Hello All,
I seem to be missing something while trying to veneer panels in my veneer press bag. I’m actually veneering over some 3/4″ maple and oak faced ply-wood I’ve had sitting around for a couple of months with some fabulous ripple mahogany. It’s going to be a hanging DVD “cabinet” minus any doors…so I’m not using a lesser “backer” grade veneer for the insides as you will see the insides all the time. Since it’s for DVDs my pieces are not that larger either.
I’m using a dark veneer press glue, a 4×4′ lower “batten” of MDF and a breather mesh on top of my pieces. I’ve been veneering (vacumming) one side of my panel for 45 minutes, then removing it, fliiping it over, and veneering (vacumming) the other side. Trouble is when I take it out of the press the panel (regardless of size) always has a “cup” to it.
Should I be using a top batten instead of a mesh fabric? I like the fabric because I can see whats going on during the pressing and can abort real quick if I need to adjust something thats slipped or missed something. Or am I doing something out of sequence with my procedure? Perhaps I need to veneer both sides at the same time? Is 45 minutes enought time for the plywood to develop a cup that won’t equalize when the other side is done? Would this be the case for all substrates that might be used like solid wood or MDF?
If I should be vennering both sides at the same time heres an additional question. Since I’m using a large 4×4′ 3/4″ MDF base as a bottom batten in my veneer bag, how do I ensure that any squeeze out will not adhere my veneered panel to the MDF base? Would I lay a layer of breather mesh on top of the MDF batten, followed by the panel, topped with another layer of breather mesh?
Any suggestions of thoughts about what I may be doing wrong or what I could try would be greatly appreciated. My “trial and error” pile has grown to large for my comfort.
Thanks everyone!
Eric
Replies
http://www.vacupress.com/index.htm
Been to the veneering forums? The answer might already be there.
You must apply the face veneer and backer at the same time. The water in the PVA will bow your panel every time. By completing both at the same time you balance the moisture abosorbed by the substrate on both faces so the panel does not curve. Sometimes you might get away veneering one side only if you use a Urea Formaldehyde, but thats still a bad idea.
To stop the panels from adhering to the platten, use cauls or plastic. I've used 1/4" Hardboard, Melamine, but the 1/8" shower type board (sorry cant recall its proper name) is the best. The shower board is more expensive. The top caul should not be much more than 1/8" bigger than the panel, otherwise it will break under the vacuum or if it rolls it over you can get bonding problems at the edges.
Please find a book, DVD or take a read on Joe Woodworkers site.Darryl Kiel's (Vacupress) DVD's are very useful to help you with substrates, adhesives, flattening burls/crotches and curved work should you decide to in the future.
Brad
Edited 3/13/2009 4:20 pm ET by brad805
Eric,
A couple sheets of newspaper between the project and the caul or backer board will prevent their sticking together.
Ray
I sandwich the front and back veneers on at the same time and use tileboard or stallwall you might call it - slick surface masonite, essentially, for both the front and back, and my platens are 3/4" melamine. Unibond seems to adhere to vinyl faced melamine substitutes pretty good. Oops.
I'll second the nod to Darryl Kiel. I think if you're looking to learn, his DVDs are actually pretty useful.
Real trucks dont have sparkplugs
Eric,
I'll reiterate what others have said. I always do both sides at the same time. I use 1/4" melamine top and bottom for cauls. I only allow approx. 1/4" overhang which makes it easy to size by going 1/2" over the panel size. One trick I use which helps with any possible bleed through, I spray the melamine cauls with TopCoat. That prevents any possibility of glue sticking.
I never use mesh, even on curves, unless I have a compound curve or something similar in difficulty. The time to use the mesh is when you're using the bag without a platen and need to get air to the nipple.
Earl
You should veneer both sides of the panel at the same time to eliminate the cupping problem.
I cut my panels a bit oversisized by about a 1/2" to 1" in length and width and make the cauls the same size. The edges of the top caul get eased to protect the bag. The veneer gets cut slightly larger. When the bag tightens, it bends or breaks the veneer down over the edge of the bottom caul, keeping the glue off of it. If the cauls do stick, it will only be slightly adhered at the edge and easy to break apart.
The edge of the panel then gets cleaned up by jointer, edge sander, utility knife, or whatever is appropriate or available, and the panel gets cut to its final dimensions.
dmd
Both side at same time.
What is leading you to do it one side at a time? It is faster to prepare the sandwich and vacuum it once.
If you're having problems keeping the veneer from sliding around, use multiple pieces of blue painters tape - place a strip maybe as close as every six inches. Wrap it around the sandwich of veneers and substrate to keep the veneers from moving. Then put it into the vacuum bag.
Greg
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Exo 35:30-35
Eric,
If you are using PVA or PRG (which is mixed with water), you should do both sides at one time. You should consider using wax paper and a platten on top and then the mesh as well.
However, 45 minutes may be a short enough time to pull the panel out and place the back veneer on and rebag the thing and perhaps have the panel balance out. The PVA or PRG is still reasonably elastic in 45 minutes that the creep will allow the face veneer to relax--but I would leave the assembly in the bag the second pass longer.
I typically use epoxy for veneering panels. I often only do one side of thicker shop sawn veneer on top of ply. But I do leave the assembly in the bag long enough for the epoxy to cure in those circumstances. When I have used PRG, I allow for time to cure.
Take care, Mike
The only thing I have to add to the excellent advice you've gotten already is that a warming (electric) blanket will help the glue dry faster, and allow you to remove the panel from the bag quicker. I always do both sides at once, and use either Unibond or plastic resin glue, depending on what I have in the shop at the time.
Jeff
As others have said, it is usually better to veneer both side at the same time. I try to do that. But sometimes I do one side at a time, and still get flat panels. The second pressing must be done immediately upon removing the first from the bag. And I get good results with pva glues... regular titebond II. I like Unibond for its stability, but pva is faster and healthier, I think.
That said.... something else may be wrong with your setup. You didn't fully describe your platten/bag/support system so there may be a problem there. If your support platten isn't flat, you cannot expect your panels to be flat either. I have a 4x8 foot torsion box that serves as a support. The box was made to be as flat as I could possibly make it. And indeed, there is very little deviation in its surface, and it is very stiff. This is placed on stout sawhorses. The bag with its internal platten is laid on top of the torsion box so that it lays flat.
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