Magnetic Dovetail Guide
I cut all my dovetails by hand, but like David Barron and others, I like to use a magnetic saw guide to keep all the angles consistent on both the pins and tails.
There are lots of guides on the market.
I figured I could build a similar one for not a lot of money, so I did.
I came up with this design and have used it for about 3 years now and it works really well.
This guide can be made for any angle you like. 1:4 - 1:6 - 1:7: - 1:8 - or even 90 degrees if you just want a jig to help you make perfectly plum cuts with a hand saw. Make several different ones if you want.
I'll be using hand tools for this build, but if power tools are your thing, have at it. Just be aware that this piece is not very big and has some funky angles.
This is what the final piece looks like so you have an idea of what we are shooting for as we build it.
We are going to need six (6) neodymium magnets and some 5 minute epoxy.
These magnets are 12mm x 3mm thick and they will fit very nicely into a half inch hole with enough room to spare for the epoxy.
You will also need a wood block cut to 2 1/2" x 2 1/2" x 3/4" thick. make sure all six sides of this block are square and parallel.
The species doesn't really matter, but I do recommend that it be a hardwood. This one is Walnut, Maple would be great too.
The first thing we need to do is set a marking guage to the thickness of our piece.
Mark a line from one of the end grain sides all the way around.
Cut it off at the line.
Now that it is cut we ar going to rotate the cut-off to the bottom of the larger piece.
A little more...
The reason to rotate it around is so that the two freshly sawn edges are next to each other at the top.
The previously squared up end grain is now in this position and creates a shelf that has to be exactly 90 degrees to the inside face.
It also needs to be 90 degrees to the edge, and by rotating the cut-off we accomplish this in just one move.
Now we glue it in place.
Don't use too much and keep it away from the inside edge.
Squeeze out here on the top is no big deal.
Squeeze out in here can be a headache.
Put on some clamps and double check for square.
Triple check for square, it's critical that this particular edge is square.
While the glue dries we can set up to cut the angle on the guide.
This guide will be 1:7.
Set an adjustable square to 7" and put it against the edge of your bench or some other scrap board.
Mark a line all the way down one edge of the scale and also a short line on the other edge of the scale. In a 12" adjustable square the scale is almost always 1" wide, double check yours to be sure.
Connect the ends of the lines and draw a new line.
This is a one in seven pitch (1:7)
Draw an eight inch line for 1:8, or four inch line for 1:4.
Use a bevel guage to capture the angle.
Now that the glue is dry I take it to the shooting board or put it in the vise to finally clean up the sawn edge and get rid of any dried glue squeeze out.
We are going to take our angle and mark it down the long grain face of our block.
And mark a square line down the end grain edge of the block.
Do this on both sides and make sure the angle runs in toward the middle of the block. Like this.
The easiest way I found to hold this piece for sawing was to just clamp it right onto the fence of my bench hook.
I'm going to saw the righthand side first. I'll start at the far edge and slowly lower my saw and follow the line. Once I have a kerf established I will lower my saw and concentrate on cutting down the face keeping my cut plum.
I use a dovetail saw for this cut.
I flip the piece to the near side of the fence and cut the other side of the guide.
I work across the top and down the face to stay right on my lines.
There you go, beautiful right? Were done right?
No; we've got more to do.
Let's clean up the saw cuts using a block plane and maybe a smoothing plane.
Use the bevel guage to make sure the angle is the exact same on both sides of the guide.
Make sure that where the angle starts on the end grain side is perfectly sqaure too. This is just as important as the angle.
The angle has to be right and it has to be square to the face all the way down.
Check again just to be sure.
We haven't even touched this one, but what the heck, check it too.
Let's add the magic of magnatism...
This is one of sides with the angle; mark a line down the center of each leg and use that same setting to mark crosshairs up from the bottom of each leg.
Since it's an angle i use the bubble level in my adjustable square to make it sit flat in the vise.
Mark the centers of the crosshairs and use a 1/2" drill bit or forstner bit to cut the recess for the magnets. Three on each side.
You want the magnet to sit about 1/16" below the surface. it will be completely covered by epoxy later.
I just used some CA glue in my original jig and it failed after I dropped it a couple times. I think having the mags completely covered in epoxy will prevent this.
Set things up and mix some 5 minute epoxy. Enough for all three mags on this side.
Begin by just wetting the first hole, don't fill it up.
Put in the magnet and press it down to the bottom and then apply more epoxy to fill the hole.
Be very careful when applying the second and third magnets, they are stronger than you think and now I've got a mess.
It jumped out of the hole and connected to the first magnet and I had to use a ruler to get them out and now there is epoxy everywhere and it's a mess.
Don't panic, it happens. Make sure you have a rag or paper towels handy and some denatured alcohol too.
Let's start again.
Put the first magnet in and press it down.
Fill the hole and cover the magnet with more epoxy.
Do the same for the second and third magnets and make sure they are all covered with enough epoxy that it stands a little proud of the surface and give them time to dry. A lot more than just 5 minutes too.
After a couple of hours flip the piece and repeat for the other side. Except skip the part where the magnets went crazy and made a big mess. We've already learned from that mistake.
I usually give it till the next day before I clean things up.
Use a chisel and a block plane to bring the epoxy down flush with the surface of the wood.
Rub on some 150 and 220 sandpaper glued to a flat surface, glass in my case, to make it really smooth.
We're basically done. use a sanding block to soften all of the edges and corners.
Use some chisels to mark the angle if you want.
OK we made a block and cut some angles in it... How do we use the darn thing?
First off it can be used to mark out your dovetails with a pencil or making knife.
Use both sides of the jig for both sides of the dovetail.
Secondly and most importantly you clamp it in place and let the magnets hold your saw at just the right angle so that all your dovetail cuts are exactly the same.
The magnets alone are holding the saw in place and it's leaning.
I'm not cheating, the saw teeth are not even engaged with the wood.
But when they do engage, look out. The cut across the grain is perfectly 90 degrees and the angle is the same all the time which is key to great dovetails.
If you're a righty and have trouble cutting on the other side of the jig, or vise versa, just flip the board and the jig in the vise and keep on cutting the way you're most comfortable.
Now for the pins...
The guide is used just as before, but this time we run the angle across the end grain of the board instead of down the face.
It clamps in place just like before.
The magnets still keep the angle right and the cut perfectly plum.
Perfect angle, perfectly plum.
All that's left to do is apply a coat or two of your favorite shop tool finish.
Oh yea, I almost forgot to show you that this guide works with both western and japanese saws.
Sorry about the wet look, but I had just applied some finish to the guide.
I really like how small the kerf is with a dozuki saw.
Some people have asked me in the past about wear from the set of the teeth and it's true, over time you will get some wear. The great thing about having the magnets set below the surface is you can take the guide to some sandpaper and have a fresh clean face in no time.
I hope you found it usefull.
I'd love to hear comments, questions, or critcisms (as long as they are constructive).
Thanks for following along.