Thursday, February 10, 2011

Ming Inspiration (30)

Here we are at the milestone of 30 posts for this design-build. I'm making a dining table out of bubinga, a piece influenced by a Ming side table from about 1580. Previous postings in this thread are found archived to the right of the page.

I left off yesterday at the cliffhanging point, midway through the fitting of the central rail to the end aprons. These joints feature tusk tenons, stub tenons on top to resist torsion, and sword tip mitered returns on the top. These joints are the only significant revealed joinery on the entire table, so I have been fussing their fit more than is usual. These type of joints with miters on two surfaces are very easy to spoil the fitting due to an errant over cut, so I am proceeding in a rather plodding fashion. In fact, the complete fitting of these two joints spanned three mornings. Yesterday's post covered morning one, from a couple of days ago. Today I will complete the description, combining the last two mornings of fiddlin' around.

Morning two began with the sword tip looking decently close:


"Decently close" that is, if one was only looking at the sword tip. A glance further down the central rails shows that the tusk tenons shoulders are about 0.125" away. Note that pencil lines on the apron for the miter tip- I left quite a bit of material extra there. Call me paranoid if you like.

Obviously, a fair amount of material could be hacked out of there straight away, so I set up a paring block, shot a bit of camellia oil on, and started paring the miter housing:


That improved the fit at the double miter somewhat, but I was still a fair way off closing the shoulder of the joint:


I pulled it apart again, and then remembered I needed to put a pin mortise into the apron, so I went over to the hollow chisel mortiser and did that. Unusually, the pin, or komi-sen, and mortise in this case are slightly rectangular instead of square:


Back to the fitting. A little paring work later, things were getting closer:


Another bit of paring and the shoulder is within a 32nd of an inch or so:


I then did a little planing down on the apron surface to clear away a slight offset between it and the top surface of the rail:


At the other end of the central rail, the fit was creeping up on where it needed to be as well:


That's where morning two ended. A lot of people would just push through and keep working on fitting the parts, but I have learned it is better, for me at least, to set aside this exacting sort of work and deal with other stuff for the rest of the day that doesn't require such focus and patience. It's a way of taking a break from the intensity. Getting impatient with things and trying to get things done 'cause the clock is ticking sometimes leads to unfortunate mishaps that are generally to be regretted. Been there and done that.

Morning three, which was this morning, began with some slight adjustments to the shoulder lines of the central rails:


If you look closely you can see where I made a pencil mark on the side of the rail indicating the portion of the shoulder that needed a little straightening up.

Now, as things start getting into that 98%+ fitting zone, out come the feeler gauges. I find these gauges tremendously helpful- not only can I check surfaces I can't really see (like inside the joint where the sloping abutment of the tenon meets the housing), but I can get a very clear idea of where the points of interference are and thereby deal with them bit by bit:


In the picture, I am using a 0.002" feeler gauge, with the final gauge I use, 0.001" thick, above. Some woodworkers will scoff at such apparently refined measurements, but I can see the gaps perfectly well - the gauge is simple a measuring tape to tell me what size the gap is. Some prefer to measure based on, oh, plus or minus their thumb thickness, or +/- a 32nd of an inch, etc. Measuring is measuring, and if you'd rather not measure at all and hew everything with a broad axe, then more power to ya of course. I find these feeler gauges a useful tool at times.

I then gave the meeting surfaces a scraping pass of three with a wide chisel. Hopefully I'll find my card scrapers soon. Here's the 99.8% mark with the joint on one end of the table:


I think it needs one more very slight paring. The width of the central rail (the top of the 'T') is slightly oversize at this point, and will be trimmed back soon enough so the edges meet right at the miter. I'll save that very last fiddle for tomorrow morning :^)

And here is the other end of that table at a similar point:


Not sure I want to do any more to that one, but I might give it one more going over. Of course when the peg goes in it will be draw-bored a little and that will help squeeze any residual play out of the joint as well.

Let's have a look now at the through tusk tenons associated to these joints and see how they came out. First one end:


And then the other:


I have to trim them back a little and give them a clean end grain paring, something I will attend to shortly. I was pleased with the way these joints came out, though it took longer than anticipated to get to the finish line.

In tomorrow's post I'll take up the tale of the giant's arm braces once again, so please stay tuned.

Thanks for coming by today. --> on to post 31

12 comments:

  1. talk about spot on and meticulous...what is that camellia oil you splash onto your joints when paring? im guessing it softens the fibres? could water work as well? i pare my tails to fit my pins when dovetailing and always get some blow out or just not enjoying the paring process. woudl you recommend i start oiling up my surfaces when paring to fit?

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  2. Nick,

    camellia oil is sold usually for the purpose of preventing rust on Japanese tools. Oh, and as a hair oil as well, apparently favored by Sumo wrestlers. For use in paring, any light bodied oil would work pretty well, but I would say that Camellia is pretty much ideal. It doesn't soften the fibers so much as it lubricates the cut. Consider how shaving without shaving cream feels...

    I wouldn't use water to pare. First off, some woods will react to the water/iron mix, like oak, and you will get stains from the tool iron on the wood. Those stains soak in and you won't get them out. Also, of course, there is the issue of water swelling the parts slightly, which would mean that the fit might not be as good once things dried out.

    Also, for final paring, I suggest that one always take the time to go a resharpen, and when you feel the tool going slightly dull, resharpen. When in doubt, resharpen...

    ~Chris

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  3. Those are tough joints, Chris, not only having the meeting of the "sword tip" with the shoulders, but also keeping the rails square and in plane as you fit it. I don't think that it is particularly a joint that lends itself well to hand fitting, spot on off the machining might be the most desirable, or at least up to closer, but you seem to be doing a real good job with it. Lots of area on your joint as well, with the tenons and shoulders behind.

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  4. Djy,

    thanks for your comment and insights. I think that spot-on machining for that joint would have been nice to achieve, and did take place to a certain extent. However the sword tip housing, for one thing, cannot be machined so easily, at least not without CNC and a very small diameter cutter - and there would still be some chisel work needed at the apex of the point. With my use of mdf templates and a bearing guided cutter of 1/2" minimum outer diameter, it would scarcely be worth the bother to machine the sword tip housings due to the amount of later hand cutting needed.

    Complicating the fit of this joint as well was the fact that the inside surface of the apron was relieved down 0.75" and hand planed off, so I knew there would likely be some adjustments needed at the meeting of the central rail's tenon shoulders and the apron's inner face - and such was the case.

    Certain joints I tend to leave for hand-fitting, this one being such an example. That said, the tusk tenon and mortise portions were machined, at a slight interference fit, and didn't require much adjustment.

    I've developed a certain caution with sword tip junctions especially if they are likely going to be subject to scrutiny. From having done quite a few of these joints, I have adopted the approach of leaving extra material on those sword tips and then paring to fit. I do the same thing with certain timber frame joints as well, like a hip rafter landing on a beam cross over for instance. Many other joints of course do not merit this sort of attention and fussiness as they are simpler in form and fitting.

    The stub tenon on the joint described above is to help resist torsion and to help reinforce the sword tip above, in case it wasn't clear.

    Cheers,

    Chris

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  5. Hi Chris,

    I was hoping you would go over the fitting process in depth (actually I was hoping for a video of your work session, but that would be asking for too much :) And, thanks for the oil trick. I will try it on my next project and see if that improves my woodworking skills any.

    The joint looks great. But I do have a question. Do you expect the joint to retain these tolerances when the table is moved to a different climate or with change of seasons? Or, is the potential for movement minimum, perhaps?

    Thanks for the blog again. As always, it is a treat to read about this project.

    PhilM

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  6. Chris: would the oil interfere with glue later down the line?

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  7. Chris, thank you for taking us through fitting this joint and especially the description of how much time it takes you. That really helps put this joint into perspective!

    One thing I'm trying to visualize is how you get such accuracy in all the different planes of this joint -- even just the layout step. Are you using two reference faces and then measuring off from them, or are you confident enough with your milling that every face is a reference face, or are your pencil lines wide enough that fitting within that tolerance will make up for any error -- or something else?

    I'm sympathetic with djy's comment for my own work because I can only control a half-dozen shavings before I start losing the original plane that I'm starting to fit... but seems like it would be hard to create a joint like this without creeping up on the final fitting.

    Thanks again!

    jamie s

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  8. That really is an apex of woodworking skill, knowing how far you can take something with the machining and leave just enough for a nice clean result with the follow up hand work...as you describe your method. Experience is such a giver of good things with woodwork, life is too short.

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  9. PhilM,

    I might just do a video sometime, thanks for jogging my memory. You asked, "Do you expect the joint to retain these tolerances when the table is moved to a different climate or with change of seasons? Or, is the potential for movement minimum, perhaps?"

    Well, first off I have chosen a wood which doesn't move too much in service, Second, I have oriented the grain in the pieces to minimize movement. Thirdly, since mortises and tenons move in harmony with changing humidity (when tenons swell, mortises are shrinking, and vice versa), if they fit tightly at the point of construction, then they are in the best possible condition for maintaining a good fit over time. If joints are fitted poorly at construction time it means things will never fit well, regardless of humidity.

    Nick, I'm not using any glue on this table. BTW, what's 'glue'? Just kidding! If you wanted to glue it then it would be best to wipe the affected area with solvent beforehand to clean up any oil residue.

    Here's one more point I have failed to mention on the blog concerning the use of camellia oil -- normally you would use a little container with some cotton wadding in it saturated in the oil, and just dip the tip of the chisel into that pot prior to cutting. I am only spraying the oil on, which is undoubtedly a bit wasteful and messier than it should be, because I can't find my oil container at this time. I know it's somewhere, so hopefully it will turn up, otherwise I'll have to make another one.

    Jamie S, since the material is jointed and planed, I can reliably reference off of a face, and do so. That said there are innumerable tricks to achieving accuracy at each step of the process, and frankly I don't always detail that stuff here on the blog. I'll remember your interest however and try to explain more about that process in future posts.

    djy, that was most gracious of you to compliment my work! I'm not sure about any sort of apex - I'm just trying to explore the upper slopes without getting totally lost. Experience, as you say, is the best teacher.

    Thanks all for the thoughtful comments and questions - very appreciated!!

    Cheers,

    Chris

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  10. Chris,

    I can't wait to see a video of these joints! I am looking forward to it.

    BTW, thanks also for answering my questions. It's most generous of you to share your expertise with us.

    PhilM

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  11. I really like how precise you are with your fitting. The last pic of your mortices...perfect fit. I know you use a power morticer and clean up with a chisel, but the tennons,how do you cut those? this must seem a lame question concidering the complex joints you make, lol

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  12. Phil,

    well, sorry to say but not much progress on the video front...

    Ron,

    thanks for your question. I cut the tenons in this case using a shop-made jig and router, standing the stick vertically and doing the cut end-grain on.

    ~C

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