David's
Compact Computer Desk

We will start building the base of David's desk by sanding the leg stock to finished size and trimming the ends to finished length.  You may recall that we glued up these leg blanks from two layers of 4/4 lumber rather than cutting them from 8/4 lumber, we did that for several reasons.  One is cost, if 8/4 lumber (nominally 2" thick) were double the cost of 4/4 (nominally 1" thick) as you might think it should be then we'd break even on materials cost, but would lose money in the amount of time spent laminating the parts.  But, doubling the thickness of quality hardwood lumber often triple or quadruples the per board foot price, not just double.  Another reason is that thick lumber can hide internal defects that come to view only as you cut into the wood.  Yes, thinner lumber can do this too, but increasing the thickness increases the possibility of this exponentially.  And perhaps most importantly, making long parts out of solid wood blanks increases the chance that these parts will bow with changes in the weather.  By laminating them I can arrange the grain in such a way as to work against one another and negate the tendency to arch or bow with humidity changes.

By cutting both pieces for each leg from adjoining parts of a single board, the color and grain match up well.  By using a type III polyurethane wood glue I get a very strong hold, quickly.

Once the legs are trimmed to size and squared up nicely I use a story stick to lay out the tapers and mortises on the legs.  Orientation is important here, for all the legs are not the same, so I label each as right-front, left-front, left-rear and right-rear, and I identify each face of each leg as facing front, back, inside, outside.  With this knowledge I can be assured of getting the mortises placed on the proper faces for each leg.

Still, just to be sure, when I'm done with the lay-out I stand the legs in a group, oriented as they will be in the table, and took to see if the mortises for the various rails and stretchers face one another.  Just to be sure.

Now that I'm sure, I convert my drill press to a mortising machine by replacing certain original parts with different parts and bolting on a head that hold the hold the square hollow chisel stationary while the auger bit spins inside to remove most of the waste on each cut.  By drilling a series of square holes, I produce mortises.  If I am careful in my lay-out and machine set-up and pay attention as I work, I produce some nice mortises that require only a little cleaning up in the bottoms to be very satisfactory.

The base will be held to the case with table top fastener clips, which require a shallow groove around the top of the inside face of each upper rail, so I cut those grooves now.

Then I mount up the big miter gauge and cut another groove -- or dados actually since they run across the grain -- to form the shoulders of the tenons on each of the rails and spreaders.  Care needs to be taken that the cuts match up at all corners or we will have ugly gaps on the upper or lower edge of the rail.  This means having a miter gauge that will hold the work perfectly square to the blade, a stop block that is secure and even so when the rail is pivoted up on edge after cutting a wide face the cut resumes on the edge in the same place it did on the face.  And care must be taken to be sure the rail is held firmly against the stop block; if it walks way from the block (toward the was blade) even a little from one cut to the next, the cuts will not line up.

The tenoning jig is used next to remove waste from the cheeks of the tenon.  My jig is shop-made and rides along my rip fence.  It is not as fancy as some of the cast iron do-everything tenoning jigs on the market, but it does this job just fine.

I cut a test piece a bit wide then adjust the fence in toward the blade a hair at a time, test fitting the tenon into a mortise after each cut.  I stop when the tenon is just a bit too fat to fit into the mortise, but is close.  How much is "a bit"?  Oh, no more than 1/32", but at least 1/64".  I'll do the final fitting later.

Next I lay-out where to cut the ends of the tenons by taking the measurements directly off the mortise each piece will fit into.  I label everything as to which part it is and which end is left-right or front-back.  By matching those markings to the markings on the legs there is no question of which way a piece fits into the completed assembly.  I could just figure that the set-backs on each face are 1/4", lay them out and cut them all then worry about fitting them later, but I find that -- in the real world of hand cut joinery -- there will be small variances no matter how careful I am, so laying out these end cuts directly from the mortises is more accurate in the end.

I cut away the end waste with a back saw, using an angled cut to get the cut started so I can steer it along the line, then as the blade nears the shoulder of the tenon I tip the saw up and continue sawing down to -- but not into -- the shoulder.  I clean up any nubbins left behind with a sharp chisel.

To thin down the tenon to an exact fit in the mortise I use a narrow shoulder plane to take off a paper thin shaving from each face of the tenon then test fit.  Shave a little more if needed and fit again.  It's much easier to take a little more off than it is to put some back.

A proper fit in a mortise & tenon joint is one that slides firmly together with just hand pressure.  If you need to hammer it, it's too tight and will bind up and possibly break something once you apply glue and try to assemble the parts.  If it's loose in the mortise at all, you will not get good wood-to-wood contact and the glue will not not bond the parts together.  Glue -- with the exception of some epoxies -- has no structural strength of it's own.  Using glue to fill gaps in joinery will lead to joint failure in short order.

I fit each joint individually, then go back and put the whole thing together to be sure everything fits as it should.  The base is upside down here, but it all draws up nicely and fits square and even.  At this point I could take it all apart again, sand it, apply glue and clamp it together and have a sturdy, stable base for the top cabinet and that would be fine for a utilitarian piece of furniture, but for this snazzy little computer desk we'll need to prettify (that's mountain-speak for making something more attractive) this base some to make it a more suitable lower section for the cabinet we just completed.

We'll do that in the next episode.

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