Overhead Router Tennoning Jig


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Established Member
31 Jul 2005
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North Somerset
Right then. The idea for this tenon-cutting jig for my router came about some time ago when I came across a very similar idea for cross-cutting with a handheld portable circular saw (from a Stanley book on Storage and Shelving).


The idea is that the router (in traditional overhead position) runs along these two guide rails (in this case, made of 2mm thick angle iron) and will cross-cut one face of a tenon, nibbling away from the end grain (feeding timber from left to right) until you reach your marked line (a stop can then be fixed to the right of the rails). Then, flip the timber over for the other face and repeat, working your way towards the stop.


It is very important that the timber is positioned against the rear timber fence, due to the direction of which the router cutter rotates. Otherwise, you know, the cutter might suddenly catch the timber and try to fly away! Unless, of course, you find it easier to pull the router towards you; in which case, you would only then have the timber against the fence nearest you. But in my situation anyway, I have used the rear fence only as a reference for setting the guide rails at 90 degrees.


As you can see, I am using a quick-grip clamp to hold the timber - although I plan to replace this with a couple of toggle clamps fixed on top of the rear fence.

The overall dimensions of the base (18mm MDF - chipboard, ply, etc. will also do) are 600mm long x 300mm wide. This gives me a comfortable 260mm working space between the front and back fence (58mmx19mm) - which matches the maximum capacity of my planer-thicknesser, just incase. It also allows me to rout several tenons at once (depending on the width of the rails to be cut, of course). :wink:


In order to get the correct working height below the guide rails, I took the maximum given plunge depth of my router (60mm) and subtracted the thickness of the angle iron (2mm), which left me with 58mm - plenty, as I haven't yet come across a job with rails any thicker than 2". :)

I'm not sure about the angle iron though. I've cleaned it up and even waxed it to ensure it doesn't make a mess of my router's base (I may also make a spare one from acrylic), but they aren't terribly true along their short length - although, arguably, it's not something I cannot clean up with a shoulder plane.



I made these test cuts with one of Rutlands Tornado 3/4" twin-flute straight cutters, which leave a very clean finish, but they are only 1-1/4" long and therefore stands just over an inch above the base of this jig.
It may well be okay for the tasks I have ahead of me, but I'd like a longer cutter (2"+) and I'm looking for suggestions please?

Trend and Tornado seem to do them but they're only 1/2" in diameter. Silverline do a 3/4" one (Toolstation) but I'm unsure of the quality. You can understand my desire to have a wider cutter when you think of the number of passes it would otherwise take to rout a 4" tenon! :roll:

I hope you have all enjoyed reading this and I'd like to think that some of you will find this idea very interesting indeed - hopefully, some of you will go away and develop on it! But I'm equally open to criticism all the same.! :wink:

Thanks for looking. :D
hi olly'

i have been using something like this for a long time now,
you need a spiral cutter with an upward shear you can get these from
you can also use it to put a miter on the end of timber for boxes and the like

good jig

Very nice Olly

I used those angle irons long time ago, while in Japan but I was not satisfied with the smoothness. They have some radius inside so, I was getting some bindings...

I would like to share with you what I did and maybe it will give you some ideas...

I added some pictures...otherwise you would end-up making sewing machine with my explanations...


That's the Crosscut box, plywood rails with MDF screwed under to support the saw base


I clamped a triangle and screw one guide rail

Clamp the other guide (very light) and screw it



I made a long base on the router


By changing the position of one guide...

I get guide for the router

Another idea is to screw only 2 rails (without the support)

And use the router with a long base but, the base have to be long enough to "cover" both sides of the box
Nice idea Niki.

Why didn't you make the base for the router the same size as the saw base ?
No need to alter the guide then.

mrbingley":2ojdcj4w said:
Nice idea Niki.

Why didn't you make the base for the router the same size as the saw base ?
No need to alter the guide then.


Because.......I did not think, and that's the reason...

But, I have many excuses... :):):)

Thank you Chris, maybe it's about time to make another, wider base (this base fits my rabbet jig).

Thank to everyone for their replies and comments. And thanks also to Niki for another in depth explanation of a great idea! I like the way your base plate is sandwiched in to prevent the tool from jumping back at you.

I'm still not sure about the aluminium angle though. I do have some 6mm acrylic lying around, that looks like it may be strong enough - but it might be just a tad too thick for my liking. I want to keep it as thin as possible to maintain maximum cutting depth. Of course, this compromises the strength...

My other idea is that I find some straight, flat lengths of steel and set them up to use my largest guide bush.

I'm still open to any other suggestions of course! :wink:
Hi Olly

If height is important, you can make the rails of 3 or 4mm plywood and glue (and screw) to the guides (my guides are 18mm plywood) or you can screw 1 or 2mm steel rail.

I think that if you glue the 3~4mm plywood rail to the guide, it will be strong enough to support the router and you can omit the router base plate and get the maximum height (depth).


Thanks again for the excellent ideas Niki, but this weekend - when I should have been busy starting my competition entry :roll: - I got busy and made myself a sub-base from 4mm acrylic.


Of course, this has been drilled out to suit my router, using the existing sub-base as a guide. This also helps to prevent the loss of any cutting depth - I reckon now that, with a 63mm long cutter, this'll be just perfect. :)

I don't know about spending £50 on a Wealden cutter just yet though! :? I've ordered one from Axminster's Perform range, for the time being. I didn't have any tearout from the shorter Tornado cutter and, if need be, I reckon I can get away with knifing the shoulder lines anyway.


The acrylic base is referenced against a length of straight timber (in this case, southern yellow pine) set at exactly 90 degrees to the rear fence. This allows me to line up the shoulders for the finished cut and also to cut longer tenons in one go; one side at a time, of course; but I don't need to slide the timber along once it's set. :wink:

Other lengths of scrap timber were added to give the 4mm acrylic extra rigidity - and it works.

Now, all I need to sort out - aside from my competition entry!! :? :oops: - is a method of holding the timber in place.

I'd like to have something which sits on top of each fence, but would a toggle clamp have a suitable depth for this?

Thanks for looking, guys - and for your help. :D [/u]