Francis Hallowes shares his secrets for creating a lapped dovetail joint with a mitred top
Step 1: set the spacing for the pins in the usual way with extra material to the top edge
Step 2: mark both faces and the bottom edge, but not the top edge
Step 3: mark the saw cut lines for the pins from their centre marks
Step 4: mark the exact length of the lap between the two furthest points of the tails
Step 5: trim the tails back on the bandsaw using a stop to preserve the waste at the end of the top pin
Step 6: the waste for the top pin needs to remain intact
Step 7: cut the pins leaving the top one in place
Step 8: mark a line for the mitre and trim with a saw
Step 9: hey presto! Exposed joinery from the side, clear face at the front and a mitre across the top edge (PHOTOGRAPHS BY GMC/DEREK JONES)
I don't know how many 'through' dovetail joints I've cut before being able to claim any degree of proficiency at this skill. This was followed by mastering a 'through mitred' dovetail. The third was a 'lapped' dovetail joint.
All pretty standard stuff so far but requires much practice to get them right. However, it seemed that there was something missing from my repertoire - a 'lapped mitred' dovetail. I'm sure this had been done before but I couldn't find any record of such a thing in my collection of woodworking manuals.
I wanted a joint like this even though a 'through mitred' dovetail makes a very attractive finish when, for example, making a box where the apex runs into a mitred detail across the top. However, there are often times when a lapped dovetail joint looks smarter for a particular design, but is let down by not having a mitre. So after many days of experimenting, I came up with a solution and would like to share the outcome with readers who, like me, never tire of learning new tricks.
As this is very much a decorative joint it's important the faces of any components that are to be seen should not be heavily scored with a marking gauge or knife. A light mark, however, can be removed with a plane afterwards.
Start with marking out the tails on the side pieces, as if they were drawer sides, with spacing for a thicker pin at the top. Mark as many tails as you like using whatever method you prefer for spacing. For this example, I started 5mm from the bottom - A - and 7mm from the top - B.
Lightly mark the outside face and mark normally around the bottom and normally on the inside face. Do not mark the top edge. Usually when marking for a lapped dovetail the tails are about 3mm shorter than the thickness of the timber to allow for the 'lap', but in this case mark to the full thickness - you will see why in due course!
Mark your cut lines for the tails with zero thickness at the thin end. These will increase in size later when the tails are shortened.
Now mark the end of the front piece for the 'lap'. If the timber is between 10 and 16mm thick then make it a 3mm lap. Do not extend the line to the full width of the component. Stop 6mm short of the top and bottom edges - C and D.
STEPS 5 & 6
Now back to the tail piece. Mark 3mm - or the same thickness as the 'lap' - in from the ends of the tails and trim them back to the line, starting at the bottom. Do not cut off the top small tail. I make this cut on a bandsaw, using a sliding mitre attachment set at 90° with a stop on the fence to avoid any possibility of cutting off the top tail.
You can now mark out for the pins and remove the waste in-between, except for the top pin. This will be mitred from the outer face corner and not cut square.
STEPS 8 & 9
To do this use a mitre gauge or sliding bevel to mark from the baseline scribed on the inside of the box - E - to the external corner on both pieces - F. Cut a little proud of the mark and trim with a chisel to establish a good fit.