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. Next up in this thread is post 75.

10 comments:

  1. Voted.....Hope you do well. Keep up the work Chris....I can't wait to see the finish on this figured wood....will be great (looks great with out also) Great work as always!

    ReplyDelete
    Replies
    1. Joe,

      thanks for commenting as always, and oh yeah, onward and upward to finishing these pieces!!

      ~C

      Delete
  2. Looks I should have read both posts before asking the finishing question.

    ReplyDelete
    Replies
    1. Ralph,

      I hope the answer I provided to your question from the previous post was helpful nonetheless.

      ~C

      Delete
  3. Chris,
    You speak about added shear resistance of the frame coming from the panel and battens (I would have made a cut and paste of your sentence but it doesn't work).
    I am not sure what you are pointing to. Is it preventing the rectangular frame becoming a (slanted) losange under lateral stress (or vertical stress like in an old frame and panel door) ?
    Sylvain

    ReplyDelete
    Replies
    1. Hi Sylvain,

      thanks for the question. There really isn't much difference between preventing the rectangular frame from becoming slanted under lateral stress or vertical stress, other than the direction of load. The effect would be the same. Locking the battens to the panels means that as the frame is distorted towards a lozenge shape, the load is transferred into the battens, and then, via their dovetails, into the end grain abutments of the dovetail groves of the panel. By that means, the panel would serve to resist the shear load.

      Obviously, if the load were high enough, the thin aspect ratio of the panel would mean the panel would deform outward or inward, however the shear resistance of this assembly is perfectly adequate for handling gravity loads on the frame, as would be imposed upon a side-hinged door frame.

      ~C

      Delete
  4. Even as I agree with all your construction decisions, I still struggle to get my head around how you can manage to earn a living this way. You build with Faberge aesthetics even as Faberge's clients and their tastes have long passed away.
    I've used sliding dovetails myself so I know how tricky they can be and then I rely on some compression, tapering one side so the assembly only closes tight near completion. I don't think that's remotely possible with Bubinga. I would never have thought to attempt such a joint across such a wide expanse. If I would, I would have pared down the edges of the sliding tail to make it slip across the joint, leaving only the ends appearing tight. Are these battens removable or are they in to stay permanently?
    You've not fully covered the details this back panel assembly, yet I wanted to ask whether it is intended to counter any lateral racking of the cabinet frame.

    ReplyDelete
    Replies
    1. Potomacker,

      I will accept any comparison to the products of Faberge's workshops with (incredulous) delight, however it is not true that clients on the same level of wealth as Faberges' have passed away. There are more billionaires (I would suggest that they are an appropriate comparison) today than ever, for instance, though of course, the Russian imperial family is long gone. Today, sales of luxury items such as Richard Mille watches, mega-yachts, personal jets, Bugatti Veyrons, etc., are as lively as ever it seems. Clients for really high end furniture, however, are rather thin on the ground, no doubt about it. It's not a great way to make a living most of the time, trust me.

      It's really important to me to leave behind work that, in spirit and hopefully execution, matches that of the furniture I admire the most, which is Ming Chinese imperial furniture. That's the standard I strive to meet.

      With a thin panel, fitting an un-tapered sliding dovetail is not so difficult really. If need be, for example, the panel can be flexed (bowed) to open the dovetail trench slightly to ease insertion or removal. The main point is that the batten fit tightly - if it is too tight, the panel will be bowed as a sign of that. If it is too loose, it will be obvious enough. I don't hollow the dovetail male, as that would ruin the mechanical integrity of the connection and could result in the panel not being held flat to the batten, gaps thereby resulting between the two.

      The battens on this cabinet are to be trapped within a frame which will have glued corner joints, and the battens attach to the frame with wedge tenons, so they are not intended to be removable. The battens are not, of course, glued to the panels in anyway as they are meant to allow the panels any seasonal movement that may occur.

      As to whether the panel is intended to counter any lateral racking of the carcase, well, the strict answer is 'no' in terms of intention. The panels certainly will be ABLE to counter any racking of the carcase, however, unless the glue joints holding the carcase together fail at some point, or some huge load gets applied to the corner of the cabinet (like the house falling down on it) racking is not anticipated to occur.

      ~C

      Delete
  5. Chris, I voted, good luck in the competition.

    This post is fantastic of course, and timely since we were just talking about sliding dovetails. Thank you again for your help!

    ReplyDelete
    Replies
    1. Brian,

      thanks for the comment and the vote. Good to learn that this post was useful to you.

      ~C

      Delete

All comments are moderated, so if you're planning to spam this, know now that your clicking and pasting is in vain. I do read the comments before posting, so your mission is doomed from the outset. All this time and effort trying to put your inane spam onto blogs -- is this how you want to spend your time on earth?

Please do me the courtesy of appending your name to your comment, even if posting under the 'anonymous' option. No name = deleted.

Comments NOT accepted include:

-those containing links unrelated to blog content
-spam of any kind, or ham for that matter
-did I mention that attempted spam postings will be non-starters?