Tenon cutting sled

[Greg Guarino]

I designed mortise and tenon joinery into my next project, which means I am currently figuring out how I'm going to make both. I don't have a table saw.

I intended to make the tenons with a handheld router, a pattern bit (or maybe a guide bushing) and a jig that consists mostly of a board with a rectangular hole in it. In fact, I built a prototype which worked.

But I got to thinking that I'd need to clamp and reclamp and clamp and reclamp and ... you get the picture. One day I had another idea, a take-off on a crosscut sled.

[scroll right for more angles]

It's basically a sled with a steel guide that fits into the miter slot of my router table. The guide is set into a dado in the bottom of the sled. The sled has a slot down the middle that's the width of the bit (3/4"). It also has an adjustable stop that sets the length of the tenon.

It was pretty easy to build, and so far it seems to work pretty well, with two possible caveats. I need to remake the stop, it doesn't sit quite flat on the surface if the sled, which introduces some imprecision. I knew that as soon as I made it, but I wanted to see if the method would work at all before I improved it. I may also make the stop with thicker stock.

The second caveat is that I have only (so far) tried this method with about a 1/8" depth of cut. But I think it might still be faster to do it this way even If I have to make two shallow passes to remove more material.

It worked nicely at that depth. And quickly too. I wasn't that careful about cutting my test scrap and it came out well. Even the short sides cut nicely. The router bit has a tendency to pull the work *toward* the stop, which wasn't really a problem. I have so far avoided adding toggle clamps; if it works well enough holding the work by hand, I won't.

The one other tweak I think I'll make is to cover the back of the slot with a piece of something hard like maple, so I can't get absentminded and cut into the heel of my hand. That's not the natural place to put either hand, but I try to be safe.

[whit3rd]

I've expanded on that idea, with a wedge-operated vise/clamp to hold the board end in that rectangular hole. It's pretty quick to put the board loosely in the clamp and adjust the end flush, then tap the wedge to tighten. The vise is a 3-side plywood box, one wall of which is the fixed vise jaw (cement a bit of fine sandpaper on it for grip). Then two sidewalls get a (roughly) 2x 5 aperture, through which you put a points-left and points-right wedge cut from a 2x4.

Here's pix:

The board on bottom is for clamping the jig (usually to the bed of my table saw). The steel piece (Unistrut) is a screw-adjusted router fence.

It's near perfect for a sliding half-dovetail (position board, tap the wedge to clamp, and make a single cut). The wedge (and the bracing behind the fixed-jaw plate) will flatten a cupped board for accurate thicknessing, and a bit of springback just makes the half-dovetail fit tighter.

[Greg Guarino]

I'm finding the geometry of your jig a little puzzling. The pictures are pretty small. I think I can imagine how such a design *could* work, but from the angle in the pictures, I don't see where the work goes. Presumably through the front, but then how do the wedges hold it in?

In any case, judging by my quick tests with some oak 1x3, I think I can use my jig without clamping at all. It looks like it will work well, unless it is just on its best behavior while I'm still working on scrap. :)

[whit3rd]

Maybe you should expand the pictures; it's slow, but there's pixels to spare. The whole jig clamps to the top of my table (or table saw) and the workpiece comes up from the bottom, roughly centered in the rectangular cutout.

You can see the edge of the fixed plate in the cutout, and on bottom view it's the plywood chunk in the groove, with a 2x4 brace glued on... Fixed plate-workpiece-nonsliding_wedge-sliding wedge is the order. The cutout plate on top is where the router rides, it does obscure the other parts...

I don't have a thicknesser, and the prospect of trusting the cut from two sides of a board to get the right edge thickness, is daunting. Once I register the jig fence accurately to the fixed plate, and clamp (flatten) the possibly cupped board, a single router pass makes an accurate tongue or half-dovetail. I still have to cut the board end square, and position it flush with the cutout plate.

To do a tenon, one would clamp the board, router pass against the fence for one cheek, then make a second cut with a false-fence (spacer) of size fence_spacer = cutter_diameter + tenon_width

I haven't done that yet (it'll probably chew a bit of the fixed plate up).

[Greg Guarino]

Ah. So the work piece is held in the jig vertically?

I hadn't thought of that. I'll be using S4S lumber, and should be able to get the rails for whole project out of a small number of pieces, maybe 4. I'll be sure to check that the thicknesses are consistent.

[whit3rd]

Oh, yes, of course. The alternative was to slide a vertical board held against the fence of a router table (very awkward: better to fix the board and slide the router). This was for half-dovetails, the cut with a router had to have the router spindle parallel to the grain direction.

Now that I think of it, an edge-up clamp jig could also be used with a Skilsaw (or the smaller battery-powered saws), with some slight adjustments to the design. Saws cut quicker than routers, straighter (with wood on both sides of the cut). I wasn't thinking of tenons, though, at the time it all went together.

[John McCoy]

whit3rd wrote in news: [e-mail]:

For doing sliding dovetails, I can see you'd have the board vertical (altho I don't see holding it against the fence as being especially difficult, if you have a reasonably tall fence and a push block).

For tenons, tho, I'm a little lost why you'd need a jig if you have a router table. Just set the fence at the right distance for the tenon length and lay the boards flat on the table. If the tenon is longer than the width of the router bit, either move the fence or put a spacer on, or even freehand the end (carefully!).

John

[Leon]

Nice jig but I have always simply used the router table fence as the depth stop and a square piece of plywood to square and push the work through. This affords me the ability use any bit in my router table and gives me a exact match back up for any shape bit to prevent tear out on the back side of the cut. This is especially helpful when using rail and stile router bits.

[Leon]

I agree but typically you need something to keep the piece square to the fence when feeding. I use a square piece of scrap plywood indexed against the fence.

[John McCoy]

Leon wrote in news:NJWdnbJYR- [e-mail]:

Good point, and I do, in fact, use a square piece of scrap as a pusher whenever I'm routing an end. It's such a routine thing it didn't occur to me to mention it.

John

[Leon]

;~)

[Greg Guarino]

I thought of that. And in fact, a couple of years ago (when I was even more ignorant) I did that to rout spline grooves in the ends of my panel door rails.

But I didn't feel that good about it; too many things that can move in ways they shouldn't. This jig gives a guy like me, whose "hand skills" may be lacking, a nice secure way to keep the work square and to set the proper tenon length.

But you've got me thinking about the tear out. It wasn't a problem on any of the 4 test tenons that I cut, but now I'm thinking that I could clamp on a sacrificial backer piece for use with shaping bits, should the need arise.

[whit3rd]

I like using knotty boards, and recycled wood (often cupped or of uncertain or mixed thickness), and a cupped three-foot shelf board wouldn't get an accurate cut on a router table. A four-foot board would hit the basement ceiling.

As for tenons, I usually do those with a table saw, in one of the usual ways... but there's a recently-acquired battery circular saw that might get a trial on tenons with the jig.

Roy Underhill showed a two-screw vise that has similar function to this clamp/jig, but he wasn't exploring the power-tool options. I've also considered making a cutting-gage variant, to start my half-dovetail with a clean woodfiber slice (there's a lot of edge cleanup otherwise); the gage stop has to be pretty wide to bridge the open throat of the jig.

[Swingman]

What I like about my old Benchdog router table top, it takes my table saw miter gauge:

A fence and a miter slot combination, a classic methodology for table saw or router table for both safety and repeatability.

[Leon]

What I don't like with that method is setting the fence to be parallel to the miter slot, especially when sneaking up on the length of the tenon. I still prefer the square piece of plywood to reference off of the fence to push the work through.

The miter gauge Works great on the table saw however, I have made countless cuts to make tenons this way.

[Swingman]

Never had a problem with that. I simply use the squared end of the backer board, that is attached to the miter gauge, to set the fence parallel to the miter slot from one end of the other.

Works just fine, unless your fence is not flat, which means you would have been screwed to start with.

Just like when making tenons on the table saw using a miter gauge, the first pass already sets the length of the tenon.

[Leon]

I guess I could use a square to keep the fence perpendicular to the miter gauge fence while adjusting the fence. With the TS the fence is self squaring to the miter slot so there is no issue of the fence locking perpendicular to the slot.

Either works as well as the other once set up but I figured the fence set up on a router table would be a bit more finicky, to get it parallel, and to have the precise location set.

I typicality set the fence to the correct location then butt the sacrificial fence on the miter gauge up to the fence.

[Leon]

By all means, use what you are comfortable with. I was just sharing how I always do it. :-)