Darryl Keil Last Activity 2025-09-09 11:09 AM
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Jim Clark

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Joined: 2007-04-02
Location: Phoenix, AZ

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Subject : curved desk pedestal crotch mahogany, help for a newbie
Posted : 2007-04-02 6:47 PM
Post #33725
I have a pedestal for the end of a peninsula (double sided) desk. The pedestal has an eliptical (convex) shape that I was planning to cover with a nice crotch mahogany veneer. I have never done a veneer before (except formica with contact cement), I don't have a vacuum press. From reading some posts on this forum, it looks like my first attempt might well be a failure.... Any tips you could give would be greatly appreciated.

The pedestal is roughly 30" high, 42" wide and about 10 inches deep. The length along the curve is almost exactly 48inches. I looked into a vacuum press at Woodcraft and it was about $350, but now it looks like I'm going to have to bite the bullet and get one. Any suggestions? Since the whole pedestal would have to fit in the vacuum bag, I would need a fairly big bag (see dimensions above). Are there any vacuum press considerations to applying a vaneer to such a curved surface?

The curved portion of the pedestal is made from 2 layers of 3/8" bendable plywood and is already built. The surface seems very soft and there are quite a few minor cracks in the surface that I was planning on filling and sanding smooth before veneering. Would this be ok? If the surface of the plywood is too soft (it dent's with a fingernail)is there some way to harden this surface prior to applying the glue?

I'm finishing the project with sprayed on lacquer (Deft hi-gloss), over a water-based wood dye. What glue would be best for this finishing system? I have read about "bleed-thru" on highly figured veneers, and want to avoid this to get 1st or 2nd time success on this glue up.

What other stuff am I missing? Maybe so much that I should just go away and read a good book on this.... What book(s) could you recommend?


 
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Don Stephan

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Subject : RE: curved desk pedestal crotch mahogany, help for a newbie
Posted : 2007-04-03 8:34 AM
Post #33726 - In reply to #33725
As I read through your post, I think you are seeing that the project you are describing would ideally follow quite a few "work-up" projects to gain experience and comfort working with veneer.

There's not a good book I have found for vacuum veneering, but much of the relevant info is contained in old discussions of this forum. It WILL take hours and hours, but the content is a great starting point. The other great references for vacuum veneering are the videos by Darryl Keil at Vacuum Pressing Systems and the videos by Paul Schurch (I'm excited to learn his new video is out this month).

There's no substitute for experience, and the first issue is whether you want to develop expertise working with veneer. If so, I'd highly recommend a call to Vacuum Pressing Systems to discuss what capabilities you'd like to have and what those would require in terms of a bag and vacuum generation. If this is a one-time effort, sub the veneering out.

Crotch mahogany is a difficult veneer to work, with even on the flat. It often needs flattening, it may need crossbanding, ... Your pedestal likely has seams, which are more complicated than on the flat. A vacuum will quickly crush a non-flat surface if not properly supported. I don't mean to discourage you or anyone else from working with veneer - it is challenging but offers great design capabilities. However, this does not sound like a project for a novice.


 
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Darryl Keil

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Subject : RE: curved desk pedestal crotch mahogany, help for a newbie
Posted : 2007-04-03 6:40 PM
Post #33728 - In reply to #33725
Jim,

Whenever I hear or talk with someone who is attempting a first time veneering project I like to let the person know on a scale of 1 to 10 how difficult there project is likely to be. I think of yours around a 7 to 8 which is pretty tough for a first project. First, you want to use mahogany crotch which can be a very ornery veneer to work with as Don suggested. Second you want to veneer on a oval which can also be a difficult challenge.

As far as the crotch goes I would strongly suggest making a two ply which means pressing the crotch to another backer veneer with the grain running 90 degrees to the crotch. This will stabilize the crotch and help mitigate the roughness in the bending ply. Be aware that you will get bleed through on the crotch, no way to stop that. You can scrape and sand the bleed through off and you'll be just fine.

In regards to your oval pedestal, which I'm guessing is a half oval,(its not really clear from your post),it must be well braced. If the pedestal is not properly supported vacuum pressure will collapse it under full vacuum. Something to consider. Rule is, full ribs every 6" on center with two layers of 3/8" bending ply.

There's a lot more to this than can be conveyed in writing but this should give you some ideas.

Sincerely
Darryl Keil


 
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Jim Clark

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Location: Phoenix, AZ

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Subject : RE: curved desk pedestal crotch mahogany, help for a newbie
Posted : 2007-04-07 8:58 PM
Post #33749 - In reply to #33728
Thanks Don & Darryl! Your advice is greatly appreciated.

In regards to the backer veneer for the mahogany crotch, what should I use? A cheaper paper-backed mahogany veneer, or will some other species do as well or better? Should I glue the veneers together 1st then to the pedestal or all in one step (the latter makes more sense to me since it seems it would become stiff and brittle if I glued them 1st).

Thanks for the heads up on crushing my pedestal in the vacuum bag. I hadn't "done the math" on that to realize how much force it would be subjected to. Fortunately, I can retrofit more ribs to the pedestal (1/2 ellipse) to shore it up for the veneering.

I'm a little confused about the "bleed-thru". I can imagine the convoluted grain structure allowing glue to pass thru to the front side. Is that what's happening? If so, is it really possible to get it clean enough after the glue cures to not effect the staining process? I hope this is what you meant about being "fine" after scraping and sanding.

I have a friend who's a custome guitar builder that's going to help me with the mechanics of the vacuum pressing. Fortunately, the only time pressure is what I put on myself.

Thanks again for the help. Maybe I'll post some pictures to show my progress.

Jim


 
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Darryl Keil

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Subject : RE: curved desk pedestal crotch mahogany, help for a newbie
Posted : 2007-04-08 3:43 PM
Post #33753 - In reply to #33749
Jim,

For a pedestal base the kind of backer veneer you use really doesn't matter much. Use whatever you have on hand.

I would be inclined to make up the two ply first and then glue it to the formed pedestal. Of course this depends on how tight your tightest radius is. You did not give any dimensions so I cant give specific advise on the capacity of the two ply to bend around your pedestal. If nothing else, glue up the two ply in the morning and press it to the pedestal late in the same day, before the glue has completely cured but enough to hold the bond of the two ply together. At this stage the two ply will have more flex than the next day.

There is no way to stop bleed through on mahogany crotch, so yes, if you scrape and sand thoroughly you will have no staining issues. Glue up a scrap of the crotch so you can have a test piece to run the scraping, sanding, and staining process on.

Sincerely
Darryl Keil


 
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Jim Clark

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Subject : RE: curved desk pedestal crotch mahogany, help for a newbie
Posted : 2007-04-25 4:07 PM
Post #33790 - In reply to #33753
Thanks again. I was reading a book a the local Woodcraft store and it mentioned dying the veneer before the glue-up to reduce/avoid problems associated with bleed-thru and staining. Would you recommend this? I am using a water-based wood dye (not stain). If this is a good idea, should I stain before or after the flattening process? I also worry about the flattening solution impeding dye penetration. Any thoughts?


 
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Don Stephan

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Joined: 2003-07-18
Location: Cincinnati, Ohio

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Subject : RE: curved desk pedestal crotch mahogany, help for a newbie
Posted : 2007-04-29 9:33 AM
Post #33796 - In reply to #33790
Give it a test try! Sounds like it'd be a mess with dye getting everywhere. Don't know if it would cause buckling and curling in the veneer to re-wet after flattening.

I've used water based dye once or twice after vacuum pressing and not had any problems.


 
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Don Stephan

Posts: 825

Joined: 2003-07-18
Location: Cincinnati, Ohio

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Subject : RE: curved desk pedestal crotch mahogany, help for a newbie
Posted : 2007-04-08 4:02 PM
Post #33754 - In reply to #33749
The following are notes I have copied from forum discussion threads on making two-ply veneer.

"The three instances when two ply veneer is commonly used are: when the face veneer, like crotch mahogany, has a strong tendency to check or crack; if the veneer is too fragile to work with; and when the substrate is a curved surface not perfectly flat (such as bending ply).

"Backer grade mahogany veneer is an excellent material for the back side of two ply veneer, because backer mahogany is available in wider sheets and is extremely stable.

"The show side of the primary veneer is taped with solid veneer tape. The back side of the backer veneer (that will be glued to the substrate) is taped with 3 hole veneer tape to allow more glue contact between the substrate and the back of the backer veneer. The primary and backer veneers are glued at right angles to each other.

"Apply the adhesive to the front side of the backer veneer. Lay on the bottom caul. Position the primary veneer on the backer veneer. Immediately cover with the top caul, place in the bag and draw the vacuum. As soon as the primary veneer contacts the adhesive it can begin absorbing moisture and buckling.

"If the substrate is thin, consider applying a two ply to both sides to minimize warping. The back side two ply could be simply two layers of backer mahogany at right angles to each other.

"If the two ply was made using a rigid glue like urea resin, the smallest radius it could later be bent to is about 10”. If the two ply is applied to the curved substrate the same day (before the urea resin has fully cured) it can be bent to a tighter radius."

As always, trial and experimentation are keys to success.

Excellent general resources on working with veneer and vacuum pressing are "Decorative Veneering" by Paul Schurch www.schurchwoodwork.com and "Working With Veneer" by Darryl Keil www.vacupress.com. An excellent resource for working with curved surfaces is "Working in a Vacuum" also by Darryl Keil www.vacupress.com. I highly recommend all three.
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