Friday, September 3, 2010

The Hammer Eye Joint, sort of...


I used to have and enjoy the Fine Woodworking books that compiled all  of their readers tips and tricks. One of them that really caught my eye was the hammer eye joint cutter submitted by some fellow named Dave Sawyer from Vermont. At that point, I'd never heard of Dave and never come close to making a chair, but something about this joint intrigued me.

The Hamer Eye Joint, sort of

Basically, the joint is like that which holds a hammer head on the handle. The hammer head has an hourglass shaped mortise and the handle tapers on the bottom of the tenon and is flared with a wedge on the top. This creates a mechanical lock that won't let the hammer hear move either direction. Brilliant, and it works in chairs too!
The Shouldered Tenon
One of my goals has been to build a chair wherein the glue is an afterthought, a sort of belt and suspenders approach. Even once the glue has turned to dust, I'd love my chairs to stay tight.
 The reason that I say that it's "sort of" a hammer eye joint, is that I've begun using it, but with more of a shoulder at the base than a taper that I'd ream. The shoulder, which you see int he photo above, is made with a simple cutter, like a straight pencil sharpener (I'll show how to make it next).
  
Measuring the Spindle
To get the shoulder line in the correct spot on the tenon, it's vital to get an accurate measurement of the length of the exposed spindle. Here you see my recent student (and guinea pig) Peter measuring the length with some taped together bbq skewers (is there anything they can't do?).

Once the tenon is cut (we'll go into this later), all thats left is to flare the top of the mortise with a file, only the end grain portions, so that you have an oval that the wedge will fill.
Notice the Gaps

When done correctly, the shoulder on each spindle stops the arm as you tap it down, and in the correct position. And then the wedge seals the deal.

The Flared Tenon End
Once locked in place, and combined with the moisture swelling of the superdried tenon, it's as solid as can be. This is especially desirable on the short spindles, where the thin arm offers very little glue surface and the joint takes a lot of stress through use. Of course, pinning the tenons is also a fine solution, but I think the results justify the little extra effort it takes to make this joint. Actually, I've found that it cuts down some of the spindle shaving time, so it's a win win.

Here are a couple of recent students with their finished chairs. I'll be making a few announcements soon about my teaching schedule and classes. Thanks to both of these fine fellows for their help experimenting with this joint.

Peter Nissen
Mark Foehl


1 comment:

NagaRaj Raj said...

The hammer head has an hourglass formed mortise and the cope with tapers on the lowest of the tenon and is flared with a wedge on the pinnacle. I'm working at Outdoor Advertising Services in Coimbatore This creates a mechanical lock that won't allow the hammer hear flow both direction. excellent, and it works in chairs too. hammer eye joint, is that I've begun the usage of it, but with greater of a shoulder at the base than a taper that I'd ream.