Recently there has been a lot of buzz in the woodworking community about the new Festool Domino joinery system. If you have not yet seen this system, it’s kind of like a Biscuit Joiner on steroids. However, different from the small circular blade on a Biscuit Joiner that cuts a football-shaped groove, the Domino cuts a rounded mortise with a router-like bit. The unique aspect of the Domino is that the bit both plunges into the work and also oscillates from side to side creating a very clean and precise mortise. Just like a Biscuit Joiner, the Domino is used to mortise both work pieces that are to be joined. The Domino joint is completed the by gluing loose tenon stock (specifically designed and supplied for the system) into the mortises.
This system has a lot of advantages. Some of the major ones are:
- Joinery, layout and execution are fast and straightforward – just mark the center of the mortise on each work piece and cut
- Work pieces can be cut to exact lengths – there is no need to add extra length to account for the tenons on the ends of pieces
- The mortises need no additional work, they are very clean and the loose tenons fit snugly into the mortises
- The joints made with the loose tenon stock are much stronger than those made with biscuits. In fact, loose tenons create a joint that is arguably as strong as any traditional mortise and tenon joint
- Making multiple mortise and tenon joints where required for strength is as simple as laying out and cutting another mortise in each work piece
- Unlike with biscuits, there’s no evidence that loose tenons will telegraph their shape to the surface of a work piece (this sometimes happens because biscuits swell when the get moist with glue – if the surface above them is sanded or smoothed prior to them drying out, a depression in the shape of a biscuit will often show up above the joint on the surface of the work piece)
So, with all of these advantages, why would you use anything else? This seems like the holy-grail of joinery! Well, if you have the means to purchase the Festool Domino, I would say: go for it! It looks to be an extremely well-engineered tool that excels at what it does. I may even add one to my shop in the future. However, if you are looking for loose tenon joinery on a budget, you should realize that there are alternatives. In fact, I have been doing loose tenon joinery for years using a basic plunge router and a simple jig.
Loose Tenon Joints on a Budget: The Router Jig
I often use loose tenon joinery in the construction of furniture projects. The system that I use involves a basic plunge router, an edge guide for the router, an upcut spiral mortising bit and a shop made jig. Because most woodworkers already have a plunge router and some scraps around the workshop to make a jig, this technique can be accomplished very economically. Better yet, all of the advantages of loose tenon joinery listed earlier are also realized when using this system.
The jig that I use for cutting mortises with the router is a relatively simple affair. It is adapted from a jig in the book: Router Magic by Bill Hylton. As shown in the picture, the jig is basically two pieces joined at a ninety degrees. The horizontal base component is for the router to ride on and the vertical riser component allows the jig to be clamped to the workbench. The work piece is secured to the jig with a toggle clamp that is mounted on a component that is attached with basic hardware through slots to allow for variable sized work pieces.
The only other components of the jig are lateral stops on the top that limit the travel of the router. These stops have a slot down the middle to ride over a piece of 1/4″ dowel for alignment. In the picture you can see the stops and a center line that is is scribed on the horizontal base for aligning the workpiece to be mortised.
Using the Router Jig: Marking and Alignment
The router jig is simple to use. Once I know the location and size of the mortise to be cut, I can mark the work pieces. In this example, I have two pieces acting as a Rail and Stile in a frame, though the same ideas apply to other kinds of work pieces.
I mark the Stile by striking a line indicating the center of the mortise and I align that point with the center line on the jig. Then, I can mark the corresponding Rail by marking its center from that point while aligning the edges of the two pieces.
You’ll also notice that on the Stile I’ve marked the extents of the mortise. This is only necessary on the first mortise. Once the stops have been set, only the center line of subsequent mortises will need to be marked. This feature makes the jig very efficient to use to cut batches of the same sized mortise.
Using the Router Jig: Position the Bit and Set the Stops
Before you can cut a mortise with the jig you need to set the location of the router bit and then set the stops.
To position the bit, I put the edge guide on the router and position it to ride against the back of the jig. Using the edge guide adjustment I position the bit roughly in the center of the thickness of work piece – it does not need to be exact, as long as I keep the same side of the Rail and Stile against the jig, the joint will be aligned when completed.
To set the stops I align the edge of the bit with the marks on the work piece that indicate the extent of the mortise. On each side I slide the stops against the edge guide bars and tighten the hardware to secure the stops. A this point, I’m ready to cut a mortise.
Using the Router Jig: Cutting the Mortise
Cutting the mortise is straightforward. I set the depth stop on the router to about 1/16″ more than the desired mortise depth (this extra space is to allow for a glue reservoir) .
I begin with the router against the stop closest to me. I cut the mortise by taking passes at a depth of about 1/4″. I continue making passes until I have reached the final depth. The advantage to using an upcut spiral bit on the router for this operation is that it is designed to plunge directly into the work piece and it also pulls the chips up and out of the mortise keeping the bit cooler as it runs. This results in a very clean mortise with precise edges and smooth walls.
Of course, this routing operation is the same for the Rails as it is for Stiles except for the orientation of the work piece. As I mentioned previously, once things are set it is as simple as aligning the centerlines, clamping the work piece and routing away. No further measuring is necessary!
Loose Tenon Stock
I usually make the loose tenon stock from scraps of the project that I’m building. I first cut some stock to the desired width of the tenon. The stock is then planed down to the diameter of the mortising bit. I usually use 1/4″ thick tenons for general joinery (in 3/4″ thick stock) and 1/2″ thick tenons for heavy duty applications – the only limit is which router bits you have on hand. At this point the tenon stock has square edges but the router cut mortises will have round edges. To remedy this, I simply pass all of the edges of the tenon stock over the router table with a round over bit installed (1/8″ round over for 1/4″ tenon stock and 1/4″ round over for 1/2″ tenon stock).
This may seem like a lot of work but it is actually very quick to do. I usually make a batch of tenon stock all at once in long sections so that individual tenons can easily be cut off to the desired length. Any remaining tenon stock can be used for future projects. Once the loose tenons are cut to size, I usually sand a quick chamfer on the edges so that they enter the mortises without issue.
The Completed Loose Tenon Joint
Once the matching mortises are cut into the two work pieces, the loose tenon is inserted and the pieces are dry-fitted. If all is well, I can spread some glue into the mortises and on the tenon and clamp the joint until dry. Because there is such a close fit of the tenon and the mortise with this method of joinery, not a lot of glue is necessary. I’ve noticed that if I’m careful I get very little glue squeeze-out. So, any cleanup is minor.
As long as I am diligent about referencing the appropriate sides of the work pieces against the jig, I have very little sanding or scraping to do to level the completed joint. The photo shows the results.
As you can see, this simple system has many of the advantages of the Festool Domino. The one thing that it lacks is portability. The Domino has the advantage of being able to be taken directly to the work pieces, whereas with this system the work piece must be taken to the jig. However, for the investment of a few hours time to make a simple jig, I think that this system performs very well.
As always, please contact me at firstname.lastname@example.org with questions and also please leave comments here using the comments link at the end of the posts.
In the comments, there were a couple of questions regarding the routing of the rail with the jig. So, here’s a picture of a routed rail in position in the jig.
As you can see the jig component with the toggle clamp is rotated to be in a vertical position. The clamp bar is attached via a couple of additional T-nuts in the jig to accommodate this (they were hidden from view in the original pictures). Hopefully this clears things up.