I’ve run across something I’ve not done before…veneering a curved formed. I’m familiar with veneering flat surfaces and thought that the curved surface would prove only a little more difficult. I’m making a hall table with a curved apron. I’ve laminated four pieces of 3/4″ MDF together and have shaped it to my desired outer radius. I’ve been struggling in figuring out how to put it into my veneer press bag (4’x4′)…and while the apron goes in the bag when I do dry runs and suck the air out…the bag tends to cooperate not at all and wrinkle and crease over itself not putting even pressure where I need it most.
Wondering if anybody has any thoughts on the following idea: Glue my curved surface, lay the veneer and secure it with pieces of veneer tape where I want it…for pressure I thought about using a piece of 1/8″ plexi glass slightly wider than my form and use band clamps to distribute the pressure…? Like I said, I’m new to veneering curved surfaces and realize this probably doesn’t give my the same pressure as my press bag but….
I have included a picture of the apron seeing as sometimes my descriptions aren’t the best. The inside section of the apron will eventually be cut away, but when I glued the form up I figured I’d leave the waste on the inside so the pressure from the bag wouldn’t crush the apron.
Any thoughts or suggestions would be greatly appreciated…just for visuals I’ve also included a picture of my top that I just finished for this piece.
Replies
Sheraton,
I am leery of the amount of pressure nylon band clamps can apply, esp over as large an area as a wide apron like yours. Two or better yet, three clamps, may work. Here's a picture of the arrangement I used for the apron for a "D" end dining table. Each of the holes is matched on the opposite side of the form, allowing for a short batten to span the apton's width, and a bar clamp on each side. The apron (previously laid up out of bending ply) was laid on the form then a sheet of poplar crossband then the face veneer; that was covered with newspaper, a piece of 3/8" bending plywood, then a piece of 1/4" plywood (I was trying to spread the clamp pressure), then the batten. I started clamping in the center, and worked toward both ends alternately.
I used every clamp I had, plus a few from the neighbor. In addition to the curved apron shown (the belly of the "D"), I veneered two sections that were curved for a portion of their length, then strait for the rest (the ends- or top and bottom- of the "D") .
Ray
Sheraton, I recently had to veneer a set of curved table legs. Rather than use my vacuum press I used hide glue and a glue hammer for the curved surfaces and it worked quite well. Any areas that didn't glue up quite perfectly the first time were easily fixed with an old steam iron I keep in the shop / Al
Use your vac bag. First cut the apron to it's final curve, both inside and outside. Take the platen out of the bag, letting the fabric conform to the curved surface. You will have to use a bleeder fabric to form a path for air to escape. VacuPress sells some stuff called evacunet. It's a course plastic screen. A couple of layers of window screen may do in a pinch. You will have to use flexible cauls on both inside and outside veneers.
I would add in addition to use matching radius but much thicker oversized cauls.
BB
There is no need for matching radius, thick/oversized cauls. My method uses flexible cauls. They need only be thin things. One could use strips of plastic laminate if they were available. His flexible plexiglass will work fine. Without a fixed caul the bag conforms to the curve of the apron. There is no stress imposed that will change that curve. This method is used in the lamination of curved door arches, spiral stair handrails and stringers every day. The only difference is these applications usually employ a narrow long vac bag. There will be some awkwardness using a 4' wide bag, but it will be manageable. Or, as others have suggested, the hot hide glue method is a fine way to go.
Your right--had brain ph*rt. Thinking heavy cauls/clamps not vacuum. light stuff OK John
Hi Sheraton,
Hopefully my 2 cents will be of some help to you.
1. It sounds like the glued up MDF form that you have will eventually become your skirt apron. I made something similar using blue insulation sheets to make a form for gluing up bent laminations for a curved apron. Anyway, I would suggest making a 2-ply veneer to cover over the MDF and to stabilize the "show" veneer on the outside. With your veneer pieces cut longer than needed, try a dry run using the vacuum bag. It sounds like your form will fit in the 4' x 4' bag OK. Tape the veneer to the center of the form. You will need to "borrow" some extra hands from a helper. Pull the vacuum down slowly, use all hands to hold the veneer to the form until the bag is pulled down over the veneer and form. If this works OK, then you are set to go. What type of glue did you plan on using? I have a 4' x 8' bag so depending on the size of your form this may or may not work. I also used urea-formaldehyde glue to decrease spring-back effect after the release of the vacuum.
2. If the above does not work, then as another post suggested, use hot-hide glue and hammer veneer the apron the old fashion way.
Looks like the top is pretty cool. What type of veneer will be on the apron?
Best of luck,
Craig
http://www.paradigmfurniture.com 
Well...after several trial runs...I'm going to go old school and hot-hide glue the apron. Since I haven't done any curved piece veneering just a quick question. Is is appropriate to coat the apron with the hot-hide glue and let it "cure", then position the veneer where I want it and then heat it up again and hammer it down? Or, should I try and apply the glue and veneer it down at the same time? Seeing as it's a curved form I'm not so sure how the later would work?
I also considered the fact that if I went for the press bag route and my trials went okay theres always the chance that the real go would end in disaster...have too much time invested in that parquetry on the apron veneer to let that happen. At least with the hid glue it can be re-heated and "fixed" if need be.
Any tips or feedback as always is greatly appreciated!
Darryl Keil, http://www.vacupress.com, demonstrates vacuum pressing curved forms and veneering them in his second video, "Working in a Vacuum." It's very clear and complete, and I think would answer all your questions. I highly recommend it.
Hammer veneering with a hot iron might work well also, as long as the curves are not so sharp that the flat bottom of the iron can't make sufficient contact. (I didn't look at your pix, sorry.) As an option, you might warm the substrate first with a hair dryer or hot air gun so that the hot hide glue doesn't gel so quickly.
If you want to go the hammer veneering route, and the veneer is make up of a number of pieces (parquetry) I'd strongly suggest making a test panel and hammer veneering it first to see how much force you can apply without tearing apart the parquetry.
Good luck and hope all turns out well.
Having never done hammering with hot-hide glue on a large curved surface and parquetry veneer, I would have some serious reservations. I'm a strong believer in practice runs as Don suggests.
As I read your post about your concerns a thought came to mind. How about using liquid hide glue (the stuff made by Franklin or Titebond)? You would still be applying glue to the apron and the veneer (similar to hot hide glue). Then rather than hammering the veneer, use your vacuum bag set-up to hold and clamp the veneer in place on the apron. This removes the potential to screw-up or damage the parquetry during the hammering process. After the glue has set, if the veneer has shifted or encountered a problem you can still use a hot iron to remove the veneer and try again.
Going this route, you remove the potential to screw-up the parquetry during the hammering process while still having the open time of liquid hide glue and the reversibility.
Post pictures when its done.
Good luck,
Craig
Well, with compatibility issue of the MDF and hide glue settled, I would coat the MDF with at least one or better yet two coats of thinned down hot hide glue letting each coat dry over night, before another is applied. My experience with MDF is limited, but I know the cut faces are quite porous, so these coats would seal the wood and give you the best surface to glue on.
How is your parquetry held together? The water and heat required with hammer veneering will almost certainly remove any kind of tape. I have only built patterns in place, because the pieces shift so much from the "hammering" and the moisture does make them move too. Do you have a photo of the pattern you have made?
I have a woodworker I talk to frequently and he was sold on the vacuum press, despite my extolling the virtues of hammer veneering. He made a perfect reproduction of a Portsmouth bow front chest and decided to try hammering veneering on it. He now relegates the vacuum press to only simple flat work, as the hammering is far superior and faster.
Rob Millard
http://www.americanfederalperiod.com
Since Rob has spoken up again, I'm going to give another plug for the veneer press. And this isn't because I don't like the smell of hot animal hide.... I'm presently hammer veneering some european chestnut onto some rounded-edge panels. This is a task that vac pressing isn't well suited for but hammer veneering is. Anyway.... for your simple curved apron using the vac bag without a fixed platen is bone simple. Make a mock-up and stick it into the bag if you don't believe me. With a flexible platen over your veneer I cannot forsee any reason for shifting. Hammer veneering is great, I can't say I like doing it, but I'm still learning it. I found the learning curve on vacuum pressing to be much shorter and less steep. I've made bigger messes by far with hot hide glue than with veneer press glue. As with anything, you should practice on some non-critical material.
Sheraton:
Craig's advice is right on! My approach is hammer veneering first and vacuum bag second but that's only because I learned hammer veneering first!
Madison
I'm dedicated to hammer veneering, and this is the easiest way to go, but I'm not sure how MDF and hide glue work together.
Rob Millard
http://www.americanfederalperiod.com
For what it's worth, I've made small panels using hide glue on MDF (<2 s.f.) that have held up for over 10 years. In fact, I almost always make my veneered staining/finishing sample boards this way.
That is good to know, because I have often wondered how it would hold up.
Thanks
Rob Millard
http://www.americanfederalperiod.com
Did you take any phots of the problem? A piece like this will have to be lifted off the table far enough for the edges to bond. Is your form solid?
The caul evens out pressure, provides channels for air escape, and provides a gentle transition for the bag at the edges. It should have a radius on each edge to prevent the vacuum bag from having to attempt a 90 degree bend. Remember, it's the atmospheric pressure - the air outside the vacuum bag that provides the clamping force.
It looks like you have a fairly agressive radius on your piece. Here is a link to a setup I saw from a joewoodworker client.
http://www.joewoodworker.com/veneering/visitorspress/rozmiarek1.jpg
It appears he is using bendable plywood as cauls. Notice that the bag draws down smoothly only where needed and wrinkles far before the bottom of the form. Ideally I want a smooth bag over the veneer. Because the caul evens out the pressure, a wrinkle in the bag over the caul should not be a problem. The overall force applied would be reduced but negligibly.
Multiple wrinkles at the edges of the cauls could be a problem only if the veneer is not pulled down against the substrate.
Greg
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Exo 35:30-35
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