Rounded dovetails

Dovetails are visually stunning and of course they are structurally strong. What's more stunning then dovetails?Rounded dovetails!
The first time I seen a rounded dovetails, I was amazed at how good they looked. So I looked into them in more depth, and I found that there was a lot of people petrified of them. Statements like 'your dovetails have to be perfect' can and do put people off.
If your thinking of rounding your dovetails, chances are your dovetails are pretty good anyway. And even if there not . Just a few simple steps will give you good results.
Below are the steps that I follow, that give me good results cutting dovetails so I can round them, if I choose to.
I always start with my ends square. Not close , square. I then pencil the thickness of my material on one board. I don't allow extra when doing this,
I shoot for getting it to the thickness. When you chisel out the Waste later, you WILL move your knife wall back. So allowing extra, is just more to plane down later and more work and time.
With the thickness marked, I set a cutting gauge to that line, and create a knife wall on both faces (this can be done with a square and a marking knife). On what will become the outside face, I lightly mark,  so i can plane that mark out , without to much work On the end of the board I mark out with dividers. When I'm happy I pencil in the divider marks. I use a dovetail template to mark out the tails. I only pencil in the right line of the tail on each face. I find it a little awkward to see, and cut the left side.
So I cut all the right sides, turn the board around and repeat, I find this quicker, easier.
That's all the tails cut. I then remove the two end pieces, cutting slightly away from my knife wall. I finish up with a chisel.
On the inside face I create a valley all the way along the knife wall with a chisel. I deepen the knife wall with a marking knife and repeat.
I then take a few passes with a router plane. This gives me a shallow rebate. You only need to 1-2mm , there's no need to go any deeper like 6-10mm like I have seen , again , it's just more work.
On the outside face, I use a marking knife to deepen the knife wall. I only deepen the waste sections that are to be removed. I use a chisel and create a valley on those sections. I'll repeat this once more to deepen the valley. This will minimize the chisel moving the knife wall back.
I then remove the waste section's in between the tails. I do this with a coping saw. I aim to cut about 1mm above the knife wall. This way the chiseling is easy , and your less likely to take out big chunks of end grain.
I lie the board on the bench and chisel out the remaining waste, chiseling out just over half way on each waste section. Flip the board and repeat. I then put the board back in the vise. I can then see if there are any high spots, I chisel these flush if needed.
I'm then ready to mark out the pins. At this point , I check I don't have any cupping, especially if my boards are wide. If i do , a straight piece of scrap wood across the width, with a couple of g clamps , will pull the board straight.
I place the pin board in the vise, and level it with the height of a plane. I place the tail board on top of the pin board. I use the plane to rest the back end of the board.
I then line the boards up. This is where the small rebate I made earlier , comes into play. It lines things up quickly and accurately. It all so stops any twisting in the joint , due to misalignment.
I pencil in the pins with a sharp pencil. I use a square and pencil in the face lines, create a knife wall with the same set gauge from the tails. I then cut the pins. When I cut the pins, I cut the left and right sides , on the same face, unlike the tails. Sometimes the back of the saw cut can wonder.
when cutting the pins , I cut to the waste side of the line, and leave the pencil line on. This will ensure your joints are not slack. I then remove the waste in the same manner as I do with the tails.
I am now ready to fit the joint. On the inside of the tail board, I remove the corners of the tails but, not all the way to the top. This will aid the entry of the pins.
I Line everything up , and try to tap the joint together. If the joint is to tight, I clean the pins up very lightly, and I do mean lightly. Basically cleaning the saw marks off. Check the joint for fit. I try to identify if there is any portion of the joint that is fitting , especially if the board is wide. The tight sections I mark, then clean the saw marks of the tails I've marked. At this point I nearly always still have some fitting. So I check the joint as before and mark what is to tight. I under cut the pins where needed very minimal. I leave about 2mm at the outside edge and about, 3mm down from the top. I then take a thin shaving with a chisel. Leaving the top and the outside, will reduce the chances of gaps. And those thin 2mm and 3mm section will compress.
I use my marking knife and remove the shavings. If the joint is still tight (which it's normally not) I repeat under cutting on the tails. Taking your time through this process will give you good results, don't rush it.
After you have glued up your joint and let it dry, flush the joint square with your plane. you can now start rounding or leave it as is.  If you've took your time with the fitting, you should have a nice fitting joint. So there should be no issues or doubt about rounding it.
The rounding over is easy and quick. I mark out usually with a 2 pence piece.
Where the ends of the curve meet the outside of the boards, I pencil this mark across the width of the board, with my fingers. I clamp a piece of scrap to the end of the board , to stop break out. I start planing on the peak of the corner. I aim for about 45° , and stop just shy of the top of the 2 pence pencil mark
. I now have two peaks, so I repeat several times. I will often swap to a smaller plane , which is set lightly, when I have most of the waste removed. I pretty much have the round. I finish off with some 120g sandpaper and I'm done.
I've been using this process for a while and , I always get good results. I think the key is not to rush , and not to skip any steps.
The end result is a eye catching joint, that is strong and will last a lifetime.

Here is a rough and ready high speed video, of me cutting some dovetails.


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