With the tails successfully cut, it’s now time to start on the other half of the dovetail joint, which is to mark out the sockets and leave the pins exposed once cut. Cutting the dovetails is relatively easy as it doesn’t really matter if there’s a slight discrepancy in the sawing, but now life becomes a little more tricky as the tails are used as a template for the other half of the joint, so the marking out has to be spot on!
The time honoured and traditional way to set about marking the pins is to place a plane on its side in front of the vice. Insert the pin board in the vice and then make the top level with the plane. The tail board is then placed horizontally across the plane and pin board ready for marking out. This method works quite well, but it’s difficult to ensure that the sides line up correctly and that everything’s square. Even when it is, during the process of marking, it’s infuriatingly easy to nudge the pieces out of position which leads to inaccuracy.
A much better way is to use a dovetail transfer jig, which will hold both pieces securely and square for marking out. A search on t’interweb will reveal all sorts of jigs but the one I like is designed by Rob Ingham.
It’s neat, compact and will enable dovetail pins to be marked out on timber which is about 200mm wide. It simply consists of a chunky block of wood with a ‘T’ section slot routed into the upper surface in which slide the two ‘T’ head bolts. There’s a pair of 50mm aluminium angle supports, one of which has some hacksaw cuts down one side to act as a ‘spring’ when pressure is applied. Full details of its construction and a working drawing can be found in Rob’s excellent book Cutting Edge Cabinetmaking.
Having used the transfer jig, the two bits of wood now need to be cramped into it. For added security, I always cramp the tail board and in this instance an Axminster Trade Clamps forged deep throat G clamp is ideal.
Positioning the pin board is the critical bit. I always used to think that dovetails fitted by correctly cutting the tail/pin interface, which is true, but a really tight fit is obtained from the shoulder line. The dovetail itself is a wedge, nothing more, which fits into a socket. If the wedge is pulled backwards into said socket, it’s bound to get tighter, so how is this achieved?
It’s simply done by overhanging the front of the tail board by a fraction (shown arrowed). When the joint is fitted together, the shoulder line slides into place pulling the dovetail tight. How much overhang is difficult to say, but a guesstimate of 0.25mm wouldn’t be far off…it’s certainly something you can feel with your finger tips. As a double check, there shouldn’t be any light showing on the shoulder line.
The pins are scribed on the end grain using a narrow V point striking knife to leave the distinctive pins marked out.
This section of the joint is then completed by transferring the scribe lines down the grain and cross-hatching the waste, ready for cutting.
Should anyone be interested in details of how to go about making Robert Ingham’s Dovetail Transfer Jig, please leave a comment below and I’ll sort something out later for a special edition Blog.