IPG 6/15/19 meeting summary – Demilune Table Project
The meeting with Owain Harris began at 1:00 PM in his shop at the Gonic Mill Building in Rochester, NH. It was another busy day with Owain sharing several interesting tips and techniques from his archives of knowledge and experience. Today’s primary focus was on the mortise cuts into the curved apron that will be used in this project.
At the end of the last meeting the bridal joint tenons were cut into the top of each leg using the bandsaw. A ¼” spiral up cut router bit was used to make shallow 1/8” rabbit cuts along each edge of the front tenon cheek. One final step, each leg post top was adjusted (reduced) from 1 ¾” square to ~1 5/8” - ~1 9/16” before today’s session.
- The excess material at each end of the curved apron needs to be removed and squared for joining with the straight back apron piece. After doing the layout for these cuts with the MDF template, each end of the curved apron is trimmed off at the table saw using a fixture Owain has fabricated similar to an L-fence that is clamped to the rip fence using a MicroJig Matchfit Dovetail Clamp. Owain uses double-faced tape to hold a straight edged strip of wood to the top edge of the apron, placed precisely at the layout lines. This straight edge will ride along the straight edge of the L-fence that extends out above the saw blade. Because the table saw blade would not cut through the full width of the apron in one pass, it is critically important that the saw blade is checked to be square to the table before making the cuts. The first pass cuts approximately 2/3 through the width of the apron. Owain repairs a slight tear out chip in the corner of veneer using CA glue. The apron is now flipped over and similarly set up to make the second pass cuts at the table saw.
- At the bench the next step is to do the layout for the two 7/8” slip tenons that will be used to join the curved front apron to the straight back apron. Owain notes that he makes his own slip tenons at the table saw, doing final shaping as needed with hand tools. He says beech and hard maple are two good wood choices for making slip tenons. Now the apron is held in the front vise with one end positioned up at a good height to make the cuts for the twin mortises for the slip tenons into one end.
- A platform jig was made with edges that are parallel to the twin mortise layout lines and an attached fence underneath to clamp the platform in position to the apron. A plunge router is used with a double fence setup. Each fence will ride along the parallel edges of the platform and a spiral up cut router bit positioned in perfect alignment with the twin mortise layout lines. Layout of the mortises reference in approximately 1/8” from the inside face of the apron. The depth of each cut is set at 7/8” x ¼” thick x 1” wide. Slip tenons are cut to 1” (using the width of the 12” Starrett rule) x ¼” thick. First cuts are done to a properly dimensioned piece of poplar to test the fit.
- The rear rail is ¾” thick with a 1/16” offset from each edge. Divide the apron edge into thirds (¼” x ¼” x ¼”) and layout the ¼” thick mortises in the middle ¼”.
- At the bench the curved apron piece is placed on MDF template that shows the location and details of each leg joint. Layout of the mortises for this joinery is marked using the MDF template. Owain demonstrates how to make a router jig out of a square piece of ½” MDF, with a slice of the middle section cut at the table saw to precisely match the width of the bridal joint leg mortise. The middle piece is then cut in half so that the original piece of MDF is now four pieces with the two middle pieces positioned between the two wider outside pieces. Before gluing these pieces back together, the two middle pieces are spread apart to slightly more than the width of the curved apron, leaving a perfectly sized opening to make the leg mortise cuts, between the rabbit cuts of each front tenon cheek, using a flush cut bit with a bearing. The excess pieces extending out of the middle section of the jig can be cut off after to glue has set up. The jig is now ready to use for the leg mortise cuts.
- The apron is locked in the front vise at the bench and the mortises are cut using a trim router with a 1/2” flush cut bit with bearing guided by the MDF Template. After the outside mortises are cut to fit the tenon between the rabbit cuts the jig can be positioned to cut up to each layout line of the rear mortises. Remember that the rear tenon cheeks do not have the additional shallow rabbit cuts. For all these wide bridal joint leg mortise cuts Owain recommends clearing out the edges of each cut first, and then go back to remove the waste from the middle of the mortise.
- Owain notes that each leg mortise routed into the apron is cut to fit a specific leg. In other words, the legs are not interchangeable. In theory, each leg is the same size. Nonetheless, fit one leg specifically to one mortise, make note of it, then set it aside and repeat the exercise for each leg.
Owain’s quote of the day “ You don’t really make less mistakes the more you do something, you just get better at fixing them!”
The next meeting is on Saturday, 7/06/2019 at 1:00 PM. We will be shaping the legs using a drawing template made of ¼” Baltic birch (or MDF). A drafting spline will also be used to determine the desired curve of a part (available on Amazon).
Epo-Tech Epoxy – a good 2-part epoxy with a 2-yr shelf life. $250 minimum purchase required, which is enough for five kits.
Robert Wyatt, 07/05/2019.