Veneer thickness

[Glynne]

I generally use bought veneer and fix to various thicknesses of mdf / ply for box tops, bases, decorative a panels etc.
However having finally got the set up of my BS350S spot on, I can now cut veneers down to about 1mm and given the amount of timber I have, I thought I might start producing some of my own. However some of the more exotic stuff I have would need to be thicker than the 1mm to allow for burrs, interlocking grain etc.

My question is what is likely to be the maximum thickness I can use as a veneer before I have to start worrying about movement?

I appreciate that there is no absolute definitve answer given the many variables in species, dryness, environment etc. but I'm guessing there must be a rule of thumb up to which you're reasonably safe in assuming there will be no or minimal movement.

As an addendum, I have previously used normal Titebond and Titebond cold press without any problems of creep (but my panel edges are normally captured within the overall construction) but I'm thinking if I start to use thicker veneers I probably should move to a different glue such as Cascamite?

 

[stuartpaul]

Glynne,

I've used 3 mm oak burr veneer on a 12 mm plywood base with no problems. Obviously a balancing veneer was used.

Glue was cascamite.

 

[custard]

My question is what is likely to be the maximum thickness I can use as a veneer before I have to start worrying about movement?

I too cut most of my own veneers and this is a question I continue to wrestle with.

To clarify though, when you say "movement" I'm talking about micro-cracking, when the bottom or glued surface of the veneer is prevented from shrinking and expanding across the grain by the substrate, but the top or show surface obviously isn't held rigid. At some point of increasing veneer thickness the top surface of the veneer will start to move differently from the bottom surface, might take a few months but minute little fractures and fissures will open up along the grain and it looks nasty.

With a burr veneer the wild grain pattern means there's rarely much width across the grain, so you can generally get away with a thicker veneer, indeed you normally need a thicker veneer to provide enough structural integrity for the burr to be able to withstand handling.

But for normal, reasonably straight grained veneers this is a real issue. Cutting your own veneers it's tempting to make them very thick to give the option of heavy sanding and re-finishing in the future, but you'll often regret it if you do. American woodworkers often talk about 1/16" as being the maximum thickness, so 1.5mm. John Makepiece ran an exhaustive series of tests with Hamish Low and they concluded 1.2mm was the safe maximum. Many British craftsmen I've spoken to aim for 1.0mm. Having said that I once had a few exceptionally rare and beautiful boards of rippled Oak, I reckoned that being quarter sawn and with Oak's very coarse and open grain I could get away with 2.0 mm veneers, and sure enough ten years later they're as good as the day they were laid. However, I ran my own experiments on some crown cut Pearwood (with very tight grain) and within six months using 1.8 mm there was clear micro-cracking along the grain, but the 1.2mm veneers were unaffected.

Another possibility is "cladding" rather than "veneering", where you lay a veneer on a ground of solid wood but with the grain of the veneer and the ground all running in the same direction. You might do this to eek out some particularly fine boards that you have. Then you can go much thicker with the veneer because the ground and veneer will both shrink and swell together, I'll sometimes clad Oak with something special like Rippled Black Walnut for say the under-carriage and legs of a table for example, where no end grain is visible and I want to stretch my precious stocks of an irreplaceable timber that bit further.

Cascamite is a good choice for vac bag veneering as long as you've got the time to keep the pump running and the bag occupied for 18 to 24 hours. I often use a slightly different UF adhesive (Cascamite is a UF) such as Bordens or F120

http://www.airpress.co.uk/295-f120-urea ... kg1kg.html

These are liquid UF glues and come with a choice of fast or slow hardeners, so I can use a fast hardener with a heated blanket on top of the vac bag and the job's done in a couple of hours.

Incidentally, you can't usually lay a veneer that's straight off the bandsaw on both faces as the rough saw cuts will telegraph through the veneer and look terrible after a few months. i bandsaw my veneers a few tenths over thickness and bring them to final thickness with a drum sander, but at a pinch you could run a board through a planer thicknesser, bandsaw off a veneer, lay the smooth face down, then sand the rough face afterwards. The problem with this strategy is that you can't really do book matched veneers this way (and once you get into veneering it won't be long before you'll want to book match).

One final point, with thicker saw cut veneers at say 1.0mm thick, you really should edge glue the veneers with PVA when jointing them together and before laying them. I know some furniture makers who even edge glue 0.6mm thick commercial veneers. That's optional, but for 1.0mm plus thick veneers edge gluing is mandatory. It sounds hard but it's really not, you shoot the edges as normal, then apply tape to the joint on the glue side. Open up the joint like a hinge and run a minute bead of PVA to the joint, then close it up, wipe away squeeze out, and apply tape on the face side. After half an hour remove the tape from the glue side and you're ready to lay the veneer. After just a bit of practise you'll be laying veneers with totally invisible glue lines, which is the standard you should aim for.

Good luck!

 

[Baldyhippy]

Fantastic post Custard. Thank you.

 

[Glynne]

Thank you for the really detailed reply Custard, it covered my queries and a lot more.
I went on Peter Sefton's veneering course last year so I have a good basic understanding of using commercial veneers of 0.6 / 0.7mm thickness and indeed we edge glued these as a matter of course.
I don't really do work of sufficient size to warrant a bag press but I have to admit I was tempted after seeing one in use at Peter's.
In terms of movement, I was probably thinking more of the veneer trying to move against the substrate rather than within itself as you described and so it is really helpful to understand that issue as well. My thoughts were that the veneer may either pull away from the substrate or cause the substrate to bow (although balancing should reduce any bowing).
I tend to use MDF as a substrate and so I'm not sure how this might affect "cladding" as you describe as the substrate will have no movement and I'm guessing more likely to incur cracking and fissures with thicker veneers?
As I mentioned, my veneering at the moment tends to be smallish panels (A4 size) but I'm probably looking to move onto complete boxes in the future and so your advice is really appreciated.
Many thanks for taking the time for such comprehensive reply.
Glynne

 

[custard]

In terms of movement, I was probably thinking more of the veneer trying to move against the substrate

Sorry Glynne, I misunderstood.

There's no problems with a thicker, saw cut veneer warping any reasonably thick substrate...as long as the backing veneer is also a similar saw cut veneer. By and large you shouldn't back a saw cut veneer with a thin commercial veneer, there are tiny exceptions to this rule where the ground is massively thick (as occasionally happens in contemporary furniture on components like aprons that are flushed off to legs inside and out) but for all practical purposes the backing and face veneers should be similar.

Interesting that Peter Sefton recommends edge gluing on 0.6mm veneers (he really is an excellent craftsman), there's no doubt that's the best practise, but unfortunately it's not that common. You can see the results on some lower grade veneering, the joint between two leaves of veneer shrinks on the face side as I previously described, this opens up a tiny fissure along the joint which then gets full of grime, so after a year or two there's a tiny black pin stripe running along the veneer joint. Quality edge glued veneer work (or traditional scotch glued veneer) holds up indefinitely and invisibly.

Good luck!

 

[Glynne]

Thanks again Custard.
If not the same veneer, I always back with a veneer of the same thickness but with a very thin substrate (say 2mm MDF) you have to be a bit sharpish to avoid any bowing before you get the second side laid - or at least I do when using Titebond.
Yes Peter is excellent as a craftsman and in terms of best practice and can explain how things were done traditionally as well as to how utilise modern techniques and products without compromising quality.