Prototyping a percussion instrument

I had an idea a while ago. I remember seeing an instructional video in which Bill Bruford was playing a complex rolling pattern between his toms and a tongue drum placed on his snare. For clarity, a tongue drum (sometimes called a slit drum) usually looks something like this. You've seen them.

I thought it would be cool to make a circular tongue drum. I played with a number of configurations of rectangular tongues, but finally realized that the shape was calling for a radial arrangement of wedge-shaped tongues instead. Like this.

I have a lot of baltic birch plywood around from cabinet projects, and so I took a first pass at a prototype using one of those panels.

To cut the interior kerfs and allow the tongues to vibrate, I drilled through at the endpoints of the lines and threaded a scrollsaw blade through the hole.

Once the tongues were cut, I cut outside the diameter mark on the bandsaw to complete the rough top. My scrollsaw technique is very rusty, and those inside cuts aren't up to production quality. Better to make the mistakes on the prototype.

I thought I would try pulling a strip of the plywood around the radius by kerfing its backside every half inch.

To cut the regular kerf spacing quickly, I hacked a quick jig onto the tablesaw mitre gauge.

That's a fat roofing nail, nearly a full kerf thick, with its head cut off. Each cut kerf fits over the nail to position the next pass. Very quick, very accurate.

I used the waste from the top as a clamping form to glue the side closed in a rough circle. I had counted on the material curving evenly, but of course it did no such thing.

To try to bring it into round, I cut some spacers and arranged them inside. It helped, but not enough.

I glued the top to the side while it was still clamped to the form.

Finishing Bikes and Trees 3

This is the workpiece in progress, and in pieces.

And this is a closeup of the problematic foot. The deep scoring is from the chuck jaws, which I had previously clamped down on the base in frustration. The bowl had held securely, yes. But.

I considered some options. I could try to turn a jam chuck, remount between centres, and carefully turn the base again. That would give me a good chance at a concentric and nicely flowing base, but given the missing half rim and likelihood of further splitting, the risk seemed too great.

I thought about evening out the distribution of the chuck marks around the diameter and making decorative features out of them, but really, all I wanted to see was the profile.

In the end, I hand-shaped the base with chisels and abrasives. The process was tedious, and the result is not concentric or even perfectly circular, but most of the charm of the profile was preserved.

Instead, I added a pedestal of bike parts. First, I disassembled a very rusty rear wheel from a ladies' cruiser with a coaster brake. I tried the hub as an extension of the profile, but it was too narrow much too soon. I wanted to see the profile flare out again.

So I cut three sections of the rim and affixed them around the hub, one end tucked under the flange and against the hub body, and the other splayed out as a foot. To get an idea of the look, I held them in place with elastic bands.

It looked good, but with three legs the profile depended on the orientation of the pedestal. I didn't like how it looked that way, and so I cut a fourth leg.

I also used the grinder to cut a recess so that the tops of the legs were outside the flange rim instead of inset. The profile of the bowl flowed into the pedestal better that way.

All welded up, I was very pleased with it. I added an 18-tooth freewheel sprocket at the top of the pedestal, which was just the right size to provide a nice finish for the pedestal top and overhang for shadows.

I cleaned the pedestal with a toothbrush and alcohol, then hand sanded the bowl to 400 grit and rubbed in a beeswax finish. I avoided oil because I didn't want to further yellow the sapwood or dull the vivid reds and oranges of the branch endgrain.

I love the contrast between the discoloured, rusty, and worn metal, the soft creamy yellow sapwood, and the explosion of reds and oranges. Sometimes persistence pays off.

Persistence in the face of turning disasters

I resolved to finally finish my nemesis bowl, whether it liked it or not, and so I firmly grabbed it by the base. I planned to figure out a way to deal with the chuck marks later.

After truing the rim AGAIN, I took my time and peeled away the central column with facing cuts from the bowl gouge. It had been my attempt to take a shortcut by cutting through the column near its base that had caused my massive catch last time, so I just grit my teeth and did it the slow way.

A chunk of loose end grain came flying off while I trued the rim, and it left an interesting shape. As I hollowed, I lost another piece.

In this photo you can see how I tried to fair the trued rim back into the out-of-true bowl body. It came quite smooth with a little sanding. And you can also see that another chunk came tearing away. I do love my helmet.

That's about half the rim gone. I won't be reversing this to finish the foot! Turning half a bowl is interesting, as you can see right through the side of the bowl as it rotates. It's a new perspective on the tool.

I finished the hollowing and smoothing of the bottom of the bowl with a round scraper, and then resorted to hand sanding to remove the substantial waviness left in the remaining wood. I also used the 120 grit cloth abrasive as a shaping tool to refine the jagged edge left by the breaks.

Very interesting, and well balanced by accident. There's more hand sanding to do, but I want to solve the problem of the broken foot next.

Throwing bowls across the shop

I had daydreamed about turning bowls from chunks of tree for years before I finally bought a lathe. I made myself learn the basics, of course. But the first time I caught a city maintenance crew felling a big tree in my neighbourhood, I scored a six-foot log. It was a dead or dying Manitoba maple with characteristic streaks of pink and red through the heartwood.

I chainsawed and split it into half rounds and set them aside to dry, but couldn't wait to turn some. I chose an odd crotch piece, wedge-shaped and massive. Any sane turner would have called it firewood, but I didn't know better and thought it would make a fine first green blank.

Look how nice and new that lathe is!

The chalk marks are where the wood was binding on the lathe bed. I just kept whacking chunks off until it would turn. When the blank was finally free, I switched on the lathe and immediately switched it off, as it was doing its best to walk across the shop from the eccentric weight distribution. (Ever wonder what's in a vibrator? A motor and an eccentric mass, not quite as shown.)

Apparently I got it roughed down somehow, and the blank sat on my shelf for seven years. I had already sawed out a wedge of splintered splits, and you can see the wax on the branch end grain.

I had tried finish turning it once already, and had more or less trued it up and begun flattening the rim when I had a catch that sent the bowl flying off the screw chuck and across the workshop. Enough time had passed that I was ready to try again.

I grabbed it by the foot, used the tailstock to adjust it to run as true as I could, and then turned a tenon for the chuck into the central column I had left while rough hollowing.

Reversed and grabbed by the tenon, I could true the figure on the new centre. After some sanding it started to look pretty good.

Time to cut a new foot. My chuck manual says that the minimum recess diameter for an inside grip is 2 3/8 inches, so I dutifully used that dimension. I was justifiably worried about the skimpiness of the foot, but foolishly ignored my misgivings.

In truth, it looks like the chuck will grab a much smaller inside diameter, maybe as little as 2 inches, and I will ignore the manual and use the smallest recess that works in future. But in this case, I went for it, had a catch in the hollowing, and sent the bowl flying across the shop again, with a chunk of the foot missing. My fault, of course. I set it aside until I am not angry with it again.

Finishing Bikes and Trees 2

With the turning complete, I had to figure out how to get a clean, straight slice through the work on the bandsaw. First, I made a sacrificial V-sled the hard way by grabbing a nasty old cedar table leg out of the burn pile, jointing and squaring it, and then taking angled cuts out on the tablesaw. Completed, it cradled the turning securely and let me use the mitre gauge to set the cut angle.

I also took the time to carefully reset the blade tension and guides so that the blade stayed quite straight and did not wander. I was rewarded with a very clean cut. I can't see any blade tracks in the photo, and it sanded dead flat in just a few strokes. (To keep flats while sanding, I lay a full sheet of sandpaper on a flat table, lay the flat of the work on it, figure out how to hold the work to avoid any rocking, and then take straight light strokes back and forth. It usually works out very well.)

A quick test fit kept me excited about the project. I like this:

But the sphere was now clearly oval, as the kerf of the cut was much thinner than the sprocket. I measured the difference with calipers and marked the excess with a round marking gauge.

Doesn't that look precise and sophisticated? I think the Fine Woodworking magazine next step would be to construct a shooting jig for a low-angle bench plane and take sweet shavings of end grain off until the marked line was just kissed. But I'm not that good.

Instead, I clamped a belt sander upside down on the bench and did my best to sand down to the line more or less flat. More less, in fact, which led to a lot more hand-sanding to restore the flat. (So maybe the shooting jig is the right thing, really.) But it got there.

I carefully put the sprocket right where I wanted it, and then traced the inside onto the wood. I had started out with the idea of a loose tenon, and then dowels, but drilling into the top was looking like trouble. I decided to use brads as pins, which let me progressively refine the orientation of the gear by adding brads.

Once the sprocket was locked in place, I snipped the heads off the brads and carefully positioned the top. Once I was certain it was where it needed to be, I pressed down to mark the pin locations, and then drilled at the marks. With a tiny drill bit, I could just hold the top to prevent it tipping on its round.

The press fit was very firm, and so I completed the assembly without glue after finally hand-sanding the turning with the grain. With a rubbed coat of walnut oil, it turned out very nearly as I had hoped:

I don't think that this will be the last of this sort of thing, as my head is exploding with variations on this theme. It's fun to be inspired!

Turning Bikes and Trees 2

Two of my lifetime passions are cycling and woodworking, bicycles and wood. I am inspired to look for interesting ways to integrate them. Here, for example, is a slightly rusty freewheel sprocket and a nice quarter section of black walnut.

My intention was to turn a sphere and bisect it with the sprocket.

The first thing to do is rough the wood down. I marked and punched the centreline I wanted at each end of the log, then bandsawed away a big chunk of waste and mounted the blank on the lathe. That's the roughing gouge sitting on the wood. It chips and peels the wood away very quickly, and doesn't rely on the work already running true for a good cut. You can just pass back and forth, sending chips flying. Eventually you will have a cylinder.

I wanted to start with a diameter similar to the gulleys of the sprocket's teeth, so I set a pair of calipers to that dimension. The parting tool is lying across the calipers, as I planned to use it to establish the diameter.

I laid out the sphere with three pencil rings, intending to leave the centre one and turn down to the outside marks. Partway there, I noticed a large split developing at the tailstock end. I stopped, flooded the crack with cyanoacrylate glue, and tightened a hose clamp around the end. (I removed the hose clamp before resuming turning! It's just posed on the lathe like this.)

I had time to think, and decided that I had better make myself a half-circle template if I was to have any hope of achieving a sphere. As it turns out, the diameter I'm eventually looking for is about 2.5 inches, and I have a hole saw in that size. I made a quick plywood template and used an orange pencil crayon to mark the highest spots.

Mark, turn away marks, mark, turn away marks... it didn't take long to get quite close to spherical. By this time my vision had changed and I wanted to leave the sphere on a simple footed post, and then set the sprocket at an angle.

I had used a square scraper to peel down the post, and now switched to using it instead of the gouge on the sphere as I crept up on the shape.

I sanded to 240 grit on the lathe and then parted the base off. I made a hash of the parting off, and the bottom of the base was indeed undercut but also badly scored. I mounted a sanding disc in a Jacob's chuck and cleaned up the base, doing penance for my turning error.

Now I had to figure out how to slice through the sphere in a straight line at the right angle. I didn't want to use the tablesaw, because I don't have a thin-kerf blade and don't want the sphere to become squashed. So I decided that meant a jig on the bandsaw and sanding to fit.