A RAPID METHOD CF DETERMINING THE SPECIFIC GRAVITY CF VENEER May 1943 m « f war imm man « m U.S DtP« ; This Report is One of a Series Issued In Cooperation with the ARMT-NAVT-CIVIl COMMITTEE on AIRCRAFT DESIGN CRITERIA Under the Supervision off the AERONAUTICAL BOARD No. 1397 UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE FOREST PRODUCTS LABORATORY Madison, Wisconsin In Cooperation with the University of Wisconsin A EAPID METHOD 0? DETEHMINIZTG THE SPECIFIC GRAVITY OF VENEER^ B3 BENSON H. PAUL, Senior Silviculturist and JOHN P. LIMBACH, Assistant Forest Products Technologist Summary A rapid method of determining the specific gravity of veneer has been developed. A sample of veneer is acurately cut with an ordinary paper trim- mer to 100 square centimeters - (10.0 by 10.0 centimeters) or 50 square centi- meters (7.07 by 7.07 centimeters) depending upon its thickness. The thick- ness of the veneer is measured by a micrometer to 0.001 of an inch. The veneer is then attached to a sensitive spring of the type used in a Jolly balance, and a chart is read directly in specific gravity for the given thickness of veneer employed. Parallel readings for allowable tolerances of thickness are included. The specific gravity of the sample at the current 3 moisture content— is read directly from the chart. If the veneer is oven dry, the specific gravity will thus be read directly from the chart. For veneer at a moisture content below the fiber-saturation point, a simple con- version from ci^rrent specific gravity to an oven-dry weight and oven-dry volume basis may be made by subtracting the product of a constant and the percent of moisture. Such constants for each species and for groups of species are given. Equipment and Use The equipment required consists of: 1. A paper trimmer with adjustable stop to cut the veneer samples to size. The trimmer is modified as shewn by providing a guide and a piece of sandpaper glued to the trimmer surface to hold the veneer firm (fig. l). —This mimeograph is one of a series of progress reports prepared by the Forest Products Laboratory to further the Nation's war effort, Results here reported are preliminary and may be revised as additional data become available. —One inch equals 2.54 centimeters. 3 —Moisture content may be determined according to Army-Navy Specification AN-W-3, or by means of an electrical moisture meter suitable for use with veneer. Mimeo. No. 1397 -1- •rometer caliper to measure veneer thickness (fig. l). 3. A gage consisting of a cteel plate 10 by 7.07 "by 0.16 centimeters, or 3.94 by 2.78 by 0.06 inches (fig. l). The gage is used to set the trimmer stop for cutting samples of either ICC or 50 square centimeters surface area. A rule graduated to 0.C1 inch or to 0.02 centimeters may be used in the ence of a prepared steel plate gage. Cut veneer sample at a r le to the grain using a wood block to hold the veneer flat (fig. 2). 4. A sensitive helical spring, of the type used in a Jolly balance, - ng an elongation of about 5 centimeter per gram within a range of ab< I 9 grams. The spring can be purchased from scientific equipment suppl; - es at a very nominal cost. 5. A strong piece of thread. One end of this thread is tied to the spring, and a paper clip is fastened to the other end, Ine paper clip is used to attach the veneer samples to the thread. The thread carries an indicator which should be checked frequently at zero chart reading. The indicator . re a horizontal line on a small piece of paper fastened to the thread through two holes so that it can be slid up or down. 6. A suitable support from which the spring can be suspended, a. which the specific gravity chart may be fastened. This support may have base with three leveling screws, or the spring and chart may be suspended by m§fins of screw-eyes driven into a wall, in which event the diameter of * screw-eye should be slightly larger than that of the spring. "■./.ere a is not available, the screw-eyes may be driven into a flat board that is I suspended from above. 7. A 5-gram weight, to be used in adjusting the elongation of the Bpring to the specific gravity chart. 6. A specific gravity chart. (This chart, devised b; Products Laboratory, may be detached from this report and mounted for us< . Calibration of the Spr: . Adjust the elongation of the spring to the spec': the correct suspension point of the sprin . . This pc can be found experimentally as follows : I lace the small end of the spr: through the support srew— eye (or other support) and insert a t. 'rip of metal (an old razor blade will serve) over the screw-eye and Lnto a coil near + ne extremity of the spring. ' he paper clip in place, set the zero .0 of the weight scale (shov I side c. specific gravity chart) under the indicator. Fasten the 5-gram weight to the paper clip - note where the indicator falls on the weight scale. If the indicator is - .-ied past the 5-gram mark, remove the 5-gram we: .d shorten the ef- fective length of the spring by Intercepting it farther doi itr . -^set the indicator on zero and again note the displace tit, Repeat this procedure until the weight displaces the 0. .'0. 1397 spring just the right amount to bring the indicator from the zero point to the 5- gram line. It is a good plan to insure against the spring being overloaded by placing a smaller screw-eye under the spring at the point beyond which it should not be stretched. If the suspension thread is then passed through this screw-eve, the spring will not be elongated beyond this point. Procedure to Find Specific C-ravity of Veneer 1. Set the paper-trimmer stop with the steel plate gage (fig. l) and cut the veneer sample to size (fig. 2). (Samples will have a square surface. Use 100-square-centimeter samples for veneers of average density and of thin to medium thickness; use 50-square-centimeter samples for very heavy woods or thick veneers. This precaution is taken to prevent overloading of the helical spring. ) 2. Obtain the average thickness of the sample with the micrometer, select the proper thickness line on the specific gravity chart, and adjust the chart so that the selected line is back of the vertical thread. 3. Adjust the zero line of the chart to the indicator on the thread. 4. Attach the veneer sample to the paper clip on the thread and read, the specific gravity as registered by the indicator on the thread (fig. 4). ('■'"hen the sample is 50 square centimeters in surface area, the specific gravity reading will have to be multiplied by 2.) If the sample is oven dry, the specific gravity of a 100-square-centimeter sample is thus obtained with- out computation. 5* If the sample is not oven dry, correct the specific gravity from current volume and moisture eontent below fiber saturation point to an oven- dry weight and oven-dry volume basis by use of the following: Specific gravity equals chart reading at X-percent moisture content minus KX, where K is a constant for each change of 1 percent in moisture content for a given species. Aircraft woods listed in Army-iTavy Aeronautical Specification Plywood, and Veneer, Ko. AIT- 1T1T-P- 511b, have the following values of E: Mineo. To. 1397 Aircraft woods K Alaska "birch, basswood Am .lean beech, paper birch .CC10 Sweet gum . OC American elm, white spruce .C013 Noble fir, sweet birch, yellow birc .C014 Sycamore .0015 gar maple, yellowpoplar .CC16 . ma^le, red spruce, water tupelo ,0018 tka spruce, southern magnolia, black walnut ,0C -ouglas-fir, pecan, silver maple, western hemlock . 020 Ponderosa pine, ^ort Orford white-cedar ,0021 Sugar pine .0022 Eedwood ,001 Khaya (so-called African mahogan; .0027 .ogany (from Tropical America) . 1 21 Tor approximate values the constant may be rounded to the nearest d: in the third decimal place, as 0.CC1, 0.002, and 0.003, Use of Chart for Other Thicknesses of Veneer For veneer in thicknesses of 0.014 to G.021 inch ; Suspend a sample 100 square centimeters in surface area en the line of the chart representing twice its actual thickness, and double the reading to obtain the correct specific gravi I . For veneer in thicknesses of 0.056 to 0.086 inch : Suspend a sample 50 square centimeters in surface area on the line representing half its thickness, and read specii lirectly from the "hart. Inspection Procedure for Bulln terial In some inspections, the or ;1 is to asc< rity of -ood selected decs not fall below a certain poj b, su t is not the actual determination of the specific gravity of each sample that is Bought. In these instances, it is possible *c ■ irten still further the in- spection procedure, as follows: 1, Cut the veneer sample to size. 2. From the specifications determine the maximum to be dealt with in the tolerance range of the veneer samples to be tested. Set I Mimeo. no. ] -4- thickness scale of the specific gravity chart for this thickness back of the thread and note the passing mark (least passing specific gravity mark, cor- rected for moisture content when necessary) on the chart. Assume that all pieces registering an equal or greater value than this are acceptable. The pieces that do not pull the indicator down to the passing mark may be de- ficient in thickness and, after being calipered, they still may be acceptable if they reach the passing ::iark for their particular thickness. This leaves only a fraction of the total number of pieces to be calipered, thus saving- time in inspection. Kimeo. lie. 1397 -5- u © •H u -p o 1 -P 73 •rH T3 g 0) -p a5 C a, W to * as (D to e t. 3 tuJ CD O -P d w CD CD CD -P •H -P +> o OJ CD t, 3 tuD •H ■ 1 * [i: 46949 Fj 4V Figure 3. — Method of calibrating spring. Figure h. — Determining specific gravity of veneer, SCTPFUXHTABT OHUP JOB DanBHIHW 3F10ITI0 OBaTITT OT VMHR applanation of Supplementary Chart Thia supplementary chart Is Intended for use In determining the spe- cif lc gravity of aircraft veneer in thicknesses not covered by the original chart accompanying Tor oat Products Laboratory Himeo. lo. 1397 ■ "* *apid Method of Determining the Specific Gravity of Veneer." The original chart cannot be used directly for veneers ranging in thickness from 0.021 to 0.028 inch, which Includes l/Ug-lnch material; 0.043 to 0.056 inch, which includes 1/20- Inch material; and from 0.086 to 0.1l6 inch, which Includes l/10-lnch stock. This supplementary chart covers those ranges, and may hence be used alternately with the original chart as needed. It is used in the same manner as described in Himeo. 1397 * 0T the original chart, except that samples are cut to either 75 square cantlmetere in surface area (3-410 inohes on a side) or 37.5 square centimeters (2.411 Inches on a side). Table 1 summarises veneer thicknesses, specimen aises, and procedures for use with either chart. Table 1. — Charts and procedures to use In finding specific gravity cf veneer samples of different thicknesses and area . Veneer thickness Surface area Of specimen Dimension of specimen on a side Procedure to : Ohart find specific : to be used gravity Inches 0.014 to .021 .019 to .029 .028 to .043 : .038 te : .058 1 .056 to : .086 : 1 1 -.076 to 1 . 116 l- 3q.cm. 100 75 100 75 50 37-5 Inches 3-937 3.410 2.784 2.411 Double the scale reading .da. Original Supplementary Original 3.410 1 do : Supplementary 1 3-937 iE ead eoale 1 : directly .do. Original Supplementary — Veneer specimens of theae thlckneaeea will probably be more conveniently cut with a small circular aaw than a paper cutter. Z W 40209 F 0.0 0.0 j u »677j r >f Florida IIIIIIIi.IIIIIIIIH 1 3 1262 08866 6051