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Hardwood Record — Veneer & Panel Section 



March 10, 1917 



Pointers for Veneer Users 



Have You Ever Considered the Part Glue Stresses Play in Warping? 



Read This Suggestion 



HERE are several pointers for the average veneer 

 user to observe in doing fine face veneer, and 

 especially in matching up work. TTie first is 

 that of moistening fine face veneer before using 

 it. Some moisten it with a steam jet, others sponge it 

 with hot water, while still others spray it. What will 

 be best in your own case can be determined by a 

 little practice. Generally, it is better to get some heat 

 in the moisture, because it penetrates and is more 

 effective in softening the wood. It is not best to have 

 the veneer too wet. What is wanted is just enough 

 moisture to soften it, after which it can be put be- 

 tween two hot cauls or apparatus, and pressed per- 

 fectly flat, taking out all wrinkles. It can be trimmed 

 and handled without much danger of breaking and 

 splitting. It may seem that this would have a tendency 

 to cause a little swelling, and thus the veneer face would 

 be inclined to crack after it is finished. However, it is 

 contended by old veneer men that if the moisture is used 

 judiciously and the veneer handled right, it is much the 

 better way to use it, and it is practically the only suc- 

 cessful way to handle thin fine face veneer. The other 

 point that needs attention is that of keeping it in the 

 clamps longer. 



There seems to be a common impression that as soon 

 as the glue sets until it holds the work, it can be released, 

 but the fact of the matter is that glued work is taken out 

 of the clamps too soon. If it were possible to do so, it 

 would probably be better if glued work could be kept 

 in the clamps until every vestige of moisture had dis- 

 appeared and all the strains had worn themselves out, 

 just as we would keep a piece of bent work in the press 

 drying, or rather clamped up in forms, for some time. 

 Men who have studied this question contend that no 

 good job of glue work should be released from pressure 

 short of twenty-four hours, probably forty-eight, and 

 even seventy-two would be better. 



It is likely, by keeping stock in the clamps longer, we. 

 could get rid of a whole lot of slight warping and twist- 

 ing, because the strains would have disappeared. If the 

 veneer is kept flat in the presses it would remain that 

 way unless strains are set up anew by coming in contact 

 with moisture. Not only that, but the glue gets more 

 firmly set and has better grip on the wood. Just how 

 long glue continues to harden in setting seems to be an 

 uncertain matter, but it is evident it is not through set- 

 ting in twelve hours. It may get hard and sticky, and 

 dry out enough, so far as we can see, that it holds firmly 

 but really it is not through setting until all the moisture 

 has disappeared, and until this happens even the glue 

 itself, in the process of setting, is likely to set up strains 



in the work. Consequently, where we have particular 

 work, it must be given plenty of time in the press. 



This thing of glue setting up strains in the process of 

 setting brings up another point — the effect that glue itself 

 may have on a piece of work. We very seldom give 

 consideration to this: we consider glue as a cemeting 

 material purely, and seldom calculate that while it does 

 cementing, it may also be responsible for some of the 

 strains. If you want to demonstrate this, try gluing a 

 piece of veneer onto a solid plank. That is, glue veneer 

 on one face of it. Take a plank, no matter how dry, or 

 whether it is 1 -in. thick or 2-in., smooth off one face and 

 glue just a thin sheet of face veneer on it, and the chances 

 are about nine to one that it will distort the plank; it will 

 bend it toward the glued face, and probably also cup it. 



There has been much argument about glue joints on 

 the edge of lumber shrinking, and doing this and that, 

 but did you ever consider that glue itself probably sets 

 up some strains in the wood? Take liquid glue and 

 spread it on the face of a board for venering, then apply 

 a sheet of veneer and put it under pressure. Now, this 

 glue is a mixture of water to quite a heavy percentage, 

 and in the process of setting the water is taken up first, 

 you observe, by the wood, then eventually part of it 

 evaporates into the air. Anyway, it disappears and the 

 glue dries out. Now, if that glue is left in a solid mass to 

 dry out, it is pretty likely that as the moisture disappears 

 the glue will shrink in volume considerably. Being 

 spread in a thin layer on the lumber, it may shrink 

 slightly in thickness in drying out, but if clamped down 

 it has no chance for what we might term general shrink- 

 age in bulk, but it has a cohesiveness, one particle for the 

 other, as well as an adhesiveness for the wood itself and 

 unquestionably it must have a mighty strong tendency to 

 shrink together and draw itself into a smaller bulk, and 

 it is this which sets up the strains in the wood and makes 

 a board cup and bend when faced with a piece of thin 

 veneer on one side and nothing on the other. 



Now, then, suppose we face the board on both sides 

 with a piece of veneer. We maintain a balance then and 

 prevent its warping seriously, but we do not dispense 

 with the strains that are set up in the process of gluing. 

 We simply have one on either side, to counterbalance, 

 and they are hard at work just the same, and just as hard 

 as ever. Probably they eventually disappear when the 

 glue is thoroughly set and dried out, but the fact that 

 they are set up is one of the strong arguments in favor 

 of keeping stock clamped up in presses until every bit 

 of the moisture is evaporated, the glue is thoroughly set, 

 these strains have exhausted themselves, and the work 

 comes to a rest. M. A. N. 



