3 Leg Stools – Drilling Mishaps

Recently I’ve been working on a special order set of 3 leg stools in maple. The height is a custom height, which was pretty easy to accomodate with a few minor changes to the layout and positioning of various parts, and while I was making those changes I thought it’d be a good opportunity to test out some alternative methods for drilling the leg mortises in the seat.

A few months back I saw a video posted by another furniture maker here in Japan where they were drilling holes in the seats of their own brand of stools, and they was using a really interesting two-step bit like this:

The smaller diamter drill cuts the mortise for the leg tenon, and the wide cutter cuts a seat at the same diameter as the leg. In other words the larger diameter cutter creates a housing for the leg to fully inset into the seat. In theory this style of joinery is a lot simpler than cutting an angled shoulder which butts up to the underside of the seat… which is what I’ve been doing up to this point. It seemed like it would be an interesting alternative approach so I decided to give it a try for this special run of stools.

Zooming out a bit with my camera you can see my drilling setup with the two-step drill, and a basic adjustable angle jig for drilling the leg mortises in the stool seats.

In preparation for using the new drill I modified my angle jig to accept wood inserts which can be easily replaced. I’ve drilled enough through-holes/mortises in the past to know that repeated drilling gradually wears out the material directly below the line of cut, leading to tearout issues, so having the ability to quickly remove and replace an insert for supporting the wood seemed like an easy solution. I should also mention that in the past I had been drilling the seat holes from the top side, in which case any tearout on the bottom of the cut wasn’t such an issue because it was always hidden by the leg shoulders.

After drilling out the seats this was the outcome on the bottom side. The housings for the legs came out clean around the edges but there was a bit of material to clean up on the bottom of each housing. But for the most part things looked pretty good from this side.

The exit side of the cut was a different story though.

I got a few clean through holes like this one:

But in other cases the tear out was really bad. This is the top side of the seat which will be visible.

I should have stopped as soon as I saw the first hole tear out, but I was in one of those work grooves where you’ve got everything setup and you just feel compelled to keep forging ahead. I tried a bunch of things to try and alleviate the tearout but nothing I did worked. I tried swapping out the replaceable inserts in the angle jig after drilling every hole (which seemed excessive and uneccessary) but that didn’t work. I also tried sharpening the the main cutting tooth on the drill bit to see if I could get a clean exit hole, but that also didn’t lead to much improvement.

In the end I drilled all the holes with varying degrees of tearout, which was disheartening. Wishful thinking is bad news folks. If something isn’t going right, it’s probably not going to magically change for the better. Yet somehow wishful thinking is a danger that is easy to fall into when you’re in the midst of a job and feel compelled to keep moving forward (at least I hope I’m not alone in that regard).

Anyways, after coming back to reality and realizing I had to solve the tearout problem, I did a bit of searching to find a better drilling solution. What I came up with were cemented carbide drills from a woodworking shop here in Japan. They promised these drills were super sharp and capable of drilling clean through-holes with no tearout. Pictures on the shop’s website looked promising so I ordered up a few of the drills to try out.

Here’s one of the cemented carbide drills with a couple of test cuts in a scrap piece of maple. The bits are really similar to Forstner bits with a pair of scoring teeth out the outer edges and a couple of wide teeth to hog out the waste.

The initial test holes were promising. This is the top side of the cut but the exit side also looked really clean, so I decided to give these drills a go on the stool seats.

My plan was to clean up the torn out mortises by boring them out at a larger diamter using the new cemented carbide drill, and I started by using another drill at the diameter of the existing mortises to align and position the seats back on the drilling jig.

With the seat positioned and clamped to the jig, I could swap out drills and start boring out the mortise. Here I’m starting the cut and checking that the alignment of the new hole looks good relative to the old:

And…. Success! This is the top side/show face of the mortise, crisp and clean! Definitely a satisfying moment.

And for comparison here’s one of the bad mortises prior to redrilling. It looks terrible. The brown goopyness is hide glue that I applied the day before, thinking it might soak a bit into the end grain and hold any loose chucks of wood together, and hopefully prevent any further tearout. I’m not sure if the glue did much but it seemed like a reasonable safety measure at the time.

Here’s another view of a clean redrilled mortise on the upper left and two torn out mortises.

Redrilling the mortises was a bit tedious but the end results with clean mortises on all the seats was well worth it. I’m definitely going to be using these bits from here on out.

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Drilling issues aside, I also tried out a new approach to shaping and smoothing the edges of the seats on the lathe. The lathe has always seemed like an obvious choice for this part of the job, but the size of the stool seats at 330mm is just a bit too large to fit on the inboard size of the lathe which would allow me to sandwhich the seat between the tail and headstock. The outboard side of the lathe has clearance for larger diameter work but there’s no ability to use the tailstock. Not wanting to cut any kind of hole, recess, or tenon for using a chuck, and unable to come up with another solution for holding the seats securely, I had previously shaped the seat a router and template. But recently it hit me that I could clamp the seats to some kind of wood faceplate using blocking and screws passing through the leg mortises.

The faceplate is just a scrap piece of ply screwed to the lathe’s stock faceplate. All in all this was a pretty secure and solid solution, and definitely a bit more streamlined than using the router with multiple bit changes, templates, etc.

So despite some troubles with drilling, these stools have started to come together. I’m relieved to have be able to fix the torn out mortises relatively easily. There’s still a bit more work left, but at this point the seats and legs have all been shaped and hand planed.

Maple is a fantastic wood to plane; the grain really shines and develops a ton of depth and richness.

That’s my story for this week. I’ll share some finished shots of the stools in a later post.

Thanks for reading.