Olly Writes

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Simple Tenon Jig

Before I could start cutting any tenons on the side table I’m currently building, I needed to build a new tenon-cutting jig for my router table.  For the past two-to-three years, I’ve been happily using a jig designed by Steve Maskery (of Workshop Essentials), which has some great features and works very well with a ordinary, twin-flute straight cutters. However, my reason for building a new jig is that I want to be able to use my tenon cutter from Wealden but, my Freud router doesn’t plunge far enough…

So, I came up with two jigs!

Both are pretty straightforward to make, using scraps of 18mm MR MDF and hardwood (ash, in this case). They follow the basic design of a “push-board“; used to hold the workpiece square (or, at an angle) as it passes through the cutter, while preventing breakout on the rear edge. There’s a main fence (made from ash, here), which is glued and screwed to the 18mm base – though, based on past experience; once the glue was dry, I replaced all screws on the fence-side of the jig with wooden dowels (yes, you could say I’ve trashed a few straight cutters, in my time… :oops:). This is fixed at 90° to the running edge (which is lipped with a hardwood strip, for durability) and also pre-drilled for attaching a sacrificial softwood fence (this prevents the spelching), which can easily be repositioned or replaced when the time comes.

One of these jigs has a 6mm plywood base attached below, which provides a 100mm wide platform at the front (lined with 120g abrasive paper for grip), which is where the timber sits, firmly, as the ends are machined. The reason I made two was in case this idea didn’t work – in which case, I would always have a backup! 😉 Both handles are hexagonal in section and were hand-planed to shape (you could, of course, bevel these edges on a bandsaw or, very carefully, on a table saw). I didn’t want to waste any more time shaping a fancy plane or saw-type handle and my lathe (just like my mortiser) is currently buried behind four machines!

In practice, the new jig works very well. Adding the abrasive paper was certainly a good idea:

There’s currently no hold-down clamp as I fear the 18mm MDF base would flex too much under the tension (ply would be better, perhaps even 25mm thick). But, for small-scale furniture components like this, it does seem to work well enough, right now. You’ll also note from the above photo that clearance is sufficient enough for my to keep the guard attached to my table’s fence. It is very important that you “break-through” a false fence fitted to your router table – otherwise, if you’re using a two-part split-fence, anything less than the diameter of the aperture around the cutter can get dragged in (at least, without a clamp in place).

This is the jig I’m replacing, based on a design to be found on Volume 1 or 2 (I forget which!) of the Workshop Essentials DVDs:

I still think it’s a great idea and I would still be using it today, if only my router had an extra inch or so of plunge depth. I should’ve made the base from better quality plywood (this is ‘shuttering’ or ‘sheathing’ ply). This stuff wasn’t dead flat but, again, it was only what I had to hand, at the time. The addition of a hold-down clamp is an excellent idea and, with such a tall guide post, you can stand your rails on edge to nibble your  tenons down to the correct width as well as thickness (something you can’t often do with a toggle clamp). Where the base is in contact with the fence on both sides of the cutter, there’s no risk of the jig getting pulled in by the cutter and over-cutting your shoulder lines – my jigs are about 300mm/12in long so, provided I don’t try to bite off too much in a single pass, I’m hoping I would have this problem, either (again, this is where breaking through a sacrificial fence also helps).

But, on Steve’s design, the hold-down was fairly close to the table fence (meaning I couldn’t fit my guard) and the action of tightening the lever left your fingers within inches of the sharp, spinning bit. As you can see, I tried making another clamp head with a longer lever but, this didn’t seem to reduce this particular risk much at all. For longer workpieces,  I don’t see why you couldn’t add a second clamp alongside on this particular jig.

So, I’m now quite happy with my setup for cutting tenons and the results are looking good – perfect, 90° shoulders, first time! 8) Another critical point with any jig likes this is that your timber has been accurate prepared and is parallel, since you’re working off each face, in turn. For offset tenons though, you’d have to make one pass on one face of each component, reset the cutter, and then router the other faces (without ruining what you’d previously cut!).

Where a job comes a long and the components are too long to use with this jig, I think I’ll have to resort to using the bandsaw, like this:

For the latest updates on Side Table progress, click here.

Thanks for reading.

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