the Carpentry Way: Coffee Anyone? (5)                                                          

Coffee Anyone? (5)

    
Post 5 in a build thread describing the design and construction of a coffee table having a bubinga frame and legs, a glass top, and a frame and panel shelf below. Previous posts are located in the archive section to the right of the page. If you're new here, or haven't visited in a while, here's a link to -> post 1 <- in the series to bring you up to speed.

In the last post I showed the first set of steps in processing the cuts for the joins on the table's shelf frame. Those cuts then finished out with a bunch of chisel work. First the stub tenon trenches get their sidewalls pared:


Then some clean out with the 5mm bench chisel:


Finishing with some work with the 5mm paring chisel:


Here are a couple of frame members, set down so you can see the male and female halves of the joint in relation to one another:


Note that the female half in the above photo is turned upside-down in relation to it's partner.

These two sections are then slid together, and the following few photos show the actual assembly right after the cut out work has been completed, with no adjustments to fit yet undertaken:



Here's a look at the underside of the connection as it comes closer to full engagement:


The fit was tight and my pecs got a bit of a workout sliding the parts together!

Top side again, joint halves now together fully:


There's a residual pencil line on the miter which may make it look like there's a gap at the back corner, however I think the miter will draw perfectly tight. I spot a light gap at the front corner in the above photo, but I think that will go away once the wedge clamps it together. If not, then I'll need to do a very slight paring cut with a plane. The joint halves connect so as to leave a flush top and bottom face to one another, which means I don't have to make any adjustments in that regard.

Front face - note the slight apace allowances at the end-points of the stub tenons, a gap of about 0.005":


The gap allows the miter faces to be drawn tight without bottoming out on those stub tenons.

The underside:


Then a check with the combo square to see if the joint is aligned at 45˚:


It was looking satisfactory at that point, and my somewhat fussy work in the jointing and cut out stages had produced a result that went together with no further adjustment required. That's the ideal at least, and I can't always say it works out so well, but it did this time!

This success in the miter fitting continued a while later, as I had a couple of the sub-assemblies, the end portions of the shelf frames, assembled up with the same fit quality as the first two pieces:


A few more sessions of chisel work and I had the long frame members ready to attach, and did so, forming the stretched octagonal framework of the table shelf:


Another view:


Overall, the assembly went together very well, with perhaps a very slight amount of paring needed down the line to get the cumulative miter joints to form a 'perfect' 360˚ when all together. I imagine the miters at the moment are within a tenth or two of a degree out of 45˚, so there are only a few minor pares required. That will happen when I complete the cut out of these joints - there are wedges yet to be fitted, and those will mechanically squeeze the joints up tight. I'm thinking I'll wedge up the pair of joints on each end assembly and then fit the long frame rails on, checking them for parallelism, and making any needed adjustments only on those miters between the long rails and the end sub-assemblies.

I snapped a few more photos of the frame after I had it all assembled up, so I may as well put them on the page, even if I risk a certain amount of repetition. Here's the underside of one joint:


Another view:


Front face and miter of the same joint just shown:


You can see my pencil lines are sometimes a bit off the actual cut lines. I set the pieces in jigs for the table saw and routing cuts, and this exposed some irregularities in the location of my pencil lines. I hadn't overly fussed that pencil layout, as I knew in the layout stage that I would be processing most of the primary cuts using fixing jigs - still, I was a little surprised at how far away some of the lines were from the actual cuts. It all boiled down to the first crosscut on the table saw which established a reference surface on the joint- the location of that cut, which was sighted by eye, led to the variance, along with the inevitable slight variances in the layout itself. I didn't really need to layout each stick's joinery to such an extent, but I wanted to be totally clear on which end was which and which was up and down, so I just laid them all out. In the end, the use of fixturing jigs meant that each piece was produced so as to be identical in length and location of abutment surfaces, so that is what counted, not the location of the pencil marks.

At this point the shelf frame members are mostly complete. Next, I have to make the dovetailed batten that connects the middle of the long rails to one another, and I'll be using a wedged dovetail for that connection (a slight change from what was drawn). The locking mechanisms - shachi-sen - have to be fitted to the corner miters yet, and then the dado for the panel will be cut all around. Finally, there are the housed joints where the table legs connect, and the moulding of the front faces of the frame to be dealt with. I now have the custom shaper cutters on hand for that step.

I've obtained a new finishing product to test out on some samples. I've been looking for an alternative finish to the Tung Oil and Waterlox finishes, something with low or non-existent VOC's which dries in a fairly timely manner and forms a tough surface. I have found such a product from a relatively local firm, Vermont Coatings. They make a finish based on a cheese-processing by-product: whey. It looks promising and judging from the photo gallery I've seen on their site, it appears to be an attractive finish which doesn't build up any kind of a plastic-like coat. It's absolutely non-toxic. So, I'll make some tests on some Wenge and bubinga samples in various combinations, and see what happens. The company sent me free trial samples in satin, semi-gloss, and gloss to experiment with. I'm looking forward to seeing how this goes.

All for today - thanks for dropping by the Carpentry Way. Comments always welcome.

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