curved desks: off topic of Bot

[loriny]

I am in the process of bidding a job for a national historic site. Part of the work is 2 curved front reception desks. They call for doulde layer of 13mm(1/2) plywood with birch veneer. The tightest radius appears to be 57". My plan would be to bend and screw 1 sheet 1/2 plywood to forms cut on Bot. Then glue and screw from the back a piece of prefinished plywood as all the rest of the parts would be PF(no trying to match colors this way) Does this sound possible or would I have to bend and then laminate a veneer?
I can try bend some I have on hand but if any one has done this before I would appreciate any advice.
Lorin

[thewoodcrafter]

Lorin,

You will not be able to bend plywood with a glued-on veneer or laminate.
It will not bend, it will brake.
You will need some type of bender board, either Kerf Core or Wiggle Board.
Then laminate your skin.
I have done this several times and I like using 3 layers Kerf Core 1/4".
Use spray contact cement in thoughs pressurized cylinders.
Any imperfections need to be filled with bondo of they will show through your skin.

Good luck.

[dlcw]

Concur with Roger on this.

Build a frame and then attach bendable plywood to it to the thickness you want. Then apply your veneer onto that. Make sure that the final substrate that will take the veneer is perfectly smooth and has no imperfections or it will show through in the veneer. The church mantel in the pictures used $500/sheet of Indian Rosewood veneer so mistakes were not an option. The results were excellent.

[dlcw]

Another thing on this topic, you can use the Shopbot to cut all your parts that make your frame. Saves a lot of time and is very accurate.

[loriny]

Thank you. That had been my worry that the veneer would crack. I would cut the frame parts on the router, but for now I guess I will take a shot at bidding this one.
Beautiful work, both of you.
Lorin

[bleeth]

Hey Roger: I just delivered a couple of reception desks that look just like the pod in yoiur picture! Did you do the S-Bar too?

When laminating 4 x 8 veneer around a curve too tight to use phenolic back product I use a contact like adhesive made for paper back veneer. Contact cement can cause problems when finishing. The outgassing from the sealer can get to the contact cement and cause bubbles.

[loriny]

What do you mean by contact like adhesive?
Lorin

[thewoodcrafter]

Hi Dave,

There were 2 of those I did for a Courtyard Marriott around the end of 2008.
I did the S -bar too. It was a really challenging project.
All of this was laminate.
But I have done wood veneer jobs too.
I have prefinished and post finished the veneer and never had any problems either way with the contact cement bubbling. I would think you really need to soak the veneer with the finish to get any problems. I use a fast drying sealer first then the finish, no problems.

[bleeth]

The reception pods are walnut veneer on the one we did. Focal Wall and Go-Board are qrtrd ash. Everything else was lam.

There is a specific "veneer adhesive" that is available at some specialty suppliers. I think Woodworkers store and Rockler carry it. I get it from a wood store up the street that only has branches here and New York. It acts like contact cement but is made to have no reaction to styrene gassing. Expensive but I have found it worth it. Most of the finishers around here have a heavy hand and don't like to let it cure long enough before second and top. I have never had bubbling when I finish it but I don't do that inhouse anymore.

[waynelocke]

I have made curved reception desks by making curved panels in a vacuum bag using 1/8" ply and 3/8" bending ply for the core. You could use Kerfcore like someone mentioned and veneer it flat and then bend it around the forms.

Thirty+ years ago I worked in a shop and made more than a few curved pieces. We used hardwood ply, walnut, oak, whatever and kerfed the sheets on a tablesaw every 1/8". Worked beautifully but was a real Zen process.

I am not a fan of paperbacked veneer and similar products because the veneer is so thin and I believe results in a much inferior product to regular veneer. The paper backed is much more fragile and unrepairable. If you plan on using paper backed I would check the specs and make sure it will be acceptable.

[loriny]

Wayne: When kerfing did you almost cut through or how deep did you go? It seems the veneer might rip if not almost to it. If I was to do this I might just let the bot cut aeries of 1/8 wide grooves while I do other things. Just thinking of doing it on the tablesaw bores me and I like to make the bot earn its keep.
Lorin

[wberminio]

I get my paperbacked veneer from www.oakwoodveneer.com
They carry a thicker backed veneer that helps eliminate any problems with bubbles.I believe they actually call it "bubble free".
I have laid up my own veneers and vacuum pressed.But who is willing to pay for the extra work involved?
Never had an issue with contact.I use H2O based Contact


Erminio

[wberminio]

Lorin

I have used my Bot to cut the kerfs.It works very well.You need to cut upto

the veneer.Spacing is also critical.I would do some test runs to determine depth and spacing.All material is a bit different.
Let me know if you want more info.

Erminio

[waynelocke]

We kerfed just into the last ply of the core, about 1/8" from the face.

We always left 1/8" between kerfs and you could wrap around most anything without having facets on the front. The calculation for kerf spacing that you can find in books and other sources never really worked very well for me on plywood. 1/8" kerf and 1/8" tongue and you can wrap most anything in any direction.

You would need a vacuum table on the bot and you might have a problem with tearing out some of the tongues but you could probably do it

[Gary Campbell]

Personally I wouldn't even consider cutting 5/8 deep by 1/8 wide kerfs on the SB. The stepdown and/or cutspeed requirements mean that it would take forever. (to me!) Kerfing plywood is a workaround for not having the proper materials. OK on a construction site for rough frames, but not in a cabinet shop environment.

Make a radius form on the Bot like Don shows above and use as many layers of "wiggle" or bending ply as required by the designer. A quick coat of bondo where needed... done in 10 minutes and is as smooth as you can make it. Ready for veneer.

[waynelocke]

I have met Gary and seen his website and certainly respect his knowledge and work but kerfing as I am describing it is anything but a job site process for rough work. It requires a good tablesaw with large side and outfeed tables, a very good sawblade and a certain amount of skill and care. I haven't used this process on curved work in decades but done right with high quality hardwood plywood it can yield top notch results.

I also disagree with Gary on substrates. I would be terrified to veneer straight onto bending ply because, at least around here, most of it is a little rough. Adding bondo would seem to me to make it worse. Any imperfections in the substrate is more than likely to sooner rather than later telegraph through the face veneer. I'm not sure how Gary would veneer it so he probably allows for the core imperfections but that would be my concern.

I may be a bit cranky today because I just started to, at least, replace the head gasket on my beloved Miata.

If I were building this I would use bending ply with a layer of 1/8"mdf on both sides and veneer on top of that on both sides. The mdf creates a surface that can be veneered in any direction, is smooth and glueable. I would also use a catalyst and resin glue on a form in a vacuum bag.

I would not use the paper backed and would, in fact, use that as a selling point and make sure that I speced raw veneer in my bid. I would emphasize to the client that the paper backed offers only a small savings to deliver a vastly inferior product. For what is probably a high traffic area the paper backed and such will simply not hold up as well. The only benefit seems to be that it is cheap compared to using raw flitch cut veneer, however, any damage during construction, delivery, installation or use is virtually unrepairable which makes the savings evaporate. Sorry but the paper back always elicits a rant from me. I once was at a seminar where a manufacturer's rep was explaining that their paper backed veneer could be used with contact cement on the top of large conference tables. He backed down when challenged by several participants including me.

I'm sure there are also other ways to approach this job. It's what I like about woodworking there are almost always more a few ways to skin a cat and ofter it comes down to whether it is Monday afternoon orTuesday morning.

[Gary Campbell]

Wayne...
I didnt mean to trip your trigger, especially when you have grease on your hands! My comments are not meant to cast doubt on your methods as much as todays materials. Back in the day, I too would not hesitate to kerf up a sheet of plywood to do this. With the majority of plywood available these days it is an exercise in futility.

We have a 9' slider and a good assortment of blades, have tried this a number of times in the last few years, with results that vary from mediocre to poor. Segments seem to show due to core variations and have even had some that looked good split. Thats the reason we switched to the "bendy" ply.

The surface of the bendy is, as you mention, not very smooth and porous. Thats the reason we slick it out with bondo. This yields a very nice surface that takes most glues well. The 2 parts very well. The quick drying time gets the layup into the bag fast.

Like you we never use the paper backed veneer for all the reasons you mention and a few more.

Now go work on that Wankel! :D

[waynelocke]

No trigger problem. Like I said I haven't kerfed anything of any size in 30 years.

[bleeth]

The 1/4" and 3/8 bending ply available in S Fla isn't a great quality but the 1/8 is usually much nicer. A good surface can be had by making a sheet of this your top layer before veneering. Alternately you can also add a sheet of regrind phenolic. The premanufactured various kerf-cores are a great solution, albeit a bit pricey, as well.

If the curve is not too tight I will layer up 1/4" MDF and have used 1/4" with veneer on one side prelayed up as well. The desks down below that Roger did in Cal and I did here needed a variety of solutions as a couple of the curves were just too tight for bending ply at all and we ended up making radiused hardwood corners and bent the rest.