARRIAGE HEADBLOCKS By F.B. MALCOLM, Forest and Products L.H. REINEKE Technologists 1 Forest Products Laboratory, Forest Service U.S. Department of Agriculture Introduction Rough green boards have long been used as a guide for evaluating the performance of a sawmill. Mill managers use thickness and width as a base for a form of quality control. In research, studies of mill performance are not only concerned with the dimensional characteristics of boards, but with the tell-tale marks left by the saw in its cutting action as well. In the process of manufacture, the board acquires on its surfaces most of the evidence of the various mechanical factors acting on it: more specifically, the action of the saw and sawteeth, the influence of the carriage movement and carriage parts and, the interaction of these factors. The isolation and precise determination of the influence of each factor is essential for improving the performance of the saw and sawing equipment. Figure 1 depicts many of the characteristics acquired by rough-sawn boards during sawing. Board surface degradation (surface roughness), caused by sawtooth action, and variations in board thicknesses are interrelated with the required depth of planing and the actual set thickness of the board. These factors are further interrelated with successive boards sawed. With a precisely engineered and constructed research sawmill the controlled movement of the carriage headblock knees and the actual set performed by the setworks (the measured advance of the cant or log on the carriage toward the sawline) present no problem. However, on the conventional production-type mill 1 Maintained at Madison, Wis., in cooperation with the University of Wisconsin.

4 the amount of metered movement of the knees or the set performed by the setworks (actual set) and the amount of movement or set intended (theoretical set) may vary considerably. Setworks Deficiencies Setworks may fail to provide the desired uniform successive sets because of slack or play in its various parts, irregular spacing of the teeth of the setworks ratchet wheel, slippage of the setworks pawls, failure to make a complete throw of the setworks lever, set-shaft torsion, or headblock knee reaction to forces exerted by the log as stresses in it are released in sawing. Thus, the theoretical set seldom will be the same as the actual set. Obviously setworks inaccuracies cannot be isolated directly from the board measurements. For normal commercial operations, certain thickness variations are tolerated, established by methods of quality control. However, in saw performance studies a method for determining the precise set thickness is necessary. Such a method was developed at the Forest Products Laboratory. Effect of Setworks Deficiencies in Research Studies The setworks on the sawmill carriage at the Forest Products Laboratory is a conventional, manually operated, double acting type. The sawmill is used for utility and research purposes. Despite full use of the adjustments provided, variation in setting still occurs and may be as much as 3/32 inch when making rapid consecutive settings in sawing a log or cant. This setting tolerance may be acceptable for commercial sawing, but it can completely mask factors involved in saw performance studies. If the theoretical set is used as the basis from which measurements of saw cutting action are made, any error in the actual set automatically is attributed to other factors. An example of this is illustrated in the measurements on one of a series of boards produced during a saw performance study. The maximum calipered thickness of the rough board was 1-1/8 inches, the theoretical set thickness as indicated by the setworks was 1 inch even. Part of the data required was concerned with surface degradation below the set thickness. The final thickness of the board after planing to remove the evidence of sawing action was 15/16 inch. Thus, the total planing requirement to remove thickness variation and surface roughness from both sides was 3/16 inch. The actual thickness FPL

5 accomplished by the setworks, however, was 1-1/16 inch. If surface roughness were applied to the theoretical set thickness, the data would show that apparently only 1/16 inch of planing would be required. However, the actual set performed by the setworks was 1/16 inch more than the theoretical set, thus 2/16 inch of planing below the actual set thickness was required. Obviously the use of the theoretical thickness would mask some of the effect of saw behavior and sawtooth action. It is evident, therefore, that when precise data are required, a means of positively recording the exact set made by the setworks is needed. FPL Setworks Set Recorder An instrument to measure the actual set of the Laboratory s sawmill is described in this report. It is believed to have value not only for those engaged in sawmilling research but also has application where an automatic and positive record is required of a succession of irregular intermittent indexing actions, Operation The basic function of the device (fig. 2) is to register precisely the position of the knee relative to a starting point on the bolster, at two predetermined stages in each sawing-gigback cycle. Knee position is registered as a very fine dot on electrosensitive paper that is attached to the bolster. The dot is produced by an electric current passing through a fine wire stylus mounted on a carrier that is attached to the knee. The carrier moves with the knee and slides the styli along the recording paper. Two styli are provided, one for each stage. The current pulse for marking occurs when a switch on the carriage is momentarily closed either manually (to mark the starting position through both styli) or automatically by a separate switch-activating cam for each stylus, located at appropriate points along the trackway. Current is provided by a dry battery mounted on the carriage. A schematic diagram of the electric circuit is shown in figure 3. Because of its use for research purposes, each of the five headblocks of the Laboratory mill is equipped with a complete recording assembly connected in parallel with the main circuit. Components and Function The various components of the electric circuit are as follows: (1) The 90-volt dry battery power supply is controlled with an on-off switch in the main bus line (positive) (fig. 4). A 2,000-ohm, 5-watt rheostat (optional) may be installed immediately after the on-off switch to adjust voltage for best results (fig. 3). FPL

6 (2) A double-pole single-throw momentary switch, normally open, connects the main bus to both secondary buses when closed manually (figs. 3 and 4). (3) A normally open microswitch (fig. 3,As) with roller actuator, connects the main bus to secondary bus (Ab) when an under-the-carriage lever is moved by a cam on the trackway as the carriage moves forward (figs. 2 and 3). (4) A similar microswitch (Bs), at another point under the carriage connects the main bus to secondary bus (Bb) when its lever is moved by a second cam on the trackway during the carriage travel. (5) A ground wire is necessary on wood-frame carriages. The negative battery terminal and the base or bolster of each headblock are connected to this ground wire, which may be bare (fig. 5). The setshaft should not be used as a ground because the lubricant at each bearing prevents completing the circuit. With metal-frame carriages on which the bolsters are in direct metal-do-metal (paint-free) contact with the frame, the negative terminal of the battery may be connected to the frame, hence no ground wire is needed. (6) At each headblock, a branch line incorporating a 1,000-ohm, 1/4-watt current-limiting resistor runs from each secondary bus to a polarized Jones receptacle (two-pin female chassis-type) installed in the side of the bolster near its rear end (fig. 2). All branch lines from one secondary bus should run to the narrow contact of its receptacle, and those from the other secondary bus should run to the wide contact for uniform location of feed and gigback traces (fig. 3). (7) Two of the wires of the coiled telephone cord are attached to the mating Jones plug (fig. 2) and the other ends to the two styli mounted on a bracket of the stylus carrier assembly (fig. 6) attached to the knee. This bracket places the styli in contact with the recording paper strip (fig. 7). (8) A holder for the recording paper strip is located on the side of each bolster, parallel with and near its top (figs. 6 and 7). This holder is of thin stainless steel with about 3/16 inch of each edge bent through 180 to form a channel in which a 35-millimeter-wide strip will slide freely but without excess side play. The paper strip is anchored in the holder at each end by a slightly curved flat spring clip, inserted between the paper and the channel lip (fig. 7). This holder is attached to the side of the bolster with countersunk flat-head machine screws located below the centerline. The upper half thus forms an operating zone for the styli that is free of depressions or bumps. When the side of the bolster is not machined, the paper holder is fastened to a flat surface parallel with the travel of the knee, using a 1/8- by 1-1/2-inch cold-rolled steel base fastened with suitable shimming to the bolster to form a straight support. (9) The marking switch assembly consists of a normally open (N.O.) microswitch actuated by the upper end of a wood lever when its lower end encounters a cam on the trackway (fig. 8). The pivot bolt for the lever is mounted in a wood bracket attached to the underside of the carriage (fig. 2). The lever has a bushing for free turning on the bolt pivot. This bushing is sliglitly longer than the thickness FPL

7 of the lever to prevent binding. A music wire spring is inserted in the edge of the lever and extends through a screw eye attached to the wood bracket to return the lever to a vertical position after each operation. (10) A right-angle bracket (cold-rolled steel), independently fastened to the trackway, serves as a cam to pivot the lever enough to momentarily activate the switch (fig. 8) as the carriage moves. The switch is activated only in one direction of carriage movement. The steel cams can be placed at any desired point along the track to suit the length of the logs and their placement on various headblock combinations. The microswitch assembly connected to one stylus is offset from that of the assembly connected to the second stylus so that the respective cams are in adjacent lanes. Operational Procedure The procedure used on the Laboratory mill for recording knee set-position when making a saw performance study first involved preparation of a cant of the desired size. All sawing to produce the cant from a log was done immediately before making the saw lines for the study. Two opposite faces were sawed to establish cant thickness; the third (adjacent) face was then sawed and turned to the knees and the cant securely dogged. Before setting for the slab cut on the fourth face, the cams for the knee position recorder were positioned. The cam in the first lane was placed so that microswitch As would close immediately before the saw engaged the cant (thus producing a mark on the paper) and the cam in the adjacent lane was placed so that switch Bs closed shortly after the rear of the cant left the front of the saw (likewise producing a mark on the paper). The total setting run was then calculated which included the thickness of the several sets required in the series of saw lines plus the required thickness of the dog board. The electrosensitive paper was placed in the holder and secured tautly with a metal clip at each end. The setworks was then activated to move the knees a short distance to take up any slack that might have resulted from turning and dogging. After closing the battery switch, the momentary switch was pressed to mark the initial position of both styli. This mark served as a reference point from which all measurements of succeeding dot positions were measured. The setworks then advanced the knees for the slab cut to the calculated setrun as indicated on the setworks dial. The predetermined series of saw cuts were made without stopping between cuts, as would be done in normal sawing. The recording strip was then removed. This sequence was followed for each cant studied. FPL

8 The cumulative distances from the initial mark for each stylus to the respective mark for each successive cut were measured to the nearest 0.01 inch as soon as practical after sawing was completed. These differences between successive distances on the presawing stylus line (fig. 7) were the actual knee advances or sets produced by the setworks. Any difference between these cumulative distances and the corresponding ones on the postsawing line is the measure of knee shift during the relevant sawcut. Certain features of the operation of the knee position recorder should be carefully noted. (1) The electrosensitive paper has an electrically resistant coating that requires an electric potential of 65 volts or more to make distinct marks in the circuit described. The required potential will change if resistors of other values are used. (2) Relatively fresh batteries should be used to insure distinct marks. Used or out-dated batteries should be checked for output. (3) Connections to the screw post terminals on the stylus carrier should be made carefully to avoid grounding or shorting. (4) The height of the cams should be sufficient to move the lever into but not beyond the switch-closing position. Cam and lever ends should be smooth and shaped to prevent jamming if the carriage movement is reversed when the lever is still in contact with the cam. Other Applications In addition to establishing the actual set, the knee position recorder was also used to detect differences in advance of individual knees. In this way it was found that appreciable torsional spring could develop in the set shaft, depending on the distance from the setworks and the pressure exerted on the headblock from the weight of the log or cant, and the action of heavy dogging to secure it. On the Laboratory mill the differential in set between the knee nearest the setworks drive and the knee at the far end of the set shaft amounted to 5/64 inch. This resulted from the reduced friction between cant and bolster (base) as successive cuts reduced the weight and contact area. The differential in set dropped stepwise- in two steps--rather than gradually, causing thickness variation before the dog board was reached. These variables need to be determined and taken into account when making sawmilling and saw performance studies. The device described here can help to isolate these equipment variables by determining the actual amount of movement of each headblock knee. It has further possibilities in measuring the interaction of equipment and material when appreciable spring in the log may distort the carriage or pull a knee forward in a reversal of the normal take-up of loose-play in setting. FPL

9 Figure I.--Sketch iilustrating many of the characteristics acquired by rough-sawn boards during sawing. M Legend T = Maximum MX-l of board measured No. I thickness T MN-I = Minimum of board measured No. 1 thickness T MX-2 = Maximum of board measured No. 2 thickness T = Minimum measured MN-2 of board No. 2 thickness K W = Sawtooth kerf width K = Residual kerf clinging to B board surface S D = Surface degradation E T = Edge tear-out P S-I = Planing depth, Ist face P S-2 = Planing depth, 2nd face P = Final TH of all planed thickness free sawing marks A S-I = Actual board A S-2 = Actual board set No. I set No. 2 thickness, thickness, S = Theoretical set for TH board thickness

10 Figure 2.--Knee position recorder installation showing various assemblies in place: sliding stylus with cord and connecting Jones plug (center and left arrows); electrosensitive paper in holder attached to side of headblock base; microswitch, wood lever and right angle steel cam (lower left arrows).

11 M Figure 3.--Circult diagram for knee position recorder.

12 M Figure 4.--Battery and battery box unit showing switch positions; (A). on-off switch, (B) manually operated momentary switch. M Figure 5.--Stylus-carrier assembly and paper holder with electrosensitive paper In place. The grounding wire (A) is attached to the headblock near the connecting plug.

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14 M Figure 7.--Arrow indicates characteristic marks on electrosensitive paper that register the actual knee position for each cut. One stylus marks the knee position as the saw enters the cut, and the second stylus marks the position after the cut is made. M Figure 8.--DetaiIs of marking switch assembly.

15 PUBLICATION LISTS ISSUED BY THE FOREST PRODUCTS LABORATORY The following lists of publications deal with investigative projects of the Forest Products Laboratory or relate to special interest groups and are available upon request: Architects, Builders, Engineers, and Retail Lumbermen Box, Crate, and Packaging Data Chemistry of Wood Drying of Wood Fire Protection Fungus and Insect Defects in Forest Products Furniture Manufacturers, Woodworkers, and Teachers of Woodshop Practice Glue and Plywood Growth, Structure, and Identification of Wood Logging, Milling, and Utilization of Timber Products Mechanical Properties of Timber Structural Sandwich, Plastic Laminates, and Wood-Base Components Thermal Properties of Wood Wood Fiber Products Wood Finishing Subjects Wood Preservation Note: Since Forest Products Laboratory publications are so varied in subject matter, no single catalog of titles is issued. Instead, a listing is made for each area of Laboratory research. Twice a year, January 1 and July 1, a list is compiled showing new reports for the previous 6 months. This is the only item sent regularly to the Laboratory s mailing roster, and it serves to keep current the various subject matter listings. Names may be added to the mailing roster upon request.