Even the best woodworker sometimes get gaps around their dovetails or box joints, This is probably more of a problem for hand cut joints than ones done with a router jig. It can be pretty frustrating to get just one or very few gaps when the rest are all ok. The problem is that someone who wants to show off their craftsmanship certainly does not want to fill gaps with wood putty or other fillers because it’s pretty obvious.
A couple of years ago I read in FWW magazine about how to fix the gaps without fillers. Since then I have used this technique when necessary and it works very well. It isn’t good for huge gaps, so don’t expect more than the technique can deliver. Really big gaps should be fixed by inserting matching wood into the end-grain. Normally you should not try to fix side-grain.
I cut some dovetails on my scroll saw to demonstrate this technique. I deliberately cut the tails too wide in order to get a gap. I like to cut the pins first because it’s easier to clamp the pins to the tail piece for tracing the pattern and it’s also a lot easier to get in with a pencil or knife to trace with. Also, when you trace the pins onto the tail piece you will know that you have to save the lines on your tail piece for a tight fit. I like to cut dovetails on my scroll saw because I don’t have to do any chisel work at all. I do have to use a coping saw to finish off a small amount of waste on the pins, but this is very easy and quick. I can cut dovetails by hand, and sometimes I do just to keep my hand skills current, but the scroll saw is my favorite way, and they still look hand-cut.
The first two photos shows the finished joints with the gaps.
In the first photo below I have spread extra glue around the gaps after having glued up the joint. The glue has been rubbed in the gaps in the second photo.
Now the fun begins. Start tapping the end of the pin. More taps and less force is the way to go! Start from the center of the pin and work outwards towards the side where the gaps are. The ball on the hammer spreads the wood into the gap. If your dovetails are too small for your pins then a steel rod of appropriate diameter ground to a round shape on the end can be used instead. It is important that you make the shoulders wider by a little more than 1/32” to give you some extra pin and tail ends (end-grain) to pound on.
Here is what it looks like before chiseling, planing or sanding the pins flush with the tail surface.
Here is the result. I didn’t hammer the ends of the tail pieces, but I’m showing it to remind you that I could have.
You can see that the dovetails are not very consistent in size. I didn’t take the time to mark them up as good as I could have as I was supposed to be in the shop to clean it up so it would be ready tomorrow when my grandson comes to work on his box. I apologize for the fuzzy pictures. My camera doesn’t have a macro function, so closeups don’t come out to well. I hope you try this out. It really works well. Thanks for reading.
-- Mike, an American living in Norway.