With a router and a dovetail jig you can cut perfectly-fitting dovetail joints easily – just so long as the dovetail jig is set up properly in the first place.
What this means is that setting up to rout machine-cut dovetails is always a trial and error process. There will always be lots of test cuts on test pieces and adjusting of the jig to get a perfect fit.
The main problems that you can encounter will be joints that are either too loose, too tight, too shallow or too deep or that the work pieces are offset (or if you’re really unlucky, a combination of the above). Luckily each problem is easily rectified by a simple adjustment, but you do need to make notes for the future so that you don’t have to go through the whole process again next time.
If the joint is too loose so that the joint moves around when it’s put together, the depth of cut is too shallow. Increase the depth of cut and try again.
If the joint is so tight that the pieces can’t be tapped together, the depth of cut is too deep. Decrease the depth of cut and try again.
If the pins on the drawer sides go too far into the sockets on the drawer front, the sockets are too deep. To correct this, move the template towards the front of the body of the jig – make sure you adjust both ends of the jig so that the template is square .
If the pins don’t go far enough into the sockets, move the template towards the back of the body of the jig.
Top of the range jigs, such as the Leigh D4R, have built-in scales at each end of the template to provide rapid and accurate fine adjustment for different stock thickness and through-dovetail fit, helping to keep the template perfectly square.
If the top edges of the two pieces aren’t flush when you assemble the joint, the problem is probably that the pieces weren’t tight against the stops, or that the stops weren’t properly aligned.
Jigs such as the Leigh D4R have the stops machined into the body of the jig so that this can’t happen – you just have to make sure that the work is tight against them.
And Don’t Forget
Once the initial setup is taking care of, then you can easily make beautiful, accurate dovetails – and don’t forget to make a note of the settings for the future so that you don’t have to do it all over again!