Thursday, October 10, 2019

Making the Tapered Tenon Cutter

Last time I wrote about making a tapered reamer that will enlarge and taper a cylindrical hole.  To go along with that, you need a way to taper a tenon that will fit into the hole.  This post will describe how to make the tapered tenon cutter.

I squared up a 2" thick piece of poplar, marked a location on top and bottom and bored a 1/2" hole.
I had drawn (poorly) several concentric circles before boring the hole.
Note the vertical reference line - there's one on back, too.
The next step was to taper the hole using the tapered reamer.  The concentric circles that I drew were to guide me in keeping the tapered hole as straight as possible through the workpiece.  This is not really necessary for the tenon cutter to work properly, but it's good practice and it might help me to make the tapers straight rather than on an angle to the axis of the spindle.
I had run the reamer a little more than needed - the far end was reamed to 11/16"
and the large end just under 15/16" diameter
From the point where the vertical reference line meets the bottom of the 15/16" circle, I drew a line to the lower left at about 15°.  After repeating that on the other side for the 11/16" circle, I sawed out the angled waste and smoothed the sawn surface with a chisel.
Didn't get any photos, thought I'd try describing with a Sketchup model.
The lower left triangle gets sawn out.  I sawed an extra 1/4" to the right of the
vertical reference line to add an "escapement".
I also sawed a flat area parallel to the newly sawn surface - a guideline can be seen under the ruler two pics above.  This was to give a parallel surface for clamping a blade to the tenon cutter.
Here's how the blade gets clamped to the tenon cutter
I'm using the iron from a spokeshave to cut tapered tenons.  I know some people will put a radius on the leading edge of the iron so that it doesn't gouge the tenon stock.  I still need this iron in my spokeshave, so I couldn't do this.
A closer pic from a different angle showing where to set the iron
I roughed out a piece of poplar to an approximately 7/8" diameter, small enough to fit into the big end of the tenon cutter, and made a test cut.
Ready to test the cutter with a 7/8" poplar dowel
Making tapered tenon shavings
It's hard to know whether or not I had the dowel 90° to the tenon cutter.  I've gotta think about how to ensure that.  If you hold the dowel off-center, then the axis of the tapered portion will be angled from the axis of the straight portion of the dowel.

I tried the tapered tenon in a hole that I had bored and reamed.
Nice and tight in the large end ...
... but a little loose in the small end
So I modified very slightly the bed of the cutter to remove a little more from the large end of the tenon
It took a couple of iterations, but I got a nice tight fit of the tenon in the tapered hole.  I still need to do a bit of refining, but I'm almost there.

Just a note: this is probably very obvious to most of you, but I hadn't thought it through until I made these things.  You'll need different tapered tenon cutters for various diameters of spindle stock being tenoned.  For example, the thicker legs of a chair might be 1" diameter at the start of the taper, whereas the spindles for the back of a chair might be 5/8" at the start of the tenon.  They'll need separate tenon cutters, even though the same reamer can be used for both sizes.  So far I've made two tenon cutters - one for 7/8" dowel stock and another for 1 1/8" stock.

Another note: The YouTube channel "Pask Makes" has a couple excellent videos on making a tapered reamer and tapered tenoner.  Much of my method came from those videos.


  1. Ah Pask Make. I love his Scrapwood challenges.
    I would had thought you wanted some looseness on top in prevision for wedging?? Or you rather keep it tight, the more pressure on the legs, the tighter the joint scenario?

    Bob, probably overthinking it :-)

    1. That's an interesting point and I hadn't thought about that, Bob. But I'm pretty sure these things are made for a tight fit without a wedge. The wedge will have to compress fibers to fit in there. Just have to make sure the wedge is oriented perpendicular to the grain of the mortised piece.

  2. For the blade Planner thicknesser used HSS blades cut with an angle grinder two slots for the fixing. I use 12g Timber screws 5/16 hex head large flat flange,holds the blades, very securely. I have used these blades many times to make rounders, from 4mm up to 50 mm at no cost only time Richard Bingham UK

  3. Matt,

    Good work. Are you planing on your tenons to protrude? BTW, I've split a seat blank with the wedge oriented cross grain. Go figure,


    1. I'll aim for slight protrusion to trim flush later. Gotta be careful - it's easy to taper too much of the tenon and have it protrude way too far.

      Oh man, that's got to be heartbreaking to split a seat when you've done everything by the book.