I am working on hammer veneering the aprons of a series of small, round tables. I have successfully hammer veneered some flat test pieces but these round ones are proving more difficult. The aprons range in diameter (yes, diameter) from 10″ to 20″ and are brick laid poplar cut on the band saw, routed with a template and they got a final smoothing with a rasp. On the outside I am trying to apply a shop sawn walnut veneer that is about 0.050″ thick. Each apron will have three or four pieces of veneer with the seams covered by legs or other features so they don’t have to be perfect. I soaked the veneer pieces in hot water, bent them around a form and let them dry so that they have pretty close to the right curve before trying to put them down. I am using 150g bloom strength hide glue from Lee Valley.
I put hide glue on the substrate and both sides of the veneer and then started hammering. I could not get the glue to grab even after about 10 minutes of hammering. I eventually clamped the ends down and let it dry overnight. After drying overnight the glue held fast but there is a large air pocket in the test piece surely because it was not hammered home but held by clamps on the ends.
I have thought of a few things to do differently in the next try:
1) size the substrate with diluted glue and let it dry beforehand
2) switch to higher gram strength glue – I have some 260g I could try
3) don’t heat the substrate (room was about 65deg, substrate maybe 75deg)
4) add a little vinegar to the glue – this is supposed to increase the initial tack(?)
5) have some shaped calus ready and clamp up the whole thing
I would like to avoid the last one if possible. Any other suggestions would be most welcome.
Chris
Replies
I'm no expert by any means, but my understanding is that you have to let the glue dry a bit before you start hammering. Really just an educated guess...
Chris
I could be wrong, but even if your glue holds, my bet is that the wet wood would be trying to tear itself off when it dried. Even if it stays down, it should be full of checks
I like to use epoxy for veneering, because it contains no water, so if the veneer and substrate are at EMC, then there are no built-in stresses between them.
You could mix some up, thicken it, and use it as thick as you want. Clamp a thin caul from something like hardboard mdf, or plastic laminate, with a sheet of 1/8" packing foam in between, and just clamped with spring clamps. Set it close to the heater over night, and it will be done in the morning.
Keith,
To be clear, the wood is not wet when I am trying to hammer veneer it. I soak the veneer in hot water, bend it around a form and then let it dry for several days. The dry veneer then has a curve to it that is very close to the shape of the apron. Maybe 1/8" to 1/4" of spring back. There was no checking in the test piece I got down, just an air bubble.Epoxy would probably work here but I would have to make a set of cauls of the exact diameter of each of the aprons (4 different diameters from 10" to 20"). Thin cauls of MDF would never bend that tight. I was trying to avoid making lots of cauls and everything I have read about hammer veneering seems to imply that it should work for this application. I suspect my lack of skill/practice is the problem.hdgis1 may be correct that I have to let the glue dry a bit before I start hammering.
Chris
This doesn't sound like any hammer veneering problem I've had. Sound like you did everything right. Can you try some other hide glue. Perhaps that may be the problem.
Thanks RonK, I will try some other hide glue. This batch did work fine for a flat piece I tried - a scrap of the same walnut veneer on some plywood, but I am looking for any ideas that may help.Mufti - Thanks. I will keep the clamp/caul/sandbag idea in mind if I can't get it to stick after hammering out the air and excess glue.
Chris
Edited 2/2/2009 5:19 pm ET by cwalvoord
The tighter the bend, the thinner the caul needs to be. Most of the time, I would vacuum-bag this kind of project with the form outside of the bag, and at a 10" R, I would use plastic laminate as the caul, and would probably just do a laminated bend with a very simple flimsy form of 1/4" mdf. But since you mentioned how you had started with sawn substrate parts, I was adjusting my suggestion to fit what you had started with. Sticking with that train of thought, you could wet out the veneer and substrate with un-thickened epoxy, then mix what is left as thick as peanut butter, then spread it out over a chain sawn surface for that matter, then clamp the veneer with a couple of layers of plastic laminate with the foam between to spread out the pressure, and get away with murder, so to speak for craftsmanship, and still have it work.I know about good craftsmanship, but I know how to compensate for lack of it as well. Everyone makes mistakes sometimes. The sign of a good craftsman is knowing how to correct your mistakes and learn from them. "Learn" is the key word, and the best part.
The point of hammer veneering is to squeeze out bubbles of air or excess adhesive between the contact surfaces, something a vacuum press does using atmospheric pressure. The hammer does nothing else, it will not ensure the success of the operation.
Roughly shaped cauls and intervening sand bags (warmed in the oven) should hold the parts together until the glue works, nails on the outer surface of the caul allowing strings to pull all up tight. Hope this helps.
Chris,
I think the changes you are going to make will get you the results you are after.
A couple of other things that may help are:
Mix the glue a little bit thicker than you normally would for hammer veneering.
Get the veneer hammered down, without worrying too much about a few bubbles. In about a half hour go back and with an iron re-heat the glue and hammer the problem areas down again. They should go down much easier. In fact you can still hammer down the bubbles on table you have already made, you just have to use a hotter iron and spray the bubble with some distilled water.
Rob Millard
http://www.americanfederalperiod.com
Thanks Rob, I was hoping you would chime in here. I have read pretty much everything you have posted on your web site and blog and learned a lot from it. Your work is inspirational.I will give this another shot with the changes everyone has suggested and see how it goes. I will try to iron down the air bubble in the test sample too. The void is right on the edge so I may try spritzing a little water or glue directly into the pocket and then ironing it down.Thanks again to everyone for your suggestions.
Chris
I would add that when you do iron down the veneer do not make the iron too hot. It will liquify the hide glue and you will then have to go over it with the veneer hammer again, and it may still pop up. If the iron is just hot enough to make the glue tacky again but not totally liquify it, it will be easier to re-hammer. I agree with Rob about making it a little extra thick.
You can also inject a little more glue into the bubble with a syringe through an xacto knife punture, then hammer it, then if needed weight it down with a sand bag.
A vacuum press also works well but you'll have to make an MDF form to support the curvature of your apron.
Good luck,
Jay
Another method that I really like, and one that was illuystrated on the cover of FWW a few years ago is when you apply yellow glue to both surfaces, let it completely dry and then iron down the veneer. The iron re-actives the clue and requires no clamping. The bond is instant and is unbelieveably strong. The flat iron works great on convex surfaces. Concave surfaces are more tricky, but for that I have heated a copper pipe with a propane torch to serve as an iron and rolled it over the surface, and that does work. The temperature is harder to regulate and you can burn the wood if you'r not careful or if you don't keep the pipe rolling. This would apply for whatever backing veneer you are using on the back of your apron. Remember youhave to put the same number of layers ont he back of the substrate as the front.
Jay S.
Jay,Have you used this method? Does running the iron over the glue make a really big mess? And I don't suppose that the iron could still be used on clothes afterwards. Maybe just shop clothes.Chris @ http://www.flairwoodwork.spaces.live.com(soon to be http://www.flairwoodworks.com)
- Success is not the key to happines. Happiness is the key to success. If you love what you are doing, you will be successful. - Albert Schweitzer
I have used this method and the iron gets trashed if you use it to re activate hide glue. (this is because both surfaces have the glue on them.) If you only use it to re-activate yellow glue it is possible the iron could stay clean but don't count on it. You will have the opportunity to gain brownie points with your wife by taking her old iron for the shop and getting her a new one.
Jay
Not to sound like a smart .... but temperature can have a negative effect if your project is cold. As long as you have some glue between the veneer and the sub, you should be able to reheat with an iron and keep on trying. If its any comfort, it has happened to me when I started out and it comes up from time to time. Good news: stay with the hide you can repair and retry again and again.
hang in there
I will keep trying, thanks. I heated it up with the iron last night and got one side down only to have an air bubble form on the other side. As someone suggested, I probably had the iron too hot. I will inject a little glue and keep practicing. I am getting close enough that I think it will be a pretty efficient process (at least for me) once I get it all figured out. Thanks for the encouragement.
Chris
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