I got my first chance to use a up-cutting spiral bit yesterday with my router and I have mixed reviews about it.
First, the situation. I needed to cut mortises in some posts. Eight mortises in all, to be exact. The mortise dimensions were 3/4″ wide by 3 7/8″ long by 1 3/8″ deep. So long and somewhat skinny. The bit I have is 1/2″ in diameter.
The router I used is a Porter Cable 691 with the plunge router base. Because of the depth of the cut, I knew I’d need at least a couple passes to finish the cut. I was hoping that was all I’d need.
The good part is that the bit cuts very easily and cleanly, especially when compared to a straight cutting bit. The plunge into the wood was not a problem and, as long as I didn’t attempt to remove too much material in a single pass, there was no bucking or chattering as I moved the bit through the wood. The bit even manages to eject some of the wood shavings, as I’d expect from an “up-cutter.”
The bad is that it’s not nearly as effective as I’d hoped at ejecting the shavings. While it didn’t pack the mortise with the shavings I was trying to remove in the first place, enough would get stuck to force me to remove the router, remove the shavings using my dust collector, and then restart. I did eventually figure out that I could cut the mortise in a spiral pattern that allowed the bit to force most of the shavings out. However, the going was tedious with that method and it would take 15 seconds or so of moving the router back and forth to get clear the mortise before I could resume cutting more material out.
Some perspective does help here. There are 3 ways to cut out a deep mortise: using a drill press and chisels, using a router, and using a dedicated mortiser. (I’m aware of the mortising attachment for the drill press; unfortunately, the spindle on my drill press is a non-standard size so it wouldn’t be an effective solution for my situation.) Using a drill press requires using a Forstner bit to remove the majority of the material and then squaring up the mortise with chisels. I’ve used this technique many times in the past- it’s a long, labor intensive and error prone approach. Especially in hard wood like maple or oak, it’s difficult to attain the nice vertical sidewalls in the mortise.
A dedicated mortiser (like so) is certainly a nice piece of machinery and would be ideal for the kind of work I was doing here. Unfortunately, I’m not in possession of one of these and I have no plans for obtaining such a machine anytime soon. No sense dwelling on what can’t be.
That leaves the router approach, and despite it’s not living up to expectations, the spiral up-cutter is definitely an improvement over the straight cutting bits. The overall result is superior to anything I could manage with the drill press and chisels. So given my range of options, I expect it will get plenty more use.