Veneering redux

H

HSteier

Well-known member
Well I'm moving along with my veneering, panels all cut etc. I glued up the first panel with unibond 800 with good result EXCEPT a few small glue starved spots on one edge. What is the best way to deal with this. I can inject white or yellow glue and clamp but I'd be concerned that this wouldn't hold because the unibond probably sealed the wood. Epoxy would hold but I'm not familiar with any epoxy thin enough to inject with a syringe. What about methylmethacrylate? I think I can draw the very thin type into a syringe.

All help appreciated

Howard Steier
 
Based on the chemistry of Unibond (urea formaldehyde), I think you're going to be forced into the use of an epoxy-type or cyanoacrylate glue.  According to Marc Adams in the latest issue of Popular Woodworking, both hide glue and PVA types (yellow and white) depend on water adsorption into the wood to be effective, and as you noted, the Unibond has probably sealed both the substrate and the veneer. 

One thing that may be an advantage is the surface characteristics of urea formaldehyde - the cured surface should be quite polar, so cyanoacrylate should bond pretty well to it.
 
Howard,

I would be cautious about using an epoxy in patches. I have used epoxy resin to bond veneers, and it is sufficiently intrusive into the grain of the veneer from the back that , while there was no evidence of the epoxy on the surface, it clearly acted as a filler/sealer and changed the stain absorbtion characteristics of the veneer.

Karl
 
I asked the manufacturer (vendor of Unibond 800) what they thought. They said that yellow glue would work. Darryl Keil responded, he's the author of a video on vacuum veneering, so I assume he knows what he's talking about. So I tried the yellow glue and it is holding nicely. It remains to be seen what will happen in 20 years but by then I'm not going to be around to worry about it.
I did repair one void with methylmethacrylate but the excess on the veneer was a royal pain to clean up.
I'll clamp more carefully next time.

Another thing. My substrate is a panel of 2" poplar strips glued up; it's perfectly flat. I veneered both sides at the same time. When it came out of the press it was bent, concave on the face side that had the mahagony crotch. I had to wet down that face to remove the glue tape and when I was done, the panel was flat. So far it's staying flat. I assume the initial bend was from differential water absorption that subsequently evened out. But now I'm a little afraid of veneering the other wooden panels. I'm tempted to make (uggh) MDF panels. Any comments?

Howard Steier
 
Well, assuming you're putting the veneered panels into a frame (for a paneled door, for example), it really shouldn't matter if they come out of the press with slight warping.  As you noted, you can pretty easily straighten out warps that aren't too bad by laying a damp towel on the concave side, and warming the convex side with a heat gun.  Once that's done, you can either stack and sticker it on a flat surface with a lot of weight on it and wait a couple of days, or machine it quickly and capture it in a door frame.
 
Howard, I can only eco this sound advice? (One thing I was instructed about as a apprentice? making the glue an even covering, and being hasty)

                                                          Joseph Hemingway
 
Gentleman please forgive me for being off topic . I have a veneer press that must be 70 years
old. It has 23 screws and can press a 4'x 10' with about 150 lbs per sq in. I used it to make
conference  tables . I had a stroke and no longer make anything but would like to sell the
press. Can you tell me where to list it .
Thank You
                                [email protected]
 
Near the bottom of the page is a for sale section. This would be the best place to list it.
 
Howard, forgive me if I'm reading this wrong but it sounds like you put the panel in the bag all by itself? If that's the case that explains why you ended up with a potato chip! You have to have something in the bag to suck the panel flat to. The best thing for this is a piece of a granite countertop that someone ordered wrong or miscut. A local shop might even give the piece away if it's to small for them to use on a vanity. If this seems a bit excessive glue 3 or 4 pieces of mdf together and let them cure well. I hate that stuff too but it won't actually be part of the panel, just next to it! Either way be sure to round over all the edges so you don't poke a hole in the bag! One last thing, your 2" poplar strips.... that was 8/4 you ripped down to 3/4 to get vertical grain right? If not you may have trouble down the road. Flat sawn poplar can be surprisingly "mobile"!
 
Hi Mark
Actually, I didn't use a bag; I have a home made press so there was strong support on both sides of the panel during the glue-up. Over the past couple of weeks the panels have flattened out almost completely. I think the original curvature was indeed from differential water absorption during glue up.

Howard Steier
 
Howard, having read your last info? I repeat (One thing I was instructed about as a apprentice? making the glue needs an even covering, and not to be hasty) This makes the glue pentrate right through the venner in a hand press, so no air pockets exist.

                                           Joseph
 
Thank's Fran, I think I was being hasty with  my explaining, but a Rush - and lastly in a hurry.

                                                    Joseph
 
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