Thread: Sliding Dovetails with the Veritas Small Plow

Interesting, Derek, & it certainly increases the range of jobs a plough can tackle. Specialty tools are great for their specific tasks, but one could easily fill the tool cabinet with one-trick ponies, so extending the range of your plough like that is very clever, I reckon.

You add a lot more taper to a sliding D/T than I do, is there some rule of thumb about the amount of taper that one should use? I aim for something less than a 1/16", more like 1/32" (on one side only), over about 450-500mm. I always put the taper on what will be the bottom side of the shelf or cabinet floor or whatever it is, & keep the top side perpendicular to the front of the piece, to make it easy to keep everything square. It only needs the merest smidgin of taper to lock the piece in place, but as anyone who has made these joints knows, the trick is to get it to tighten at the right time & go all the way home without jamming prematurely.

The amount of taper I use is just something that evolved as I went along. I started out doing SD/Ts with a router. At first I used a single guide to cut a straight trench with a D/T bit, & cut the matching part with the same bit, sizing the 'pin' so that it would barely start in its trench. Then I would simply pare off a teeny bit from the underside of the pin with a chisel (one of the places I use my long, flexible patternmakers' chisel to great advantage). That made a 'pseudo' sliding D/T, which I tried to get so that it tightened firmly over the last 25-30mm as it went home. It means the front of the D/T will not be as tight as the back after assembly, but in practice, I couldn't move or wriggle anything made that way, even without using glue. Eventually, I made a jig that allowed me to cut the trench with a taper along one edge. But I made the taper very slight, because I didn't get around to making a D/T plane until a couple of years ago, & I still had to taper the matching piece with a chisel, which is a chore on a large bookcase! Now I have my sliding D/T saw I can cut any amount of taper that I choose, and the little D/T plane I made makes it vastly easier & more accurate when tapering the matching piece, but so far, I haven't seen a need to add more taper. Am I missing something??

Cheers,

You add a lot more taper to a sliding D/T than I do, is there some rule of thumb about the amount of taper that one should use?

Hi Ian

I think that the amount of taper I use is about the same as most. Routers use either 8- or 14 degrees. What does that compare with in terms if ratios? I think it is 1:8 and 1:5, respectively. Of course there is no rule here that I know of. I stick to 1:6 because it is a good compromise, and maintaining a consistent choice means that I can gear up more easily.

I would say that I still use a saw and chisel more frequently, especially for short sliding dovetails, such as on table rails when fitting a drawer.

Regards from Perth

Derek

Originally Posted by derekcohen

Hi Ian

I think that the amount of taper I use is about the same as most. Routers use either 8- or 14 degrees. What does that compare with in terms if ratios? I think it is 1:8 and 1:5, respectively. Of course there is no rule here that I know of. I stick to 1:6 because it is a good compromise, and maintaining a consistent choice means that I can gear up more easily.

I would say that I still use a saw and chisel more frequently, especially for short sliding dovetails, such as on table rails when fitting a drawer.

Regards from Perth

Derek

I think we are talking at cross-purposes, Derek. My mistake. I thought you meant the variation in thickness of the dovetail front to back of the shelf. I took it that you vary the thickness of the 'pin' by 1/8", which is substantially more than I do when making a tapered SD for a shelf or internal cabinet component. I have seen 'how to' articles which use different amounts of taper, some quite small & some quite substantial, & I was wondering if there is some ancient 'rule' as to what's ideal. Somehow, I doubt there could be, as it serves no other purpose other than to make it easy to slide the d/t most of the way in, but have it lock firmly over the last inch or less.

However, what the pin taper ratios mean in degrees is a good question. I had to do some serious dusting of the cobwebs from my brain, & find some trig tables (Google IS handy!). So 1/6 is the tan of the included angle, which my calculator tells me is 0.166, which equates to about 9.5 degrees, rounded up. And 1/8 gives you 7 degrees, near enough.

I'm not absolutely sure of this, I will have to check, but I think my D/T router bits are all supposed to be "14 degrees". However, that must be the included angle (sides projected to a point), because they cut a profile which is so close to 1/8 that I can't tell any difference....

Cheers,