+* United States @ Department of 

Agriculture Comparison of Glue-Line 

Forest Service Quality Between Gang Edging and Straig ht-Line Ripping Experiment Station 

Research Paper 

NE-588 

1986 Charles J. Gatchell James R. Olson 
The Authors 

Charles J. Gatchell received his bachelor's degree in forestry from the University of 

Massachusetts in 1955. After a tour of duty with the US. Navy, he returned to the 

New York State College of forestry at Syracuse University where, in 1961, he 

received his master's degree in wood-products engineering. From 1961 to 1965 he 

was a project scientist in the product and process development project at the Forest Products Laboratory in Madison, Wisconsin. Since 1965 he has been project 

leader of the Low-Grade Hardwoods Utilization Research Work Unit at the Forestry 

Sciences Laboratory of the Northeastern Forest Experiment Station at Princeton, 

West Virginia. 

James R. Olson received his bachelor's degree in forestry from the University of 

California at Berkeley in 1971. He did research in wood quality, drying, and preservation at the University of California Forest Products Laboratory until 1979. During 

this period he obtained his master's degree in 1974 and his Ph.D. degree in 1979 

in wood science and technology from the University of California at Berkeley. For 

the past 5 years he has been an assistant professor in the Department of Forestry 

at the University of Kentucky doing research in utilization of low-grade, underutilized or fast-growing hardwoods. 

Manuscript received for publication 21 January 1986. 

Abstract 

Gang edging with a dip-chain fed gang ripsaw produces gluing surfaces equal to 

those from a straight-line ripsaw in yellow-poplar (Liriodendron tulipifera) and red 

oak (Quercus rubra). Special care in gluing red oak was needed to get shear 

strengths equal to solid wood values. However, the strength comparisons between 

sawing methods showed no differences between gang edging and straight-line 

ripping regardless of gluing procedures. 
Introduction 

Gang ripping can be used with No. 2 Common lumber to 

produce more long lengths than the furniture and cabinet industries need (Gatchell et al. 1983, Gatchell 1986, Araman 

et al. 1982). Gang edging (gang ripsaw arbor set with several pairs of blades at varied spacing) is a key step in the 

utilization of small-diameter logs for furniture and cabinets 

through the new System 6 process (Reynolds and Gatchell 

1982). Gang edging or gang ripping to glue-line quality 

edges is required in System 6 and is desirable in the design 

of new manufacturing sequences for the conversion of lower 

grades of lumber. 

Some potential users of the new System 6 technology have 

questioned whether the surfaces from gang edging were 

of comparable quality to the state-of-the-art edges made on 

the straight-line ripsaw. The general feeling was that gang 

edging to glue-line quality surfaces might not be possible for 

the more dense hardwoods. The basic question was 

whether the wood could be held securely enough during 

sawing to produce the quality needed. This study was conducted to determine whether a dip-chain fed gang saw could 

produce glue lines of strengths comparable to those from a 

straight-line ripsaw. 

Materials and Methods 

A dip-chain fed gang edger and a straight-line ripsaw were 

used. The gang edger was a conventional dip-chain fed 

gang ripsaw set up with five pairs of saws to cut widths from 

1% to 3% inches in %-inch increments (Fig. 1). In each 

pair the right-hand saw was used to make a hogging cut. 

Each hogging saw blade was made from 0.254-inch-thick 

steel plate and had a ?&inch saw kerf. The left-hand gang 

edger blades and the straight-line ripsaw blades were made 

from 0.134-inch-thick plate with a %-inch saw kerf. 

Saws in each machine ran at about 3,500 rimin (revolutions 

per minute). The gang edger had 12-inch diameter saw 

blades with 30 carbide-tipped teeth per blade and a feed 

speed of 58 filmin (feet per minute). The saw tooth hook angle was 20 degrees. The straight-line ripsaw blade was 14 

Figure 1 .-The arbor of the dip-chain fed gang edger contains five pairs of blades. 
inches in diameter with 36 carbide-tipped teeth, and the feed 

speed was 65 ftimin. The hook angle was 10 degrees. The 

combination of feed speed, saw diameter, number of saw 

teeth, and saw rimin resulted in a bite per tooth for all 

blades of 0.007 inch. 

The analysis of glue-line strength was based on two separate studies. The first approximated our routine panel lay-up 

procedures. We made panels of three lengths containing 

pieces of three different widths sawed from lumber taken at 

random from an existing supply. A diffuse porous hardwood, 

yellow-poplar-tiriodendron tulipifera, and a ring porous 

hardwood, northern red oak-Quercus rubra, were used. ' When the results showed about a 20 percent reduction in 

shear strength between solid wood and glued-up panels in 

oak, a second study was run. The second study was very 

closely controlled and attempts were made to ensure that 

each panel was constructed as identically as possible with 

all others. All panels in both studies were glued using the 

same room-temperature setting polyvinyl acetate adhesive. 

Study One-Routine Panel Lay-up 

Procedures 

To compare glue lines from the gang edger and straight-line 

ripsaws with routine panel lay-up procedures, edges were 

prepared with each machine and included in each panel as 

shown in Figure 2. We ran enough pieces of % yellowFirst piece in 

the glue Clamps Straight-line ripped glue lines 

t t 

Gang edged glue lines 

21. 33 

or 60 

inches 

Figure 2.-Study One blank layout sequence 1'. Sequence 2 

had the 1 M-inch strips on the right side (layed ;up last) of 

the panel. Sequence 3 had the 3%-inch-wide strips layed up 

first and the 2%-inch strips layed up last. 

poplar and red oak rough dimension, at about 7 percent 

moisture content, through the gang edger to lay up 24-inchwide panels in combinations of 1 %-, 2%-, and 3%-inchwide pieces. To produce the straight-line ripped edge, gang 

edged pieces were randomly selected and a rip cut was 

made about 1/4 inch in from one edge. Panel lengths were 

21, 33, and 60 inches. We made enough panels so that 

each piece width group was glued up first, second, or last in 

the lay-up sequence. Each of these arrangements was replicated twice. Thirty-six panels were made (2 species x 3 

lengths x 3 lay-up sequences x 2 replications). 

In laying up the panels, glue was applied with a flexible stick 

that produced a thick, bubble-free glue spread. Glue was 

applied to only one side of the glue line. Pieces were layed 

up with the first and last pieces directly in contact with the 

glue clamps. A pressure of 200 lb/in2 (pounds per square 

inch) at the glue line was applied, and panels were left in 

the clamps for at least 1 % hours. The finished panels were 

cured for at least 2 weeks before samples were taken for 

testing. 

The block shear test (ASTM 1984) was modified since testing was restricted by the thickness of the panels. The panels 

were first sanded to 0.75 inch. The block shear sample 

dimensions we used are shown in Figure 3. The shearing 

cross section,was 0.75 x 1.5 inches or 1 .I 25 square 

inches. Three, five, and seven shear block samples were 

taken from each of the 21-, 33-, and 60-inch test glue lines, 

Figure 3.-Dimension of the block shear samples. 
respectively. Samples were removed at positions equidistant 

from the panels' ends and from each other along the glue 

line. An equivalent number of solid wood samples were 

taken along two of the panel's 3%-inch strips. 

The block shear samples were placed into a constant temperature (70°F)-humidity (66 percent) cabinet until a constant 

weight was obtained. A standard shearing tool was used to 

test the maximum load at failure for each sample at a head 

speed of 0.02 inch per minute. Maximum shear strength 

in pounds per square inch was determined for each block 

shear sample. Moisture content was determined immediately 

after shear testing. 

Study One-Results and Discussion 

A preliminary examination of the data for individual samples 

showed that there was no loss in shear strength across 

the width of the panels due to lay-up procedures. Thus, 

even though it takes almost 3 times as long with our techniques to spread the glue on a 60-inch-long piece as on 

a 21 -inch-long piece, our procedures were adequate for 

good glue bond formation. 

Average shear strength values for red oak and yellow-poplar 

are given in Table 1. Moisture content at the time of test 

was about 11 percent. A statistical analysis showed no significant difference between glue joints prepared with either 

the straight-line ripsaw or the gang edger. There was also 

no significant difference between the pairs of blades in the 

1 %-, 2%-, or 3%-inch bays of the gang edger. 

As expected, the red oak shear strength values were higher 

than those for yellow-poplar. The values for the glued-up 

and solid wood yellow-poplar samples were about the same 

reflecting the more uniform nature (diffuse porous with thin 

rays) of this less dense wood. We did not, however, expect 

to find a 20 percent strength reduction when comparing 

red oak glued samples to solid wood samples. There may 

have been an interaction of small shear block size and the 

weakening effects of pronounced earlywood vessels or large 

rays that are typical of red oak. There was no increasing or 

decreasing trend in the strengths of individual samples as 

we proceeded from the first glue line to the last glue line in a 

panel. Thus, if there was some machining, gluing, or testing 

procedural error, it was consistent enough not to show up 

in the comparisons of the two sawing methods. 

As the glue-line preparation procedures were considered 

equivalent for the two sawing methods (gang edging and 

straight-line ripping), all values for each method were averaged to obtain indicator values with standard deviations 

for length (Table 2). We include standard deviations in Table 

2 to give the reader an appreciation for the variability of the 

Table 1 .-Average shear strength values for red oak and yellow-poplar wood and glue lines - - 

Panel Strip Gang Straight-line Solid 

Species length width edgera ripsawa woodb 

Inches Inches ---------------- Average shear strength (Iblin? ---------------- 

Red oak 2 1 1.5 1,788 1,901 2,301 

2.5 1,693 1,798 2,301 

3.5 1,812 1,891 2,301 

60 1.5 1,260 1,201 1,284 

2.5 1,286 1,332 1,284 

3.5 1,289 1,295 1,284 

aGlue-line averages for the 21-, 33-, and 60-inch panel lengths were determined from 18, 30, or 42 block shear samples, respectively. 

b~olid wood averages for the 21-, 33-, and 60-inch panel lengths were determined from 36, 60, or 84 block shear samples, respectively. 
Table 2.-Study one--shear strength average values for red oak and yellow-poplar glued-up and wood samples 

(standard deviation in parentheses) 

Panel Gang Straight-line Solid 

Species length edgera ripsawa woodb 

Inches ......................... Average shear strength (Iblin2) .......................... 

Red oak 21 1,765(226) 1,863(171) 2,301 (260) 

33 1,636(174) 1,669(171) 2,080(192) 

60 1,647(208) 1,626(238) 2,087(278) 

"Glue-line averages for the 21-, 33-, and 60-inch panel lengths were determined from 54, 90, or 126 block shear samples, respectively. 

bSolid wood averages for the 21-, 33-, and 60-inch panel lengths were determined from 36, 60, or 84 block shear samples, respectively. 

data. Ninety-five percent of all individual sample values 

will be within plus or minus 2 times the standard deviation. 

Larger deviations, therefore, show a wider range of values. 

The results clearly show that the dip-chain fed gang edger 

produces glue lines in oak and yellow-poplar that are equivalent to those obtained from a straight-line ripsaw. In oak, 

the 33- and 60-inch average shear strength values were 

very similar. The averages for the 21 -inch panels were 

higher, but this was attributed to the higher average shear 

strength for the wood from which they were made. The averages for the yellow-poplar glued-up samples were very similar, ranging from 1,269 to 1,315 lb/in2. 

Study Two-Close Production Control 

Because the red oak glued samples in Study One were 20 

percent lower in average shear strength than the solid wood 

samples, a partial retest was done under close production 

control. Boards from an available kiln-dried red oak lumber 

supply were selected for straightness of grain and 4-inchwide strips were sawed out. These were crosscut to pieces 

33 inches long and passed through the 3-inch-wide pair of 

saws. Each panel contained three pieces, two of which were 

re-edged on the straight-line ripsaw and glued together. 

The other glue line was made from gang-edged surfaces. 

Panel construction is given in Table 3. Ten panels were 

glued up as shown in Figure 4 using the following procedures for each: 

Table 3.-Study two-shear strength of glued up and solid red oak samples, in pounds per square inch 

Panel construction Glue joint preparation Solid wood I 

Panel 3 pieces 3 pieces Gang edger Straight-line ripsaw 

No. same same Random Standard Standard Standard 

strip board pieces Averageb deviation Averageb deviation Averagec deviation 

5 * 2,233 376 2,374 242 2,253 400 

2 2,412 142 2,265 124 2,253 378 

3" * 2,161 334 2,192 270 2,402 274 

4" * 2,418 224 2,154 98 2,402 274 

1 * 2,302 263 2,254 280 2,287 373 

6 2,329 21 1 1,817 271 2,283 444 

i 7 2,205 245 2,369 253 2,367 302 

8 * 2,100 198 2,019 498 2,248 471 

9 * 1,993 31 2 1,890 199 2,056 599 

10 * 2,012 113 1,864 483 2,223 481 

"Panels 3 and 4 were made from six pieces from one board. Therefore, a single mean and standard deviat~on based on 34 samples were 

I co~puted for the solid wood from both. 

Average of seven values. 

"Average of 17 values. 
Straight-line 

ripped glue lineFigure 4.-Study Two blank layout. 

1. Edges were prepared by sawing. 

2. Within 10 minutes of sawing, glue was applied with 

flexible sticks to achieve a thick, continuous, bubble-free 

spread on one side of the glue line. 

3. Square steel tubing was used between the glue clamps 

and the outside panel edges to ensure even pressure distribution. 

4. A 1 -minute closed assembly time was employed before 

application of 200 lb/in2 clamp pressure. 

5. Clamp time equaled 1 hour 30 minutes. 

The next panel was begun only after the preceding panel 

was in the glue clamps. The panels were cured for at least 1 

week before surfacing and for at least 2 weeks after surfacing before shear samples were prepared. he average moisture content at the time of testing was 8.5 percent. 

Study Two-Results and Discussion 

The shear strength value averages and standard deviations 

for the close production control red oak samples are given in 

Table 3. A statistical analysis showed no significant differences among the panels or between the dip-chain fed gang 

edger and the straight-line ripsaw at the 5 percent significance level. I 

I 

and earlywood vessels formed a plane of weakness at right 

angles to the rays. The thin (0.75 inch) samples gave these 

planes unusual importance when the plane of shear was 

lined up with either rays or earlywood. Figure 5 shows two 

solid wood samples taken a few inches apart along the grain 

from the same piece of wood. Sample 5-1 0C was the weakest sample of the entire study with a shear strength of 745 

lb/in2. About three-fourths of the failure surface was in or on 

both sides of a single ray. Sample 5-9C was taken from 

the same strip of wood just a few inches away. The orientation of the rays appeared to angle out of the shear plane 

enough so that other wood elements were brought into play. 

The result was a shear strength of 2,587 lb/in2, one of the 

higher values of the study. 

Figure 6 shows characteristic failure of solid wood (no glue 

line) samples when the rays and shear plane are not 

aligned. The failure shown has run out to the unsupported 

end of the sample. The saw tooth appearance of the broken 

surface is the result of failure going across a growth ring at 

or very near a ray, then turning at right angles along the 

earlywood of the next growth ring before again turning at 

right angles along another ray. In studies such as this, a 

predetermined orientation of the growth rings to the shear 

plane is not possible. It is a source of variation that is worth 

mentioning, however. 

The solid wood and glued-up average shear strength values 

were about the same in Study Two. These averages were: 

Shear strength (Ib/in2) 

Standard 

Average deviation 

Gang edger 2,217 280 

Straight-line rip 2,120 343 

Solid wood 2,268 441 

As a comparison of the standard deviations shows, the 

glued-up samples varied less than did the solid wood samples. This was not entirely unexpected. As mentioned earlier, a ray or a zone of earlywood vessels contained in most 

or all of the plane of failure will cause low strength values. 

The chance of this occurring when two different pieces of 

wood are bonded together is considered to be far less likely 

than when solid wood pieces alone are considered. In a 

practical sense, we cannot really do better than equal the 

properties of the wood itself. 

In general, the greatest variability occurred in the solid wood 

samples. Rays formed a plane of weakness in one direction 
Figure 5.-One of the strongest (5-9C) and the weakest (5-1 0C) solid wood samples came from the same piece of 

wood and were only a few inches apart along the grain. 
Figure 6.-Shear failure tends to run along rays and in the earlywood vessel zone giving a saw-toothed 

appearance to the failure on the unsupported end (label covers supported end of shear sample). 

Summary 

To be able to gang rip lumber to glue-line-quality edges is 

an important hardwood processing capability. The dip-chain 

fed gang edger or gang ripsaw is superior to roller fed gang 

saws in holding wood stock steady during sawing. However, 

potential users have questioned whether the dip-chain fed 

saw can produce glue-line surfaces equal in quality to those 

from a state-of-the-art straight-line ripsaw when machining 

hardwoods. The results of this study clearly show that these 

saws produce glue joints of equal strength in yellow-poplar 

and red oak in lengths from 21 to 60 inches. 

Literature Cited 

American Society for Testing and Materials. Standard test 

method for strength properties of adhesive bonds in 

shear by compression loading. In: 1984 Annual Book 

of ASTM Standards. Vol. 15.06. Philadelphia, PA: American Society for Testing and Materials; 1984; 36-39. 

Araman, Philip A.; Gatchell, Charles J.; Reynolds, Hugh W. 

Meeting the solid wood needs of the furniture and 

cabinet industries: standard-size hardwood blanks. 

Res. Pap. NE-494. Broomall, PA: U.S. Department of 

Agriculture, Forest Service, Northeastern Forest Experiment Station; 1982. 27 p. 

Gatchell, Charles J, Impact of rough mill practices on 

yield. In: 1985 Eastern Hardwoods Conference; I985 

September 9-1 1 ; Harrisburg, PA. Madison, WI: Forest 

Products Research Society; in press. 

Gatchell, Charles J.; Anderson, R. Bruce; Araman, Philip A. 

Effect of gang-ripping width on C1 F yields from 

No. 2 Common oak lumber. Forest Products Journal. 

33(6):43-48; 1983. 

Reynolds, Hugh W.; Gatchell, Charles J. New technology 

for low-grade hardwood utilization: System 6. Res. 

Pap. NE-504. Broomall, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment 

Station; 1982. 8 p. 

*U.(I. GOVERNMENT PRlNTlNO OFFICE1 9 8 6 -6 0 5 LO 2 6 14 0 0 1 3 
Gatchell, Charles J.; Olson, James R. Comparison of glue-line quality 

between gang edging and straight-line ripping. Res. Pap. NE-588 

Broomall, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station; 1986. 7 p. 

Gang edging with a dip-chain fed gang ripsaw produces gluing surfaces 

equal to those from a straight-line ripsaw in yellow-poplar (Liriodendron tulipifera) and red oak (Quercus rubra). Special care in gluing red oak was 

needed to get shear strengths equal to solid wood values. However, the 

strength comparisons between sawing methods showed no differences between gang edging and straight-line ripping regardless of gluing procedures. 

I ODC 836.1 

I Keywords: Furniture, panels, rough mills, lumber processing 
Headquarters of the Northeastern Forest Experiment Station are in 

Broomall, Pa. Field laboratories are maintained at: 

Amherst, Massachusetts, in cooperation with the University of 

Massachusetts. 

Berea, Kentucky, in cooperation with Berea College. 

Burlington, Vermont, in cooperation with the University of 

Vermont. 

Delaware, Ohio. 

Durham, New Hampshire, in cooperation with the University of 

New Hampshire. 

Hamden, Co~ecticut, in cooperation with Yale University. 

Morgantown, West Virginia, in cooperation with West Virginia 

University, Morgantown. 

Orono, Maine, in cooperation with the University of Maine, 

Orono. 

Parsons, West Virginia. 

Princeton, West Virginia. 

Syracuse, New York, in cooperation with the State University of 

New York College of Environmental Sciences and Forestry at 

Syracuse University, Syracuse. 

University Park, Pennsylvania, in cooperation with the 

Pennsylvania State University. 

Warren, Pennsylvania.