You don't need a lot of horsepower for mortising, but your choice should have a 1/2" or 12 mm collet. If you can get the smaller collet to go with it (either 1/4" or 7 mm) that would be good to have too. I suggest getting one of the 2-2 1/2 hp multi base router sets, as it will not only be the best choice for mortising, but also most of the rest of your routing needs. Find one that is balanced well and is as light as possible to you when holding it, because you are going to want it to have a low profile and as light as possible, since you will be lifting it on and off of your mortising jig, likely many times. The plunge base is the best choice for mortising, in most cases. You could buy a 7/8 or 1 hp router, and although they are much lighter, they don't make them with the 1/2" or 12 mm collets, so you would be limited in the bit sizes that would fit in it.
I frequently do mortise and tenon work with my DeWalt DW618 multi-base router kits, but look at and check the balance and weight of any router that you like. In this 2-2 1/2 hp size there are many brands to choose from. Find one that is right for you. Compare the weight, plunge action, switch location, etc, before deciding. All of the better brands will likely last you many years, possibly your lifetime. Choose wisely, and not by price alone..
Most mortising work requires router bushings and a jig to guide the router. There are many plans available for these, but also some manufactured models. Again, choose wisely or make your own, depending on your need. Up spiral router bits capable of cutting downward as well as sideways are the best choice for mortising. Some bits are available with no bottom cutting capability, so again, choose wisely.
When router mortising, it's best to make many overlapping downward plunges to the full mortise depth, overlapping each plunge until the full width of the mortise has been reached. Then go back and remove the remaining waste using side to side motion at full mortise depth to clean out the remaining waste. A movement with the router bushing against both the front and back of the guide should be part of this. This is more important when using a smaller bit than the desired mortise width, but it is a good practice to follow regardless.
Are you planning to make floating tenon joints, or make tenons some other way to fit these mortises?
Charley
