Tuesday, October 5, 2010

Making a Tenon Shoulderer

As I promised a few weeks back, I'm going to show how I make my tenon shoulderer for the semi hammer eye joint. I have been using this joint a lot and I am sold, it's just good chairmaking, and in some ways  it's actually faster.

But first I have a few announcements,

I will be teaching a class at Highland Woodworking in Atlanta this month. I highly recommend this class because of the format. It will be a two day seminar where I build a chair and demonstrate all the techniques that the class will cover and more. Then it's a hands on 5 day chair class. Often, I find that students have trouble conceiving of the whole process until they have built a chair and this can make each step a bit bewildering, so with the info up front, I'm looking forward to everyone getting that much more out of it. I hope to see you there.

I've also built a new web site (have you wondered where all my computer time has been spent lately?) Check it out at the usual address www.petergalbertchairmaker.com.
Of course it's not finished and some of the images and text need some work, but it has been useful in helping me define what I am trying to do with my chairs.

Also, on the site, you'll notice that the "Classes" page has some new information about my teaching. Lately, it seems that I've had trouble keeping up with the number of folks who want to come work with me, so I've added a 4 person course that I plan to teach twice next year. The first class is on June 6th and will be a fan back class. I will have a full time experienced assistant and we will shoot the works while building a lovely chair. Because I've decided to limit my one on one courses, I encourage anyone interested in taking the group class to contact me soon.

Now, on to the tool,

As I covered in the previous post, this isn't a true hammer eye joint because I don't ream the mortise on both exit and entry. It's really just a shouldered tenon that gets flared.  Below are a couple of tools that I've made for different sized tenons. You can see that they operate with a spokeshave blade and a block of dense hardwood.

The tool pictured in the front has some fancy adjusters that I made (just some bolts and washers really) but I've made plenty of them without as well. The first step is to choose the size that you want the mortise to be, here I am using a 3/8ths mortise. I selected a piece of hardwood about as wide as my blade, for convenience, because as you'll see, it isn't necessary.

Here is the layout for the bed angle and clearance for the chips. One of my goals is to keep the throat of the cutter tight to reduce tearout on the tenon. Start with a vertical line to the top of the hole and then make a line that contacts the top of the hole at a 30 degree angle. Then draw another line at that angle the thickness of the blade below the line you just drew. This is the actual bed for the blade.

Here is the layout for the tapered hole in the block. I've randomly chosen 1 inch in to be the transition from the taper to the straight portion of the tenon.

To ream this, place your reamer in the hole and measure back 1 inch. I put tape there to be clear. Then simply ream until the tape contacts the side of the block. A word about reamer angles. the greater the angle, the greater the stopping power of the shoulder, but also the more obvious, it's up to you.

Here I've cut out the bed angle on the bandsaw.

 When you put the reamer in the hole, it should stop making contact 1 inch in.

Now it's time to shape the blade. The blade only cuts the tapered part of the joint, so I simply measure in 1 inch and grind away material to create a transition in the middle. I find it helps to curve the blade edge at the point that the spindle enters the cutter to help prevent any tearout. I actually blunted the edge of the blade in the straight area, it doesn't make any contact anyway.

In the next post, I'll show how to put it all together and make the joint!


Andrew Jack said...

nice. so far so clear. i like that the blade only really makes the shoulder, rather than cutting the tenon itself; well put. was that an appropriate semi-colon?

Peter Galbert said...

Thanks Andy,
we'll work on your punctuation later...

Andrew Jack said...

I'm finding that a steeper initial taper increases the incidence of tear out. The small Veritas cutters make such an abrupt shoulder by way of bedding the blade at a nice kinda compound taper-skew. Let's call that a Skaper. I may try it for kicks, but the insert might not play nice with the short grain on a wooden cutter.... Just some random thoughts.

Peter Galbert said...

Lemme know what happens, or we'll work with it when you come to play!