Mortise and Tenon wood joinery is one of the most common ways of making woodworking jonts in quality furniture, timber framing and other forms of woodworking. In this video I am completing the other half of the jig making exercise by making a mortising jig. The mortise is this hole in which the tenon is inserted, and often glued or pinned, that go together to make the woodworking joint. There are many, many ways of making mortises from dedicated mortising machines, to using a drill press, cutting them by hand with a mallet and chisel, using a router and more. In this video we will be using the router and manufacturing a simple attachment that is easy to use, and not complicated to set up, to make mortise cuts for mortise and tenon joints.
Watch this and other similar videos on YouTube - https://youtu.be/G9rNbWB1jmc
To make the morise jig, I started off with a pices of 1/4" hardboard. I find this is better that plywood for this knid of a build because the hardboard is is harder than plywood and because you will likely have to drill counter sunk holes into the base, you will want something stronger than plywood to take that force.
The hardboard I used was 8 inches wide by about 10 inches long. All you really need to make sure is that there is pleny of room for your router to sit on the board both end to end and side to side. You will also need a couple of wooden slide pieces that will sit underneath the jig that will ride along the wood you are going to be making the morises in. I make mine a little bit long than the base because I like to be able to quickly see where th 2 sides are sliding on each side of the wood I will be mortising ... just handier that way. The dimensions of my sliders was 13 inches by 3/4 by 2 inches high. The other thing you will need are a couple of 1/4" hanger bolts with matching wingnuts and flat washers.
You will need to start off by taking the base off your router and using it as a template for the new hardboard base you will be building. Find the center of your hardboard and use that to drill a hole that is similar in size to the hole in your router base, that way it is easier to line up. Don't worry if hole is off a bit from you router, that won't make any difference in your cuts. Next you will need to carefully match the holes in your existing router base and make new matching ones in your new hardboard base. You can of make the new holes a wee bit larger to accomodate slight differences in your measuring, and again, these should not make a difference in your final assembly as long as all the bolts go on firmly and the base is firmly attached to your router.
Next you will need to cut some slots in your new hardboard base. You cand do these a variety of ways too, like I did on a the router table, or you could use the table saw with a 7-1/4" circular saw blade installed, by firmly attaching the hardboard to the table saw's table and lower the blade, then turn on the saw and slowly raise it up through the hardboard base. This will give you nice clean edges, but you will need to finish these off with a hand saw, and of course there are many other ways of making these slots.
Next comes inserting the hanger bolts into the 2 sliders, Attach one end first, theny use it to carefully figure out where the 2 hanger bolds will need to be screwed into. It's best to pre-drill the holes for the hanger bolts. When you try to attach the 2 slider pieces, if they bind it could be because the slot is to narrow on one side or the other. The sliders should move quite freely on the hardboard base so widening the slots may be need. Sandpaper or an appropriate file will work fine for this but do a bit at a time and test the fit, you don't want these slots too wide.
Once you have inserted the hanger bolts and made any adjustments, the mortise jig is ready to use. Attach the 2 slider pieces and bolt the base of the jig to your rotuer.
In order to make mortises, there are many variables. Some people prefer to make the tenons first then match the mortises to that, other prefer to make mortises first and tenons after. What ever you preference is do it as you like and don't be afraid to try methods too. I still like to mark out the mortises, at least the ends, and if possible, I like to put woodend stoppers so that I get nice crisp ends in my mortises, but again, do what your prefer.
This jig does take a little bit of time to set up and you will want to make test cuts to make sure your mortises are exactly where you want them. Offseting mortises is one way to cut them that is a bit more forgiving than trying to make mortise and tenon joints that line up perfectly on the same plane and remember that with mortise and tenon joinery, practice does make a difference.
Copyright Colin Knecht