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.

butterflies.jpg

[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.

268472_240071966005006_100000066129747_1065359_1765298_n.jpg

[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.co...-table_01.html