Tuesday, September 30, 2008

Inlay and Rosette Tricks

I'm always looking for a quicker and more accurate way to inlay without visible gaps. Inlaying a straight-edged design does help, but as always, the room for error is basically a couple thousandths. In other words, not much. The inlay either fills the mortise right up to the edge or it doesn't. Lots of fancy inlay is done on darker fingerboards like rosewood or ebony. Filling gaps in these woods is easy. Just overfill with epoxy and let the dark wood hide the errors. Inlay in lighter woods like walnut poses a challenge, and inlaying soundboards of soft spruce calls for a light touch and extreme accuracy. My technique isn't unique. However, I do have a little trick I use that improves my results. I always tack glue my inlay to the substrate with a tiny drop of CA glue. It won't budge while I scribe with a #11 Xacto blade. And it pops off quite easily afterwards.

I route the majority of the mortise with a 3/32" spiral bit, then sneak into the corners with a 1/32" bit. These little buggers are really fragile, but they cut very smoothly and allow me to get into tight corners. I clean up the very tip of the corner with the #11 Xacto.

And here's where my little trick comes in. I use a highly polished jeweler's burnisher to compress and spread the aris of the mortise wall. 99% of the time this takes care of any iffy spots in the fit. If a particular area is off by more, I'll use some extra pressure and try to smoosh the wood fibers a tad more.

The burnished areas are visible around the perimeter of the mortise. These will get scraped and sanded flat after the inlay is glued.

A matching caul puts pressure evenly on the inlay.

This is ivory in walnut.

For rosettes with inlaid central calligraphy, getting the pattern on the blank in the correct position can be tricky. There is no room for error when the border of the inlay is a 2mm circle surrounded by 2mm walnut. Any deviation from the pattern will be obvious.

I cut some tiny windows into the pattern to line up exactly where the pattern should lay. Once I position it exactly I tape one edge to the blank, flip it over, spray with 3m Super 77, flip it back and press it down. The tape acts like a hinge, returning the pattern to exact spot.

This dark walnut rosette is made from several plies of alternating grain veneer, epoxied together and cured in a press. This plywood makes for easy, predictable cutting since the "grain" of the wood is the same in every direction. And obviously it makes the rosette very strong.

After cutting the pattern, but before removing the paper.

The finished rosette. Walnut and ivory.

Saturday, September 20, 2008

Pneumatic Circle Clamp

Today some friend were visiting the shop and I had just finished clamping veneer lines onto the inner edge of the soundhole with a balloon. This technique is so simple, but it's also totally ideal for this situation. The pressure is finely adjustable, the "clamp" is extremely lightweight, the rubber is soft, it won't mar the veneer or distort the shape, the pressure is perfectly distributed around the circle, the clamp is almost free and disposable. I get a kick out of this technique every time I use it. But today I didn't get the last laugh. While my friends were in the shop I stepped out for a few minutes, but it was long enough for them to get into some mischief while I was gone. And that's what worried me. I never keep soundboards clamped in the open air like this when someone else is in the shop (or even when I'm in the shop, for that matter), so naturally I was thinking about the safety of the soundboard for those few moments, especially with half a dozen people milling around. So as I step back into the shop, I hear "what's happening with this balloon setup" followed by a loud pop and shreds of yellow rubber flying through the air. My heart skipped a beat, and an entire day of carefully fitting the rosette flashed in my mind. Once the raucous laughter settled down, I realized I'd been fooled, and then I started cracking up too. I'm still trying to figure out how they found another yellow balloon so fast.

Sunday, September 14, 2008

Assymetrical Oud Bowls

Finishing the construction of an oud bowl is a milestone. For me, the bowl is the most technically demanding aspect of oud construction. After my second instrument I decided that I wanted to duplicate the bowl shape of older ouds, specifically the shape most commonly used by the Nahat dyanasty of luthiers. My first two bowls were symmetrically shaped. In other words, I took half of the face profile and rotated it 180 degrees around the centerline of the face. Theoretically, this meant that each rib was exactly the same size and shape.

Like slicing a perfect orange in half, then separating the sections. All the sections would be identical.

My second oud had a symmetrical shape. The bowl profile at the apex was taken directly from the face profile.

The shape of Nahat bowls have two distinct differences over symmetrical bowls. The first is the shape of the tail end. It doesn't terminate (meet the face) at the apex of the curve, but rather continues back a bit past the apex to meet the face at a greater than 90 degree angle. This makes for a more aesthetically pleasing look, and more importantly it softens the bottom corner of the face.

This makes the oud more comfortable to hold, as the players arm curves around the bottom of the bowl.

The other difference occurs towards the neck end of the bowl, at the apex of the bowl. The bowl is made deeper in this area. This also gives the bowl a nicely curved shape, but the real effect here is the increase of the air volume of the bowl, and combined with the position of the deeper section itself (which is directly behind the main soundhole) the projection (volume) of the oud is increased. The greater air volume probably affects the openess and fullness of the sound as well.

There have been a lot comparisons between the shape of the oud and the shape of the human body. The closest natural shape I've found that mimics the Nahat shape is actually a kalamata olive. Can you spot the oud in the following picture?

Departing from a symmetrical shape presents all kinds of challenges. Each rib is now a different shape, and with the curved tail end, the ribs closer to the face must twist at each end. No longer is the rib simply bent in one plane, but it is now a bent and twisted rib. In order for the ribs to join at their edges seamlessly, one must accurately accomplish three tasks. 1. Bend and twist the rib to match the profile of the bowl (while matching as closely as possible the curve of the previous rib) and land flatly on the the tail end and neck end gluing blocks. 2. Joint the curved and twisted rib to the previous rib (I shoot for a light-tight joint) without altering the way the rib lands on the mould. 3. Joint the opposite edge of the rib in preparation for the next rib. For me, this involves a stepped approach of gradually tweaking the bend and twist of a square-sectioned rib until I'm close, sawing the taper in one side, jointing the edge on an inverted jointer plane, further tweaking the bend and twist, final fitting of the edge, and finally, sawing and jointing the opposite edge.

Sometimes during this process, the taper of the rib itself will be off, causing the widest part of the rib to depart from the mould, instead of hugging the shape. More material must be removed from the ends of the rib in order to pivot the rib into correct position. Of course, this can drastically change the twist of the rib, which must then be corrected on the hot bending iron.

If the rib continues to need twisting, I'll heat the rib in the area I want to twist, place the rib on the mould, then gently but firmly twist the rib by hand while it's still pliable. Alternating jointing the edge and bending/twisting is necessary to avoid overcompensation of either tasks. I prefer to fit all ribs with oversized (by at least 1cm) square sectioned blanks in order to leave the most room for fitting. On good days, I can fit a rib in a little over an hour. On bad days, I just chuck the problematic rib across the shop and call it a day.

When things go well, I end up with a bowl of the intended shape and size, and a feeling of relief after accomplishing the most difficult part of oud construction. My latest oud bowl is taken directly from the shape of the old Nahats.

Monday, September 8, 2008

The Benchcrafted Tail Vise-Now Available

I'm excited to announce that the Benchcrafted Tail Vise is now available!

Introductory pricing is only $315 for the complete vise. All you have to provide is the wooden dog block to fit your bench.

Details can be found at the Benchcrafted Website. Click on the Ordering tab to place an order.

Vises are built on a made-to-order basis, and turnaround time should only be 2-3 weeks. Eventually the vises will be a stock item, and shipment time will only be a day or two.

As always, email with any questions.