Saturday, October 15, 2016

A Ming-Inspired Cabinet (74)

Both bonnet tops are now ready for finish:

I'll save final assembly until I have applied finish to the parts individually. I'm also working on a decorative element for the front of the bonnet riser panel. More on that at a later date.

Next up is the second-to-last construction task on these cabinets, namely the rear demountable panels. Perhaps it is worth explaining some reasons as to why I am making the panels demountable, as it is hardly the easiest way to fit back panels to a cabinet. After all, once the cabinets are full, you can hardly see the back panels. Perhaps I should just nail some rough sawn boards on, planed only on the face that shows? Perhaps a secondary wood should be used, as the client is unlikely to have any reason to directly specify bubinga back panels. Plywood is certainly a common choice for back panels.

Well, while there are certainly virtues to economy and frugality, virtues that might guide my endeavors in other spheres of activity, that's not what this project is about. The argument that because something isn't directly obvious it should not be given the same elaboration as other elements has never carried any weight with me.

I'm making the back panels out of quartersawn bubinga, and placing them in separate frames, also of  bubinga. These frames will be attached to the cabinet such that their removal will be a simple affair at any point in the future. Why does this approach offer an advantage? Well, consider for a moment if your task was to refinish the cabinets. Would it be easier to refinish the back panels in situ, or with them removed and laid flat? If the panels or their frames were to get damaged, the fact that the units can be easily removed means they repairs can be enacted, without any recourse to surgery on the main cabinet parts. Sure it is extra work to prepare cabinet back in this manner, but I feel it is well worth it - and I'd like to think that it let's the craftsperson who fixes this cabinet at some later point when I am long gone that I was thinking of him/her when I built it.

The panels were prepared from rough stock months ago, first down to 0.5" thickness, then allowed to sit for 3 months, and then taken further down to 0.375" thickness, and then allowed to sit a further three months. They have remained very flat though that process, so I'm confident they will continue to behave that was on into the future - even more so, as I have reinforced their backs with three dovetailed battens each:

At this juncture, the battens are little more than roughed out and only started in the fitting process.

A closer look:

The strategy of stiffening thin panels with dovetailed battens has a long history and is very commonly seen in the best Chinese classical furniture. It's a sign of quality work, even to the point that it became a copied design element, sans sliding dovetail (unfortunately) in later works, both in China and Japan.

Solid hardwoods are heavy, and therefore it is a good plan to keep panels thin wherever possible. Thick slabs of wood, like tabletops, say, can also be reinforced with dovetail battens, however there is a sort of cascade effect there which makes them a less desirable solution in many instances. Why? Well, for a batten to have a significant role in keeping a panel flat, it needs to be stiffer then the panel, which means significantly deeper in section, or, if the panel is a softer and weaker wood, it could be made simply out of a harder and stiffer material. I'm not sure where the precise line might be, but I would imagine that a batten which is two times as deep as the panel is a reasonable starting point. The deeper the better. With a thick table top however, say 1.5 or 2", then you would quickly end up with battens that were anywhere from 3~4" tall, or more, and this might be detrimental to design in other respects, practical or aesthetic.

Making the panels thin keeps them light, and appropriately sized battens keep them flat. Trenching crosswise breaks up the run of the grain, giving the panel decreased ability to warp or bow over time.

There is another major advantage to frame and panel construction with dovetailed battens, besides the obvious fact that it allows a wide panel movement within a framework and keeps panel flat. The connection of battens to the panel with sliding dovetails, and then battens to frame with mortise and tenoned joinery, allows the frame to borrow shear resistance from the panel itself. This is a major boon to door construction, and I will be employing it on the bifold doors for this cabinet.

With the panel backs, the shear strength aspect is relatively unimportant since there are no shear loads on the panels, however I thought I would make mention of it as a side benefit all the same.

I cut the sliding dovetails without taper, employing a jig along with router and guide bush to make the dovetail grooves, and then router table to make the dovetail males.

Even with careful work, sometimes a bit of debris gets between the guide bush and template, or if I decreased side pressure for a moment while cutting, certain parts of the groove can end up with niggling areas of interference. For that, there is a handy Japanese plane called a hifu-kura-ganna to make slight corrections:

Another view:

This plane can be a little tedious to adjust, but it does the job for sure:

The first of the wide (middle) panels with battens all fitted:

Another view -the batten has been planed and chamfers and tenoned, it might be noted:

 A batten is properly fitted when it is a snug fit and yet no so tight as to cause the thin panel to bow:

 At this juncture I have completed the work on the battens and panels for both cabinets:

As for the cabinet frame members, they are cut to width, thickness and length, and I have commenced layout for the joinery. I'll detail the work on those pieces in the next post.

Thanks for visiting the Carpentry Way. Oh, and by the way, I was invited recently by the Woodworker's Guild of America to submit this blog for an awards contest. I'm certainly not going to do that myself, however if you do like what you read here and would be willing to vote your support, then please take a moment and click on this link to register your vote for favorite woodworking blog - even if it isn't this one. And if I win, I get a million dollars or something like that. Well, maybe something less grand - possibly, at a minimum, wider exposure for this blog on the world wide web. Seems like that would be a good thing.