KevM":2rz24j07 said:
I can't comment from personal experience, but Bob Flexner ... dismissed this 'usual rule' as a myth.
I can though. I don't think Mr Flexner is wrong on all counts. I do think he over states some factors and omits discussing others.
His emphasis on only using kiln dried timber I think is overplayed. There's a lot of good internal furniture made with air dried wood. The key I believe is adequate construction rather than kiln drying. For instance large pedestal tables may be polished only on the show surface and edges, but the underside is usually heavily reinforced with cross bracing. Standard four legged table constructions rely on the rails to hold the tops flat (and sometimes cross bracing). Drawer fronts that are only polished on the front are usually fairly small and the corner joinery is usually sufficient to hold the front flat. These strategies don't always work, but the cause of any warping could be a range of factors, e.g., wood that's either too dry or too wet for the final place in service, pieces moved from a very dry atmosphere to a much damper one or vice versa, inappropriate grain pattern for the job, e.g., radially sawn wood might have been a better choice than tangentially sawn, etc.
Where he discusses cabinets, it's true there are many examples where only the show faces are polished, but he doesn't explore the fact that a cabinet interior frequently creates its own relatively stable micro climate, more stable than the exterior, i.e., changes in external RH are more volatile than changes in the cabinet's interior RH because doors and drawers may not be opened frequently.
In addition, some of the traditional finishes, still in use, offer little or no barrier to water vapour. Into this category fall the pure oils and waxes, so finishing only one side wouldn't much affect adsorption and desorption of water vapour into and out of the wood on either the polished side or unpolished side, assuming more or less equal exposure to atmospheric RH variations. Film finishes are more resistant to water vapour, although not impervious, and I have quite frequently seen panels finished with this finish type on just one side cup one way or another, usually concave on the polished side. Finishes such as shellac, varnishes, lacquers and poured epoxy resins fall into this group.
I believe there are more factors in play than Mr Flexner discusses. This is just my opinion of course, but it is based upon quite a number of years experience in the furniture profession. Other furniture makers may have a different take. I do think rafezetter needs to consider his flatness maintaining options carefully if his plan is to pour a thick epoxy finish on just one side of panels that go to make up his desk. Slainte.
