Fitting the Draw-bored Mortise and Tenons

With the mortises all cut in the workbench legs, I need to fit the tenons and drill the holes for the draw bore pegs.

As the tenons stand, each is at least 4″ long.  The mortises in the legs intersect, so inserting one tenon into its mortise would prevent the second one from seating all the way.  In order for both tenons to fit, they will have to be mitered.

To mark where the miter will have to be cut, I first inserted each tenon into its mortise.

Insert one tenon into the joint.

I then used a chisel to mark a line on the tenon at the point where it intersects with the other mortise.

Use a chisel or knife to mark the sidewall of the second mortise onto the first tenon.

With the tenon removed from the joint you can clearly see the line.  Material to the left of the line in the below picture needs to be removed at a mitered angle.   Why not cut it of square at this point?  Well, you could, but I’m going to drive some beefy oak drawbore pegs into this joint and the more material that is between the peg and the end of the tenon, the less likely it is to bust out the end grain of the tenon.  Also, the longer the tenon, the less racking of the joint is possible.

Remove the tenon from the joint and the line is visible.

I went round, stretcher by stretcher and marked each of the eight tenons.  I darkened the chisel lines with a pencil and using the 45° side of a combination square, marked the miter angle to be cut.

I used the 45° side of my combo square to mark where I needed to cut.

I used a tenon saw to make the cut and was careful to follow both lines.  I’m finding that hand sawing does improve with practice.  I just need a lot more practice.

Using a tenon saw, I cut to the lines.

Tenon mitered.

I cleaned up the cut a little with a block plane.  My main concern here was to softly break all the edges.  None of this will be seen once the bench is assembled so this is not for cosmetic reasons.  However, the gently rounded edges make it easier to insert the tenon into the mortise and helps prevent it getting caught up or binding as I put it together.

I relieved all the edges with a block plane to make the tenons easy to insert.

With all eight tenons mitered, I did a test fit.  This is great, I’m starting to see how it will all look together.

With all the tenons mitered, I did a test fit.

Next up is drilling the holes for the drawbore pegs.   I have bought several lengths of 5/8″ oak dowel to use for the pegs.  I spent some time at the hardware store picking out dowels that were of very straight grain and had no run out to the sides.  I cut them to 9″ lengths and tapered one end of each.

A couple of weeks ago I had the chance to stop by the Grizzly show room in Bellingham and picked up a set of large long drill bits in a wooden case. They are item number H7695. Ok… they’re not of particularly good quality, but what do you expect for only $17.  The brad point had some pretty serious burrs left on the cutting edge from the factory, but I used an auger bit file and had it sharpened to my satisfaction in only a few minutes. Once I had done this, the bit cut beautifully.

I had planned on putting two pegs in each tenon, but there just isn’t enough room.  The pegs have to be off-set from those in the adjacent mortise and tenon joint or they would hit each other.  As a compromise, I am going to put one peg in the tenons of the short stretchers and two pegs in the tenons of the long ones.  You’ll see what I mean here shortly.

To keep the holes nice and square to the legs, I started them on the drill press.  My press has a quill stroke length of around 3 7/8″.  This means that I cannot drill through the 5½” thick legs without adjusting the table mid-cut.

The 1st 3 1/2 inches of the hole are drilled at the drill press.

Not a problem.  I drilled the hole as deep as the press allowed and removed the leg to the workbench.

Drilled as deep and the quill stroke on my press will allow.

I then took a 5/8″ WoodOwl auger bit and mounted it in my favorite brace.  Since the drill press has started the hole and it is square to the leg, the auger bit will follow the established hole without the possibility of it wandering off course.

I put a WoodOwl bit in the brace to finish the hole.

I bored until the lead screw poked through on the exit side.  I then backed out the bit and completed the hole from the other side.  I repeated the process for all 12 holes.

I stopped when the lead screw just poked through the exit side.

You can see below what I mean about there not being room for four pegs in each leg.  I’m not sweating it, I think this will be strong enough.

One peg for the front to back stretchers and two for the left to right.

With the holes in the legs done, I needed to create the off-set holes in the tenons.  To do this, I reassembled the joint and added a clamp to hold it together snugly, but not super tight.  I used the same WoodOwl bit to mark the center of the hole on the tenon.  You just have to press the lead screw of the bit into the tenon enough to prick the surface and leave a mark.

After assembling the joint, I used the bit to mark the center of the hole on the tenon.

Since these are rather large joints and the hole goes completely through the leg, I marked the center of the hole on both sides of the tenon (from front and back).

A clamp held everything in place while I marked the tenons.

I removed the stretcher from the leg and was able to see the mark that I had made on the tenon.  I then made a second mark about 3/32″ towards the shoulder from the first.  I did this on both sides of the tenon.

Off-setting the mark towards the shoulder.

I off-set the mark by 3/32″.

Back at the drill press, I used the same 5/8″ grizzly bit that I used to drill the legs.  This hole needs to be drilled with some accuracy, so a brad point bit is very beneficial for this part.

I used a 5/8″ brad point bit in the drill press to make sure I put the hole exactly where I wanted it.

I carefully lined up the center point with the off-set mark and drilled halfway into the tenon.  I then flipped the tenon over and completed the hole.

I drilled halfway in from each side.

Once the joint is put back together, you can see how the holes mis-align.  When the oak peg is driven in, this joint isn’t ever coming apart.   Sorry for the poor quality of the below photo, but I think you can see what I’m talking about.

When put back together, you can see that the holes are off-set.

In my next post, I’ll cut the legs to length and cut the tenons on the top of the legs.

More soon.

– Jonathan White