Butterfly (Dovetail) Keys by Hand

[Steve Friedman]

Hi,

I have a question about attempting to insert a couple of butterfly keys into a slab top to support some large cracks and am not sure what tools I need to do this. I am not worried about the key itself, but the excavation part that the key fits into (not sure what that's called). There's plenty of information on doing this with electricity, but I would really prefer to try these by hand. Since the excavation is typically done with a power router, I naturally assumed that a router plane would be the tool of choice and was about to get one. But, I think that's wrong. It seems that the excavation is typically done with chisels.

So my question is what tools I want to be able to do this by hand? For chisels, would a dovetail or skew chisel help because of the corners? Do I still use a router plane to clean up the bottoms? If yes, would you recommend a small router (instead of a full sized one) to have better control?

Thanks in advance for any help.

Steve

[Jack Curtis]

You can certainly start with chisels and use them to take out most of it; but you'll find it easier to level the depression with a small router plane. Piece of cake. Not a bad idea to drill to the depth you want in several places and use those holes as indicators of depth.

Jack

[Dale Osowski]

When I waste away for a butterfly with hand tools I use a Forstner bit and clean up corners with chisels and files.

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[Rob Fisher]

I would call the excavated hole a mortise. And I would rough it to depth with chisels (or maybe drilling) and finish the floor with a router plane. This is definitely a good use for a router plane.

[Jessica Pierce-LaRose]

Obviously, clean work is the best work, but how clean to the "floors" of these actually need to be? It seems like all the strength of this device comes from the lateral (that is, parallel to the tabletop) direction, and results from the tight fit of the wood and the tapered wedge action. If the joint on the floor was doing the work, a straight-sided rectangular shape would work fine, but doesn't glue not hold as well against shear loads? It seems like the smooth bottom is really just get a good glue surface to aid in keeping the key from accidently popping up? I don't know - i have no experience with these, but couldn't you get away with a little bit of a rougher bottom on one of these? I'm not saying I'm right, just curious and asking.

That said, with a little care, I've been able to make shallow, flat bottom mortises somewhat akin to this for simple inlays using a chisels. I've smoothed the bottom by hand, carefully, with the bevel down. Drilling holes, as Jack mentions, to be able to see the final depth approaching works quite well. With a little care, I've been able to get quite smooth bottoms like this, although a router plane is much easier for the final trim.

As to which size router plane to get, you really have to look at the size of the keys you want to make, and see which sized blades will work well for it, and base your decision on that, although I think both LV and LN offer smaller blades for their full size router planes now.

[Steve Friedman]

Thanks for the feedback. Would you suggest a small router plan as opposed to a regular size one? Also, would this be easier with a thin paring chisel as opposed to a regular bench chisel? I'm just picturing it being really important to control the cutter to avoid overshooting the lines.

Thoughts?

[Bill Houghton]

Thanks for the feedback. Would you suggest a small router plan as opposed to a regular size one? Also, would this be easier with a thin paring chisel as opposed to a regular bench chisel? I'm just picturing it being really important to control the cutter to avoid overshooting the lines.

Thoughts?

Regular bench chisel should be fine - in fact, a thin paring chisel might be too light. Regular or small router plane depending on how large the butterflies are.

[Kent A Bathurst]

When I cut mine.......Famous Blue Tape on the field. Hold the key in place, and carefully trace around it with exacto or marking knife. Pull the tape from the key area. Very, clear, clean line defined by the remaining tape. I find it much, much easier to see that line than with the exacto or marking knife score only, and the score is still there to help register the chisel.

Then, use a chisel to define a shoulder all the way around the mortise. Keep working back from the line to cut a deeper shoulder in multiple passes. Then - hog out the field. It is easy to stay clear of the edges, once the shoulders are defined. Plus - you need to stay away from the edges only at the table's surface - if you were to undercut the mortise a bit, or get sloppy, it'll never show.

For larger ones, I use lam trimmer, or my large router plane. For smaller ones, the large router plane is too big to be much help, and the lam trimmer doesn't really save a lot of time, so I will often go after those with bench chisels.

[Maurice Ungaro]

If the butterfly mortise goes all the way through, giving more lateral holding power, why would you need a router plane? (don't get me wrong, I want two of those myself). Is there something preventing you from making a through mortise - I've never done one of these types before.

[Jim Matthews]

If the butterfly key is for strength, it needs to be deep.

Orient the long grain of the key across the split (crossgrain). You could certainly pre-drill lots of little holes to get the depth established, and chisel out the waste.
I would start with some margin inside the edges and taper (thicker at the top than the bottom) so that the key can be beveled for best fit.

If you go all the way through, you could cut this with a keyhole saw and shape the edges with a rough file. That might be easiest.

Pictures of your progress would be nice to see.

jim
wpt, ma

[Steve Friedman]

Thanks for the advice.

Kent - How do you get the bottom on the mortise somewhat flat without a router plane? The small router planes aren't really deep enough (it's an 8/4 slab), but you nailed the issue - concern that the large router plane would be too clunky to be useful on smaller keys. In my case, I was mostly concerned about an inability to control it. LN has a 3/32" pointed blade for theirs and LV has the blades down to 1/8", but not pointed - I figured I could grind a taper into it.

Maurice & Jim - I never thought of having the key go all the way through the slab. I know it needs to be deep, but always assumed (yeah, I know) that the key didn't go through because that's the only way I have ever seen it done. I was planning to go around 2/3 of the way through the slab. If you go all the way through, wouldn't it be impossible to get a tight fit on both the top and the bottom? With tapering the key, the openings would need to be slightly different. The other issue is that the slab is around 42 x 42 of 8/4 walnut, so I will not be able to flip it without help. That would make it very difficult to try to fit both sides at once (unless I put it on edge). I suppose I could do 1/2 of the key from the top and 1/2 from the bottom, but that seems like more work than just dealing with flattening the bottom of the mortise. WWND? (What Would Nakashima Do?)

Thanks again,

Steve

[Maurice Ungaro]

I would think that if you are going all the way through, then you make the walls of the mortise as straight as possible. I have a piece of walnut that needs the same thing, but not as thick. My plan is to go all the way through, but before envy thing is laced out, or cut, the split in the board will be drawn tight with clamps. When inserted, the key should take the place of the clamps. ......I think....

[Dale Osowski]

George Nakashima's butterflies typically went 2/3's the depth of slab and often screwed in from bottom. You can get as flat of a bottom as you need by using a forstner bit. Use a guide block to rest the back of your chisel against for a clean wall cuts. Photo below will give you an idea of butterfly depth vs slab.

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[Steve Friedman]

Dale, great picture. I was just guessing at the 2/3, but am thrilled to see that Nakashima would have agreed with me.

[Dale Osowski]

Thanks, the last photo was actually of my first Nakashima inspired table: http://djofurnituremaker.blogspot.com/2010/01/cherry-coffee-table_01.html

[Dale Osowski]

Depending on location you can use the joinery to add butterfly:

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[Steve Friedman]

Thanks, the last photo was actually of my first Nakashima inspired table: http://djofurnituremaker.blogspot.com/2010/01/cherry-coffee-table_01.html

Wow! I assumed it was your table, but seeing the finished product is awesome. I also really like your coffee table (which is what I'm trying to build), but having problems deciding on the legs. Figured I would do the top first and then decide.

Amazing work!

Steve

[Dale Osowski]

Thanks Steve

Here is the latest table, not the best photos though: http://djofurnituremaker.wordpress.com/2011/09/25/a-quick-update-3/

[Steve Friedman]

Dale, very cool. Love your work and the distinctive styling on the keys. What wood do you use for the keys?

Steve

[Kent A Bathurst]

How do you get the bottom on the mortise somewhat flat without a router plane?

Well - I've never gone into 8/4. ~ halfway through 5/4 has been my deepest. Chisel[s] and patience. "Somewhat flat", or "flat enough" has been my goal. The deeper you go, of course, the harder it is with chisels - seems like you almost need a crank-neck chisel for that work. But - dead-nuts flat has never been essential IMO.

To be honest, if I was in your situation, I would probably get out the lam trimmer, run with 1/4" mill bit first, and then a 1/8" or 1/16" dia bit to get closer to the corners, and burn some electrons. Then, clean up w/chisels. So - that's not really what you wanted to hear.

[Steve Friedman]

Kent, thanks. I guess sometimes the truth hurts! I do have a Bosch Colt and a Dewalt plunge router, but hate using them. Even with the Colt, I never feel like I have as much control as I want for something like this - and I only get one shot! Never thought of trying a crank neck chisel. Have to mull that one over. Not sure how that would work with something relatively wide and shallow (compared to a mortise) and not rectangular.

Steve

[Jim Koepke]

It seems like the smooth bottom is really just get a good glue surface to aid in keeping the key from accidently popping up? I don't know - i have no experience with these, but couldn't you get away with a little bit of a rougher bottom on one of these? I'm not saying I'm right, just curious and asking.


I think this would depend on the glue being used. PVAs and some other glues are not good at filling and holding across a gap. Epoxies and some others can bridge gaps.

jtk

[Kent A Bathurst]

Even with the Colt, I never feel like I have as much control as I want for something like this - and I only get one shot!

This is the precisely the thought/concern that led me to the Famous Blue Tape solution......it is really easy to see where the edges of the mortise are. I have never had an issue, but at first I was stopping way too short. I still don't try to push it too close, though, and then I finish with a chisel & hammer.

[Dale Osowski]

Here are some photos of the process using a trim router. Once roughed out with 1/4" bit I cut to the line with a 1/8" bit. For some reason they posted out of order but you get the idea.

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[Jim Matthews]

WWND? Probably turn an apprentice on the problem... this is going to be a chore, no matter how you cut it.

My suggestion for a through saw is to give you a clean side that can be refined with a rasp or file.
Once you have the hole cut through, and straight, it would just be a matter of fitting the key.

Still - this is going to take awhile.

[Shawn Stennett]

I made some in a hall table that was 8/4, I only went 1/2 deep. I made my key and put a dab of super glue with accelerator where I wanted a key, let it dry and carefully traced around. Like Kent I did it lightly first and progressively went deeper to create a wall. Then took a chisel and carefully cut some waste away around the edges, then used a LN small router plane and got it to the depth I wanted. Every once in a while I would use my chisel and cut around the edges to define the boundaries so the router didn't want to go to far.

[Jack Curtis]

There are chisels and then there are chisels. After doing the initial work with regular straight chisels, I switch to two types, spoon bent and flat bent, both Japanese. Most crank necks have working ends too long for getting around a mortise like you'll need, although some of the Japanese have shorter blades. Here's a photo of a spoon bent:

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This is a Takahashi from Japan Woodworker. I use Takahashi, from a Japanese vendor because I prefer metric; but mostly I use Hiraide offerings instead.

Jack

[Steve Friedman]

Thanks Jack,

I actually have a Hans Karlsson dog leg gouge from Country Workshops, but it's way too big. Never thought about using a spoon gouge to do this. Obviously it needs to be much smaller and flatter than mine, so thanks for the lead.

Steve

[Jack Curtis]

I actually have a Hans Karlsson dog leg gouge from Country Workshops, but it's way too big....

Hmmm, maybe you could make super big butterflies? :) Those are great looking gouges.

Jack

[Steve Friedman]

I only have the big dog leg gouge, which has a sweep that's probably around a 3 and is almost 2" wide. But, I like the shape of the neck more than a pure crank neck chisel. After doing a little searching, it seems that the closest things may be the TFWW Ashley Iles dog leg and spoon flat chisels. Since I started in woodworking by learning to carve, I am much more confident using chisels and gouges than a router plane. On the other hand (if it wasn't obvious) I really want an excuse to buy a LN or LV router plane.

Steve

[Rob Fisher]

... Since I started in woodworking by learning to carve, I am much more confident using chisels and gouges than a router plane. On the other hand (if it wasn't obvious) I really want an excuse to buy a LN or LV router plane.SteveUsing a router plane is fairly easy. On the LV (which I own) you set the depth stop, which is pretty robust, and go to town. You can still adjust the blade up, with the depth stop acting as the final lower setting. A few minutes with a router plane and you will have it figured out. On a side note, how do you like the Karlsson dog leg chisel? I have been wanting one to work on some bowl carving.

[Tony Shea]

You really don't need much of an excuse to buy yourself a router plane. This plane is the most used specialty plane I own. And gets almost as much use as my common bench planes. There is no better tool at getting to surfaces parallel with each other.

I just made my own butterfly inlays, mostly for decoration in the bottom of a jewelry box I'm making. I will post a pic of it soon.