Uketopus

I've been busy recently but it's time to revisit the uketopus design. Here's what I'm envisioning.

Ukuleles

I've decided to try making some  fun and fanciful tenor ukuleles. This was sparked in part by the discovery of some really nice curly birch 1/16" veneer.  That seemed just a little skimpy for the back thickness, so I laminated it with a standard veneer. I figured this would add some stability and it increases the thickness to about .087" (2.2mm).  It worked well.

I've simplified my side bending procedure to the basics. No veneer press screws, steel slats, or attempting to register the material from the waist curve. Making a solid plywood form like this doesn't take that much time and it's made bending quick and accurate.  I've come up with a new way to construct the waist clamping caul. Rather than laboriously fitting a solid block I've used two thicknesses of  1/6" veneer screwed to the center of the crosspiece. These slide past each other and are flexible enough to bend right down into the curve. The side material is flatsawn and curly, and there was a tendency towards cross-grain splitting in my practice piece . I've used low-tack painter's tape to provide constant support on the outside curves. It worked like a charm.

A quick outside mold screwed together from scrap plywood.

Sparing the rod...

Here's a compelling case that reinforces my reasons for not using a truss rod that adjusts through the soundhole on my own guitars. This is a Washburn Festival Series acoustic/electric/ hybrid.  It's not a high-end instrument but it's in excellent shape and it does what the owner wants it to do.  Unfortunately an attempt has been made to correct a rising action by tweaking the rod.  This guitar has a double-action rod.  It seems to have been twisted the wrong way. The action was cranked up close to a full 1/4" before the nut snapped!

The only way to correct this is to remove the fingerboard and install a new rod. It might need a neck re-set  but that's impossible to evaluate in its present condition. I tend to think not. The board is bound in black plastic that might turn to goo when I apply heat. The fretboard is thin. I'll bet the frets are glued in, too.
The repair cost would come perilously close to the retail value of the instrument.  Now. If the rod had been installed the other way - adjustable at the head, then there's a good chance I could have drilled it, hooked it with some pliers and pulled it out. At the very least I would have been able to release some of the tension hopefully making it playable.
Preserving strength around the headstock is a thoughtful design feature, but in this case it has made repair economically unfeasible.

Morin Khuur Part 7

 

 I decided to experiment with producing are really antiqued finish. By adding successive layers of oil varnish tinted with artist's pigment I built up the surface and topped it off with a couple of coats of shellac-based spirit varnish (fortified with a small amount of sandarac resin). 

I polished this surface using Micromesh sanding discs backed with a felt block. This was done dry, with the intent to abrade through the layers in certain areas to replicate wear.  I used several coats of a microcrystaline wax compound, both tinted dark and left natural. This highlighted little dings and scratches on the edges and really gave the appearance of age.



I was pleased with the results.  There are no photos of the process of installing the soundpost. (A challenging operation given that there were back braces to work around - not something found in violins!) With the fittings and strings installed it looks like a real antique. I need to get a bow and try it out.  Pizzicato produces a quiet buzzy tone. I'm anxious to hear it in full voice.  I wasn't satisfied with the original pearwood pegs, (the string holes seem gigantic and I was worried about their longevity!) I turned new ones using rosewood for the shafts. I'll also have to make a case, as they aren't a stock item.



The Morin Khuur Part Six

The purfling channels are cut by hand using a simple marking gauge and the waste is removed with a tiny chisel. Rather than standard violin style purfling I decided to fill the channel with black veneer for a bold outline.

I sealed the wood using a thin coat of shellac as a barrier. Here, I'm working on building up the yellow colored "ground".  The classic Cremonese instruments usually have this base which increases the optical depth of the finish and gives a dramatic golden effect.  Using artist's  pigments in cadmium yellow and ochre, I mixed a glaze using oil-based wiping varnish as the medium. There's very little pigment - just enough to tint while preserving transparency. A couple of thin coats wiped on with a rag gives the effect I'm looking for.

The back and front, ground in place and ready for body coats of reddish-brown varnish.

Morin Khuur Part 5

In recent days I've been making some fittings. Carving the bridge was straightforward. It's quartersawn maple and resembles a violin bridge, though slightly squat and flattened to accommodate two strings in the same plane. I've never carved a violin bridge before. They're typically purchased from a supplier and only need a little work to custom-fit them to a particular instrument.

 I suppose a pair of guitar bass-tuners might be a modern update, but I think the protruding ears of the traditional peg complete the aesthetic of the head nicely. These have been roughed out in pear and still require some work to bring them to completion. Here's a view of the back of the head.

Strings are an issue. The morin khuur is traditionally strung in horse hair. This can causes issues with tuning stability, as they're hygroscopic and continually changing in dimension. Also, they wear quickly and it's difficult finding suppliers. A repair shop that repairs cello and bass bows frequently might have it hanging around in the required 36" (900mm) lengths, but I decided to use nylon monofilament to make a pair of strings. This is 0.20mm (.008") 4lb test fishing line.  I set up a couple of dowel standards the required distance apart and wrapped it around, trying my best to keep the tension even.  A total of 70 strands was used for the treble string, 100 for the bass. (So, 35 and 50 turns respectively).  Some sources suggest tying or braiding the ends in attempt to make stringing a little easier. I've opted to make an overwrapping of about 1/2" (12mm) on each end, and secure it with a little cyanoacrylate glue. It worked like a charm. The extra looped material on the end was snipped off and the finished string has a neat, threadable appearance.

The tailpiece is another lovely piece of pear. This will be hinged to the bottom block rather than using tail gut, to simplify restringing. It's bored for the strings and there's a recess chiseled into the underside to accommodate the knots which will hold them in place.

The Morin Khuur Part 4.

I've never pretended to be a master carver!  Most of the historical fiddles I researched had fairly rustic looking heads. This has aspects of horses, dogs, and dragons depending on how the light strikes it.  I'll finish cleaning it up some more prior to applying finish. The aperture for installing strings is reversed from that on violin-family instruments. They're accessable through the back of the head.

I forgot to take a picture of the head-to-neck joinery so I made a little drawing. I cut a landing on the back side of the neck, parallel to the fingerboard, 3/4" long, and a matching mortise in the head. It was a decent fit. (I had fun pushing a chisel through that hard maple).  A couple of pegs secure the joint from either side.

The Morin Khuur, Part 3

The neck will sit inside a pocket chiseled through the side material. I figured it would disguise any wood movement and add just that little extra lateral stability. The neck is set back at a 2 degree angle. The strings on the Morin Khuur are quite high, about 3/4" above the surface of the neck at the junction with the body.

The inserts are set a little deeper than the surface of the neck to allow for some material removal if at some point it becomes necessary to change the angle. I don't see this as an eventuality, but I like to make repairs as easy as possible.  Having done some tests with these inserts, I have every confidence in their ability to hold, even in end-grain.  I did a test once where I suspended a cord through an eye-bolt (in mahogany) and stepped on it like a rope-ladder.  I'm the biggest guy I know, and it held just fine.

The back is braced with two longitudinal braces and a little cross-grain seam reinforcement.  This maple made it into the scrap pile due to a nasty little knot that ran perfectly tangentially across the surface.  It's stable, but I decided to add a patch over it just in case. The back thickness runs about 3.2 mm.

All closed up.  It took some planning to come up with the correct sequence of assembly. I'm not sure this is the easiest progression, (I expect it will be fun grafting the head on to that neck with the body in tow). Still, it has come together nicely and I'm quite pleased with it.

The Morin Khuur Part 2



Here's the assembled rim structure.  For reference sake, it's about 12" (300mm) long, and almost as wide. I fashioned the end blocks from Douglas fir and you can see I've drilled them out to reduce weight. It may be difficult to see, but they are also curved slightly to reduce the possibility of standing waves in the finished box. (Caused when sound bounces repeatedly between two parallel surfaces.)
I rarely use my adjustable spherical workboard for guitars, but this seemed a good opportunity to put it to use. It's made from plywood and 1/4" hardboard tensioned with a machine screw. By cranking down the screw the radius is increased.  I went ahead and pushed it to the limit - it's capable of a 10' radius, which would be extreme on a guitar.  I'm thinking of this Morin Khuur as more of a flat-topped viola.
After scribing the contour of the form on the ribs, I went planed it down to an approximate fit.

The fit is perfected by sanding. I marked the surface to be refined with some graphite and spent about ten minutes a side working it down until the joining surfaces were smooth and clean.

Later in the day I glued the bass-bar into position using Go-bars and the spherical form as a caul. The violin makers are laughing and pointing.  No. The photo isn't reversed. The stringing on this instrument is actually opposite to that of a violin with the top string on the left hand side when looking at it from the front. Hence the bass bar is on the "wrong" side.  Seriously. I'm not joking. It's not a mistake!

Using spool clamps seemed the way to go.  Given that this is a flattop, I decided to splay the bar out to cross more grain and resist the downward tension. There will be a soundpost installed as well. The top thickness is 3mm (.0120") 

I decided to attach the neck using machine bolts and inserts and I've predrilled for those holes.





An Eastern Expedition. The Morin Khuur, Part 1

Some time ago I was contacted by a music student who casually asked if I could build an Igil or a Morin Khuur.  It took a second to pull the information out of the dark recesses of my brain's instrument archive.  I knew they were Chinese or Mongolian.  "I don't see why not.", was my reply.

The idea took root. These instruments are associated with the Tuvan culture. Tuvan music is characterized by peculiar modal octave harmonies. You may be familiar with the Mongolian throat-singing tradition  I decided on the Morin Khuur, which loosely translates to "Horse-head fiddle".  It has two strings and is bowed something like a viol, being held between the knees . What's really interesting is that the strings aren't stopped on the surface of the board, but "pinched" against the side of the fingernail or fingertip.  The sound produced is a shimmering raspy tone. It's evocative of wind and wide open spaces.

I've finished the rough work and will undertake assembly this week. As it happens, I managed to find all the materials necessary in my cast-off pile. There's a good stiff Sitka top, bigleaf maple for the sides and back, (rejected as guitar sides due to a knot), some rock maple for the neck and pegbox, and a slice of rosewood for the fingerboard. So far the only thing I've had to purchase was a piece of steel to reinforce the neck. It feels good "salvaging" these woods.

I'll document the assembly in coming days.

Sears Benchtop Jointer Review

Here's a little product review for my new acquisition. I was looking around for a jointer to help make some of my small-batch production schemes easier on the elbows. Hand planing gets tiresome if you're doing eight of the same thing.

Space is always an issue. My shop is as small as some walk-in closets. Machinery has to be compact and portable. This limits me sometimes to "home handyman" items. That being said, I look for good value.

This little jointer is from Sears in the USA. It isn't available in Canadian retail locations, but ordering online was easy - Sears is using an online customs broker which means I don't get hit for duty fees at the time of delivery. That's a nice touch. It arrived within a week.

This model (351.217890) has a 4-1/8" capacity. Small? Yes. But that's wide enough for my purposes. The main feature that drew me to this machine was the lapped granite bed and fence. The major failing with all these little benchtop machines is warped castings. The customer feedback on this one was five stars. I felt safe taking the plunge.

Assembly was quick - just screwing some brackets in place and affixing the fence. The fence pivots to 45 degrees, a feature I'm not likely to use so I screwed things down firmly at right angles. What do you know! - It was both square and flat. The depth adjustment had me scratching me head until I discovered the locking knob on the back side of the machine.

In this price range, there's no hoping for a fence that slides across the bed. If I was edge-jointing 3/4" stock continuously I might devise a plywood arrangement to slip over the fence and move the cut forward to prevent all the wear happening in the same location on the blades.

I took it for a maiden voyage using some Douglas fir scrap. The universal motor whines in the usual fashion but at least the cutter head is belt driven.

There seems to be an onboard impeller that sends the shavings flying . I'll need to buy an adapter to perfect the fit between my shop vac and the dust port.

The lines on the face of the board are from rough planing. The joined edge came out dead straight over 15". I was pleased.


Time for something more challenging. Here's a neck blank about 3-1/2" (88mm) wide. It's Honduran mahogany with some ribbon figure and a twist in the grain.

Two quick passes - I'd set the depth of cut for a shallow bite, using the supplied push blocks for safety....

And voila! Shimmering clean. There are a couple of little burnish marks from where I'd neglected to wipe the shipping oil off the edge of the machine. The 29" board came out nice and flat.

And now the ultimate test. A rough-sawn ebony fingerboard. It too posed no problem. I rushed the feed a little when doing the edge, magnifying the problem inherent in all rotary jointers. That wave can make for less-than optimal glue joints which is why I'll always clean up a joined edge on my shooting board to ensure perfectly smooth glue-friendly surfaces. It's nice to have the machine to do the bulk of the rough work though!

All in all, my first impressions are very favorable. I can't speak for durability, but out of the box this is a tool capable of fine accuracy.

Diagram of action from previous post (because sometimes blogger just don't treat me right)

Getting some Action.

I recently had the opportunity to inspect and play the early efforts of an enthusiastic new luthier. Our conversation went something like this:
(him) "I'll never use maple again, it sounds awful! There's hardly any sound."
(me) "Are you sure it's the maple?"
(him) "It has to be. The first one I made I used rosewood. It's twice as loud."
(me -resisting the urge to point out that a jackhammer is loud too...) "Let me have a look at it. "

Upon inspection I could see where things had gone off the rails. The finish work was good, as was the action. The bridge however, was very low - only about 1/4" (6mm) high. This, coupled with the beginners propensity to leave things a bit thick (just in case!) had produced an instrument with the resonant properties of a solid-body electric guitar sans amplifier.

We talked about it for a while. He had the makings of a half-decent flamenco instrument, if he wanted to strip the top and scrape the periphery down to make it more responsive. Or, if he was set on a classical sound, the other option involved loosening the bindings around neck end of the back and trying to pry it free from the heel block. With some clamping pressure and a little luck, he might be able to deform the box enough to tip the heel back a degree or two. He said he'd give it some thought.

I think the most vexing thing about the situation was that he'd done nothing wrong. He'd been very conscious about following all the instructions in the manual. Unfortunately, most of the literature available to beginners just doesn't address this issue. "Standard" dimensions are given, and things just sort of come together. Unless they don't. Most of them expect the maker to go ahead and fashion the standard bridge without measuring the geometry of their instrument as it exists. I wonder how many bridges have been discarded when it was found that they produced unplayable guitars?

What are the two factors that should most interest a guitar player? Sound and playability. (In reality cosmetics play a key role, probably more than any of us might like to imagine).

Think about this: the difference between a "flamenco" instrument and a "classical" one is a matter of two millimeters. That's the difference in height of the strings above the soundboard. Classical guitars usually have a height of between ten and 12 millimeters, flamenco guitars - more like 7-9mm. These measurements include the height of the protruding bridge bone.
Interestingly, 2mm is also the difference between "good" action, and unplayable. These measurements are directly tied to one another. Two little millimeters between success and failure.

I have a large collection of reference books. I think it's safe to say that if there's an English-language guitar construction manual I have owned it or have read it. What's amazing is that most describe the design process for the beginner in terms of the face-view of the guitar. They give average measurements for string spacing, scale length, fingerboard and body lengths. None describe a method for predicting the action of an instrument.

If I were teaching a class in construction, I think I would have students begin by drawing a simple plan view of the geometry of the bridge, action, and string lengths. Will there be a dome or arch in the top? How high? Will the fingerboard remain a constant thickness from nut to sound hole? Will the neck be pitched forward or in plane with the soundboard? What are the requirements in terms of action and string height? And what will happen if I change the thickness of my fretboard from 6mm to 5? This is the dynamic geometry that underlies the instrument. In many ways it's more important than bracing schemes or top material.

Here's a sample drawing detailing the differences between my classical and flamenco set-ups:

The tolerances are pretty close. If things are glued up and something did go wrong, it's important to realize that there's only about a millimeter of adjustment in action available to us in the saddle bone. If we're savvy, we can gain an extra half-millimeter by planing the fretboard in one direction or another. Reducing it in thickness by one millimeter at the nut end, for instance, will raise the convergence point with the saddle by a millimeter - the twelfth fret becomes the theoretical pivot point.

What's nice about the Spanish method of construction, using a workboard and having the guitar neck in place, is that this tricky geometry can be locked in and clamped down. Assuming things are kept square and measurements are accurate, there shouldn't be more than .5mm deviation in any direction, well within the adjustment tolerances of the standard set-up.

Hmmm.

My sincere apologies for not having updated my workshop blog in so long! I've had a number of unrelated projects (and rather mundane tasks) on the go in recent weeks. I am definitely still alive and kicking! My luthiery activities are scheduled around the care of a parent with Alzheimer's, and that can be a bit of a challenge.

But, that said, I look forward to writing more frequently. And thanks to all who've been so supportive. :)