Plumbers typically cut chamfered drain holes in subflooring by eye, using a recip saw held at a shallow angle. The resulting inconsistencies in the roundness of the hole and the chamfered angles can keep the drain from sitting totally flat and centered in the opening, and a generous application of construction adhesive is often required to support the drain fitting properly. Another problem is that such "subfloor surgery" can take even a skilled worker 15 minutes to do well.

The Stall Saw was designed to get this job done quickly and efficiently. The cutting tool mounts onto a 5-1/2-inch hole saw. Its three outside blades function as a giant countersink cutter, chamfering the straight sides of the hole left by the hole saw. This chamfered hole fits the 45-degree-angled bottom of common shower drains and provides a uniform, level bearing surface to seat the drain body.

Straight out of the box, the tool is a bit bewildering. The production model is different in both material and design from the prototype shown on the company's Web site, which made me wonder if different models were available. Also, it comes with no instructions other than the recommendation to watch a brief online demo video that leaves lots of unanswered questions about the tool's assembly and adjustment.

To set up the tool, you must first fit it over your 5-1/2-inch hole saw. Any brand should do, but in keeping with the manufacturer's recommendation for the fastest cutting in wood subfloors, we used a LENOX One Tooth rough wood hole cutter. This saw has one big carbide tooth and a generous gullet slot for clearing big chips. Make sure to have the correct extra-long pilot bit installed in the One Tooth hole saw before attaching the Stall Saw, because the thick plastic at the top of the Stall Saw covers the set screw used to secure the pilot bit. The three blades of the Stall Saw have to be removed to slide its reinforced plastic body down over the hole saw.

Once the Stall Saw is placed over the hole saw, you line up the three mounting bolt holes and tighten each one a little at a time in sequence to help keep the assembly centered. As for the direction of the acorn nuts, I put them to the inside of the extra-deep One Tooth saw, reasoning that their height would keep wooden plugs from getting stuck in the hole saw. For shallower hole saws, check that the nuts won't bottom out against the subfloor and halt the cutting action before the wood is cut through.

The blades are held in their slots with large sheet-metal screws threaded directly into the plastic body of the tool, and I almost stripped the Phillips head on one of the screws that was assembled too tightly. I was surprised at this design detail; it made me wonder how long the plastic would hold up to repeated tightening and loosening of the screws. I will leave this hole saw permanently mounted, and minimize the wear.

The blades are reversible (and sharpenable) for longer life, but curiously, not all blades fit in each slot. In one-third of the possible blade-fitting positions, the blades would not seat in the plastic slot far enough for the screw to line up with its hole; and in some other combinations, the screw went in at quite an angle – which could hasten the wear on the plastic threads and perhaps eventually cause the screw to snap off. I suggest marking the blades before removing them, so that they go back in the same slots. And if you are reversing the blades to expose a new cutting edge, loose-fit them in the slots and check that they all line up well before installing the screws.

I guessed at the proper setting of the depth-stop bolts (mounted just outboard of the cutters) and made sure all three were at the same height. These could be readjusted to set the depth for a specific drain fitting later, if need be.

With the assembly details figured out, I finally got to try the Stall Saw. I made Swiss cheese out of a piece of OSB subfloor, double-checking the depth-of-cut setting and getting way more experience with the tool than I'd get from the one or two custom shower installs in an average house project.

The hole saw and bevel cutters work almost effortlessly in a large right-angle drill, and the fresh blades all left very nice clean cuts.

The narrow depth-stop bolts gouge a deep groove in the subfloor, and therefore don't really stop the cutting depth. This offended my sense of craftsmanship, but I learned to use the evenness of the groove as a guide when cutting. If you don't hold the bit assembly completely flat to the floor, the angle of the bevel will be off on one side and must be fixed by more drilling. Seeing the bolts score an even groove around the hole means you are holding it properly.

I tested the Stall Saw on plywood and cut into the top of a 2-by joist underneath with very smooth results. I also planted nails where the Stall Saw would hit them for a torture test of its blades. The blades had a tendency to bounce over the nails, slightly pulling and shaving them without shearing through. I had to stop and pull the nails to keep making the cut, but such "accidental" contact didn't seem to damage the blades.

When I took the Stall Saw to one of my jobs, it worked like a dream. As I cut perfectly proportioned drain holes in mere seconds, I felt the warm satisfaction of finally having and using the right tool for the job.

Regarding the LENOX One Tooth hole saw's contribution to the rig's efficiency: This too is the right tool for the job anytime you're cutting wood with a hole saw. The 2-inch-deep saw has twice the depth-of-cut of a standard hole saw and requires a longer pilot bit. I cut off an old spade bit and fitted it to an arbor so I could use the saw without delay. In fact, with a stubby spade bit installed, the One Tooth saw can be used to cut low-angle holes through framing lumber that you couldn't achieve with a self-feeding plumber's bit. That's actually the reason for the extra depth of the One Tooth saw design.

The Verdict

The Stall Saw adapter fitted to a 5-1/2-inch LENOX One Tooth hole saw impressed us with its ability to cut accurate and uniform shower-drain holes – and to do so in record time. The price of the combined components is certainly reasonable for a specialty trade tool, but leaving a new owner to his own devices to assemble and maintain the product without a written manual is a lapse in customer service.

STALL SAW Drain-cutting tool
Price: $80 (plus $10 shipping)

LENOX 5-1/2-inch one-tooth hole saw
Price: $60

John Myrtle, owner of JM Plumbing and Heating in Hotchkiss, Colo., contributed to this article.