How long to leave clamps on during gl…
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Hi everyone.Thanks for all the fabulous threads and answers.I saw my own veneers on my bandsaw and use them to put a pretty face on stock of the same species.It is my way of “optimizing” available stock as it were.Actually it was a technique used quite a bit by the old timers and I use it pretty intensively.
Now this ain’t just a cliche’:a woodworker can never have enough clamps.With this heavy “veneering” technique I use I am always waiting for the glue-ups to cure sufficiently in order to use the clamps.I have tons of clamps but never enough.What is the minimum time in clamps before I can unclamp?I use aliphatic glues mostly,i.e.common white and yellow.Assuming room temp.(70 degrees) and the full cure time is 3-4 hrs. can I unclamp at around 45 min. to 1 hr. or is that to soon?Thanks tons in advance.Roland.
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IMHO, leave the clamps on for the 3-4 hour period, during that time there has got to be something to do, ie-in the shop, feed the dog, have a cup of your favorite beverage, go out for more clamps or glue. Me, I try to do my glue ups at the end of the day or before I have to go off and do something else completely different, that way I know for sure that I'm not rushing anything and an overnight wait can't hurt. Good luck.
*if you want to save yourself some clamps then you can buy or build yourself a vacuum press for veneering. as soon as it the weather gets nicer i plan to build myself one. if you have a way of heating your project after it's been glued up things will set up faster. (be careful though)i used to use a heated press and the glue would cure in about 5 min. i think you would be fine leaving your work in the clamps for about an hour, and letting the glue cure on it's own after that.
*Roland,Hehe, reminds me of little story:Lou Holtz was once asked by a young defensive back on how to cover the pass. Holtz told him, "If they don't throw the ball; come up. If they do throw the ball, drop back and don't cover the decoy; cover the guy they throw to." The young man thought a minute then asked, "But, Coach, how do you know who the decoy is?""Simple", replied Holtz, "he's the one they don't throw to." Gotta keep it simple, man.b ;-)Seriously, though, when I use PVA type glues I generally wait 3-4 hours like Bill.Dano
*Hi Roland,I’m pretty aggressive when it comes to getting something out of clamps. It depends upon how soon I need to cycle the clamps. If you need the clamps than an hour (or even a half hour in the hot weather) is fine. You really just have to wait until the glue grabs not until it cures. But be careful of the piece if you take it out of clamps before the glue cures. You can’t stress it without risking distorting the joints.Of course the opposite applies: if you don’t need the clamps then leave the piece until the glue cures. That way you know you’re safe.Hope this helps.Best,Kim Carleton GravesCarleton Woodworking
*There are two points of time having to do with gluing. The first is the "clamp time" which is the time needed for the adhesive to develope enough strength so that it will keep the joint together without the clamp pressure. However, the joint is relatively weak and no pressure or should be put on it and no machining of the wood should be undertaken. Sanding glue lines at this time will result in latter depressions when the wood fully dries at the glue line. The second is "cure time". Cure time is the time required for the adhesive to fully cure and develope full strength.PVA glues typically will be able to have the clamps removed within 30-60 minutes (the product directions generally give you this info). Cure time is about 24 hours. PVA glues typically work best in temperatures between 65-85 with meduim humidity and reasonalbly dry lumber. The tech rep from the manufacturer of the PVA adhesive I used to use said the the cure time was doubled if the temperature was 55 degrees.
*Roland, The answer is, there are no shortcuts when it comes to gluing veneer. Solid lumber, if it is not stressed can be unclamped in about 15 minutes using yellow glue. Veneer is so thin and soaks up so much water so fast that if the clamps are removed before the glue has set you could have the seams lift, curl or open up do to fast shrinkage. If you use a catylized resin glue like I do, don't even think of removing the clamps before the stated time. If you are going to do veneering on a regular basis get a vaccume bag setup. It's well worth the cost. If you go that route and have problems or questions feel free to e-mail me direct anytime.
*I'm definitely in favor of short clamp time. Yellow glue joints can be unclamped in 10 to 20 minutes, but just as important is to tighten up the clamps some 5 minutes after you originally set them. For some reason (duh) the wood compresses with a clamp on them and if you don't tighten up while the glue is setting you get gaps. On the other hand, if you are glueing a tensioned joint, such as a curve, leave them on over night.
*Roland - sometimes I glue up a scrap piece and clamp it in my bench vise or use spring clamps and will check that before unclamping the main piece. I do this mainly in cold weather when set up time is slower and in doubt. I've had PVA take as short as 1 minute and as long as several hours depending in temp and humidity.
*You're all missing out. Everyone try this once, and if you still say I'm nuts, I'll shut up (but I'll still think you're all wrong):Take four pieces of scrap, prepared to glue together. Whether you do a face lamination or an edge glue up is up to you, it'll work either way - you're going to do two glue ups. Glue two pairs together. In an hour or two, take one out of clamps. Leave the other overnight. In the morning, compare your glue lines. Now tell me that you don't have a better seam with a glue up that's been left in clamps for 24 hours.This doesn't really apply directly to the veneering question, more to the answers, but I think that if you're in a hurry on the veneer, you should hammer it on...SB
*Thanks everyone for the fabulous answers as always. Scott have you tried that experiment by leaving one glue-up clamped a little longer than 1 hr.,perhaps 2 or 3hrs. instead.Perhaps their is an optimum time,not quite the full specified 3-4 hrs. per mfg recommendation,that will give the best,i.e. 24hr.like results,without leaving overnight.That seems like a very good experiment;if the results are obvious as you indicate.When I get the time I think I'll replicate it with various samples.Roland.
*Scott, it depends on the precision of the initial fit. A perfect fit will yield a perfect joint after one hour. A bad fit will spring back and open slightly if the clamps are released to soon. Clamps are supposed to hold the wood in place untill the glue dries not force the wood into place. I get a kick out of the guy that insists on using 3/4 in. pipe clamps because he needs the extra pressure. Do it right and a 1/2 in pony clamp will give you a tight joint.
*Armin, you're both right and wrong. A perfect fit is a perfect fit, and no clamping pressure is going to create a perfect fit out of a bad one. I'm taking a perfect fit as a given - if it isn't, than you're not ready to glue up. my point is that glue does not sit still as it dries and cures, particularly PVA's, which are susceptible to creep even when cured. the clamping is to keep the glue compressed and tight as it cures - if you release the clamp prematurely, the glue line relaxes, and grows thicker. the precision of the initial fit is not a factor here, in fact a more precise joint will illustrate my point better. SB
*Scott, In theory what you claim may be true but I just ran a test sample on cherry. Both sampels cut from the same board, one released after 1 hour the other 24 hrs later. There was no noticable difference after checking with a .001 dial caliper. I sanded them both down, took them to the high school lab and looked under a microscope, looked the same. Maybe I just lucked out.
*Plan a night with your wife.... you know put the project in the clamps, take a shower, take her out to dinner and then, well you know. Leave them overnight.
*"CStanford" Now there is an Idea!
*CStanford-That sounds like good woodworking advice, and EXCELLENT marriage advice!Peace.-Rob
*Thanks, I think it's both.There is no need to hurry a glue up. If you're a pro you ought to own enough clamps or commercial glue racks to get your work done and make a profit; if you don't you're fooling yourself. I promise that I've pulled stuff out of the clamps too quickly and have not always enjoyed the results. Those screw-ups rarely find their way on to these message boards.If you're a hobbyist, why hurry the fun and why take chances with the glue?
*Here's what happens in a glue-up: you clamp it up and check the pressure, it seems okay. The water from the glue causes the wood to expand and due to the clamp it compresses the wood, increasing the pressure. If you check the clamp at the height of this pressure you will think you've got it right. But as the moisture evaporates the wood contracts and the clamps can loosen so much that they can fall off. Unless you tighten them up at that point you are doing no better than taking them off completely.... in other words leaving them on for 24 hours is pointless.
*RJT -never been to your village. apparently it's far from mine. and apparently we're both working, so here we stand, agreed to disagree. what's pointless to you, is hugely important to me. as long as we don't work for each other, we're cool.right?
*The phenomenon Richard describes does happen - usually when too much glue is applied.
*Scott: you are wrong to assume that what is hugely important to you is pointless to me. In fact, you are important to me. Thanks for being here (knots). You are welcome to visit my village, it'd be nice to meet you.
*why, thanks, Richard, that's nice to hear. I don't mean to assume anything, I thought I was quoting you. It's important to me to leave the clamps on overnight, you said it was pointless to you. It's okay, though, I know it's hard to tell in this medium, but I really mean it when I say that we're all welcome to disagree without it meaning that we don't respect one another. don't sweat it, all is cool with you and me...I am, however, beginning to get a little concerned about how often Charles and I have been agreeing lately ;)Scott
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