Patching a Poorly Cut Dovetail

I've been practicing by making boxes with half-blind dovetails and frame and panel bottoms. Although I was taught to cut near the line and approach slowly and carefully, I know it is faster to cut perfectly with the saw. So I've been cutting right to the line and dealing with the consequences, knowing I will spend more time now for reduced time in the future.

The first two joints came out quite nicely, but on the third joint my hope for the best didn't work so well. I wrote last week about cutting on the wrong side of the waste line. The good news is that my practice of cutting to the line meant I was only one saw's width too wide instead of more. But there was a saw's width gap.


I didn't think that could be fixed with a simple wedge (as I plan with the bottom side of the same tail), so I decided to patch it with some of the waste generated while cutting the pins.

The first step was to identify a waste piece that would fit, and make sure it fit snugly. I chose to patch the pin rather than the tail, because end grain is less likely to show noticeably. Then I made sure the side and corner of the tail were square and flat.

Even though my chosen waste piece had a flat section, there was a notch where I had started the chop. I needed a safe way to flatten this, and a chisel was definitely not that way. While puzzling over this, I remembered a miniature plane that might work. It looked to be just right for this application, so I tuned gave the blade a quick flattening and sharpening. Then I clamped it in the vice and ran the intended patch over it until it was flat.

Note: Looking at the picture, I realize this probably is not safe for the ends of my fingers. I was lucky and did not make finger shavings. Let me know if you have a safer idea for how to do this in the future.

Then I used a chisel to cut a matching angle for the bottom edge and test fit the patch to the tail.

Glue up was next. I used Tightbond II and a small c-clamp to attach it.
After letting that sit for a day, I trimmed the patch flush with the pin.

Then marked it for a new cut.

And trimmed to the line with a chisel. Actually, I trimmed past the line on one end (insert a favorite string of curses here) but the result is much better than I started with. The remaining gap can be wedged during glue up or hidden by peening the end grain.

Dovetailed Box #4: Dulled Chisel and Mis-cuts

Last night I retreated to the shop to work on box #4. I hope to complete this and two others before the end of June. The first two joints went incredibly well, but joint number three has become an opportunity to learn.

Lately I've been cutting tails first, and this box is no exception. I checked the tails for square and fixed any that were off. Then I marked the pins using an Xacto knife (a recent Fine Woodworking review rated this as the best value in marking knives. The reviewer was right: an Xacto works brilliantly, especially compared to the mechanical pencil I had been using).

At this point I felt good. The pin layout looked great, with crisp lines. The waste areas were marked to prevent my making more tails where I needed pins. I had even caught an error made during initial layout, where I had marked the wrong side match up on the end piece. This could have been a disaster, resulting in an Escher box with two bottoms.

In fact, the first cut looked great: I had matched it exactly to the knife line and followed the inside edge of the marked pin exactly. A moment's satisfaction and I was ready to make the second cut. That's when I realized: I had cut on the wrong side of the knife line. I didn't cut waste. The joint was guaranteed to have a saw-width gap there, just waiting for repair.

I could have quit then, but I hate to stop work when I've just made a mistake. It leaves me sour, and depressed. So I calmed myself and planned out how to patch this with one of the waste pieces. Then I settled in to complete the pins. The rest of the night brought some challenges, but nothing as painful as that initial miscut. I finally had to stop when I realized the chisel was dull. I'm not sure how I managed it, but I must have knocked the cutting edge into the holdfast. There is visible flat spot on one side, but the rest of the edge looks good. Tonight I expect to be sharpening for a while to get that out. Now I wish I already had a grinder...

Dovetail Error #2

No, this is not a mock up for next year's jack-o-lantern teeth, but a real life example of cutting the tail instead of the waste. This demonstrates why you should always mark the waste, on both visible edges, before starting to cut and chop.

It almost makes me feel better that this error is over a year old. And it was a mock-up using scrap wood. And I was hurrying.

My New Year's resolution? Work smarter, not faster. The speed will come, and going slowly once is still faster than going quickly twice.

Dovetail Error #1

Notice the chisel (my thinnest) and how it compares the the waste area next to it. If your thinnest chisel is a 1/4", you cannot cut pins that run to the width of the saw kerf: your chisel will be too wide to remove the waste.

Dovetail Errors of the Past

In my basement shop I have my first "successful" project in wood. I put that in quotes because the criteria for success were pretty loose: could I make dovetails that actually seemed to stay together by themselves? I did pretty well for such a complex first project, but you can see the single nail in one of the pins that says "not quite"

There were a number of mistakes that preceded the making of the dovetails, (like trying to smooth wood scavenged from a pallet without first checking for nails, not making the boards flat and square, and not actually knowing how to sharpen a plane blade OR a chisel very well, but that's all for another day). But I was making dovetails, and I was not daunted by a lack of knowledge. I had read instructions for making dovetails several times before, so I thought I had the right idea: mark out the pins and cut them, mark the tails from the pins and cut them, put together the box and wonder how you ever became so clever. So I did just that and was very satisfied.

Of course there were a number of execution errors (obvious in these pictures), but there was a major layout error too. One I've seen other woodworkers duplicate (including one whose project was featured in a major woodworking magazine): I'd created half tails instead of half pins. I think anyone layout out dovetails for the first time is likely to do this if they don't have guidance: It just seems logical to put those satisfying visible angles in as many places as possible. But the experts all tell you to use half tails on the ends of a join, and after much puzzling about the joint structure and wood movement, I think I know several reasons why.

1. If the wood cups,half tails allow it to happen much more easily
2. There is less distribution of pressure across the grain structure, making it more likely for joint failure at the corners
3. If you are making a half blind joint to allow a panel bottom, you need to place the panel groove much higher in the frame, losing some of your drawer space to the underside.

There may be other reasons, but these are the three I've encountered so far. Next time you look at a well made dovetail, take a look at those half tails and try to picture the forces on them. You'll begin to see how having these cap the joint makes it much more difficult for cupping to occur in either panel that if it had the straight on angle of a half tail.