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It occurred to me while building the seventh drawer for the chest that I have demonstrated the making of half-blind dovetails on a couple of occasions, but never through dovetails.
Each dovetail has its own particular challenges, and in some ways the through dovetail is the more difficult to hide inaccurate sawing.
Here, the through dovetail is used at the rear of the drawer. It does not have the show quality of the front of the drawer, which uses half-blind “London” (skinny) dovetails. It does not have to be as strongly built either, since it is not load bearing as the front dovetails are. Fewer dovetails may be used. Care is still a priority, as sloppy dovetails will show through at the corners when looking into the drawer.
The Tail Board
The tail are cut first. Three tails have been chosen, with an angle ratio of 1:7 to match the front dovetails. The apex is 3mm wide.
Typically, I choose to mark and saw from the show side. In a box, this would be the outside face. For half blind dovetails it would also be the outside. However for through dovetails for a drawer it is the inside face.
Blue tape is placed along the base line both front and rear to ensure that the saw cut does not extend over the baseline. Over cutting would show on the inside of the drawers.
Once the tails are sawn, deepen the baselines and undercut them to create a chisel wall.
The waste is removed with a fretsaw (more on this shortly), and the remainder is pared with a chisel (more on this shortly as well).
With the tails completed, they are transferred to the pin board (below) ..
The Pin Board
Use has been made of blue tape to ensure crisp marking (the advantage of this method is not only are the lines very easy to see, but only a single knife stroke is required to make the mark, that is, to slice through the tape. When multiple strokes are required to ensure a deep and visible mark, this line is inevitably thickened). See Half Blind Dovetails With Blue Tape for additional information.
The first saw cut is made full length, but just enough to score the surface. Kiss the line – saw as closely as possible.
Note that the saw is held very lightly, and pushed with the heel of the hand. If you are experiencing difficulty starting a saw cut, it is most likely that you are holding the saw too tightly. Loosen up.
Once the horizontal line is sawn, drop the saw and begin cutting at a diagonal, following the vertical line.
Just before you reach the bottom of this cut, level the saw and finish the cut on the horizontal.
When making the saw cuts, the saw must be stable … not waggling around.
Use a thumb to support the saw.
Finish all the saw cuts tight to the line (above).
The blue tape is now discarded.
As before, the next step is to deepen the lines between the pins. I am using a wheel gauge here.
Once the lines are deepened, use a chisel to undercut them and create a chisel wall.
Next I saw off the ends. Once again, as close to the line as possible. At best, there is no waste to pare away. At worst, this takes a couple of strokes.
The waste is now removed with a fretsaw. I aim to saw along the top of the chisel wall. This should leave about 1-2mm of waste above the line.
As with the saw, the fretsaw must be held as lightly as possible. Never force the cut. Let the saw do the work. A way of determining how you are doing is to watch the blade – it should hardly deflect. You should be rewarded with a fairly straight saw cut.
The pin board with waste removed.
I try and take shavings of about 1mm. The final cut is taken with the chisel against the chisel wall (where it cannot be pushed back over the baseline).
The aim is to only pare half way through the board. Once one side is done, flip the board and do the same again.
A comment about the technique I use: The first chisel cut is vertical and halfway through the board. This is taken from the show side (the square is for demonstration – one is not otherwise used).
The second chisel cut, on the flip side, is at a slight angle ..
The reason for angling the chisel slightly away from the board (opposite of undercutting) is to avoid damaging the show baseline due to striking through.
The result is a slight triangle at the middle of the board. This is pared away …
Use your fingers as a depth stop to prevent paring deeper than the triangle of waste.
I prefer to tap the rear of the handle with the heel of my hand, as opposed to pushing the chisel, as this affords greater control of the cut. It is too easy to over-push the chisel (and damage the show side).
I prefer a narrow chisel (typically ¼”) to remove the waste. A slight undercut at this point is fine – this section of the joint is not structural, that is, it does not hold glue well (as it is end grain to end grain).
Bringing it together
Once done, chamfer the inside edges of the tails. This is to prevent any damage to the corners of the pins when the two boards come together.
So here are the tail- and pin boards. Will they go together off the saw? Or will they require some tuning? The Big Moment!
A few light taps and the two go together very nicely. (As if we had any doubts .. ).
One of the reasons for clean, tight fittings is this … this inside of the drawer shows no signs of being dovetailed.
Here is a view of the glued up drawer carcase (yet to receive the slips and drawer bottom).
After gluing, I pop the drawer into the carcase, and let it dry there. This ensures that any irregularities in the drawer are matched to the inside of the carcase.
Regards from Perth