Half Blind Dovetails

[James Jayko]

So I've taken to hand cutting dovetails (and by hand cutting, I mean with a guide). My through dovetails come out basically perfect at this point. But whenever I try to do half blinds, I always end up creating a not all that great gap at the front edge (where you leave the ~1/8" that is visible from the front. I know this is just one of those things that I'll get better at with time, but does anyone have any pointers for how to cut half blinds? My process, at this point, is:

1. Saw the best I can
2. Chisel back close to the marking knife line.
3. Take a final pass with the chisel on my knife line.

I assume that at a minimum, I am trying to take too big of a cut on that last pass, compressing the fibers in the front of the drawer face. But any other pointers for how to improve my half blinds? I realize that I don't even really know what I'm asking, so any tips or pointers would be greatly appreciated!

[Derek Cohen]

James, there are two immediate thoughts I have about the cause:

1. The back of the socket is not perpendicular - is instead slightly ramped - or there is waste that needs to be removed to enable the tail board to fully enter the pin sockets.

2. You may have pushed the baselines of the tail board back a smidgeon when removing the waste. I always create a chisel wall before removing the waste.

Check these first.

Regards from Perth

Derek

[Jim Koepke]

What Derek said and a bit more.

With half blinds the saw can't make a kerf all the way in to the corner at the base of the socket. It helps to have a kerf maker tool:

Using the Bontz Kerf Maker.jpg

This is a commercially made tool. Before getting this a piece of broken saw blade was used. The edge should NOT be sharpened but instead it should be flat. (a sharp edge is more likely to split the wood) The kerf tools should be the same thickness as the dovetail being used. If my memory is working Frank Klaus used a piece of bandsaw blade with the teeth filed off for doing this.

For me it always seems to work best if an extra kerf is cut in the middle of the socket. This makes waste removal much easier.

Before cutting down on the waste (with the grain) my chisel is lightly driven in just above the baseline. Then the downward cut of the chisel pops the thin piece of waste right out. With the kerf in the center of the waste there is no tendency for the sides of the socket to block the waste from falling out.

3. Take a final pass with the chisel on my knife line.

This was one of the reasons for my dovetails to always seem a touch sloppy. The knife line is made when transferring the layout from the tails to the pins (or pins to tails) by running a knife (or pencil) along the edges of the previously cut half of the joint. The knife line is not in the waste.

Another helper for me to up my game was to use a straight edge clamped to my tail board when marking pins:

Pin Marking Set Up.jpg

Others use the rabbet trick (aka the #140 trick) to help register the tail board against the pin board for marking. This involves using a rabbet plane to create an edge at the baseline of the tail board.

jtk

[James Jayko]

When I said 'knife line,' I meant the line I created with the marking gauge. Same problem? I assumed that was spot on; its always worked to take that final pass right on the gauge line for through dovetails...

[Ben Ellenberger]

Derek called out the two most likely causes. For me, the gaps in my first few were due to the back of the sockets not being vertical. It is really easy to do.

It sounds like you are sneaking up on your marking lines when you remove waste from the sockets. This is a good approach. When you think you have the back wall vertical, try to pare a tiny undercut to make sure it isn’t holding you off. You can also trim the inside edges and corners of the tails to make sure they aren’t holding you off. They will be hidden inside the joint.

i wouldn’t make it a habit of undercutting the socket walls or trimming too much off the tails, but doing a little on one or two practice joints will give you a good feel for the kinds of things that keep the joint from closing up.

[Jim Koepke]

When I said 'knife line,' I meant the line I created with the marking gauge. Same problem? I assumed that was spot on; its always worked to take that final pass right on the gauge line for through dovetails...

The words that finally helped me, "cut to the line, not through the line."

Without an infinitely thin blade on the marking gauge it will likely be slightly beyond the edge of to what it was set. A wheel gauge will likely have a slight bevel. A pin gauge will have the angle of the tip. A flat edge on one side of a knife ground pin will still have some thickness to make the line wider.

The final step in learning to cut dovetails is the relationship between the line and where saw and chisel cuts are made.

jtk

[mike stenson]

Well put Jim. I want to still be able to see the polished edge the knife line when I'm done cutting. I also check all surfaces for square before I start to put anything together. These are the two things that always plagued me. If I rush it, they still do.

[Warren Mickley]

There is another flaw that could cause the gap at the front. That is that the sockets on the tail board are not as deep as the sockets on the pin board. These two lines ought to be marked with the same marking gauge, with the back of the drawer front being the reference surface.

[Jim Koepke]

There is another flaw that could cause the gap at the front. That is that the sockets on the tail board are not as deep as the sockets on the pin board. These two lines ought to be marked with the same marking gauge, with the back of the drawer front being the reference surface.

Yes! It is amazing how easy it can be to forget to check the obvious.

jtk

[Andrew Pitonyak]

What Derek said and a bit more.

With half blinds the saw can't make a kerf all the way in to the corner at the base of the socket. It helps to have a kerf maker tool:

Using the Bontz Kerf Maker.jpg

This is a commercially made tool. Before getting this a piece of broken saw blade was used. The edge should NOT be sharpened but instead it should be flat. (a sharp edge is more likely to split the wood) The kerf tools should be the same thickness as the dovetail being used. If my memory is working Frank Klaus used a piece of bandsaw blade with the teeth filed off for doing this.

I own a Kerf Maker from Ron Bonz as well. Some people make their own. This really helps me.

[steven c newman]

Mine was made by Red Devil....steel blade, rosewood handle, brass rivets.....welcome to try it out, sometime..

[Tony Wilkins]

Is anybody making these kerf maker tools currently? Looks like Ron is pausing orders to catch up on his backlog?

[Jim Koepke]

Is anybody making these kerf maker tools currently? Looks like Ron is pausing orders to catch up on his backlog?

Any chance you have access to any scrap metal? It isn't hard to make something that will perform the task.

If not maybe you can find out what the Red Devil tool Steven uses is called and look it up in the local hardware store.

My first kerf maker was a piece of saw blade.

jtk

[James Pallas]

Is anybody making these kerf maker tools currently? Looks like Ron is pausing orders to catch up on his backlog?

Of course most things written here are opinions. This is mine. Number one, you don’t need it is just one more tool and one more task added. Number two, any piece of hard metal the exact width of your saw plate or slightly narrower ground straight will work. A scrapper plate will work fine if hit with a hammer that won’t beat it up.
Jim

[steven c newman]

A Red Devil Putty Knife..the one with the non-flexible blade..