Octave mandolins (part five)

With the two curved sides attached to the neck and tail blocks, I have the basic pear shaped outline of the body. The soundboard and back will be cut to this shape and glued to the sides. Because the sides are only .10″ thick and I will be installing binding, I need to increase the gluing surface by gluing kerfed linings along the edges of the sides.

Linings are sometimes solid strips of wood that are steam bent to the inside shape of the sides. That’s difficult to do because thin strips often break or splinter. I will be making “kerfed” linings. A kerf is a saw cut and kerfed linings are thin strips of wood (in this case spruce) with perpendicular kerfs cut almost all of the way through and with a uniform spacing. Cut in this way, it’s easy to bend the linings to the curve of the sides.

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The sled has a fence on top to align the strips. The narrow slider on the bottom fits into the channel of the bandsaw table.

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A clamp positioned at the end of the channel (not shown) stops the sled before the blade cuts all the way through.

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Uniform kerfs make the strips flexible.

 

 

 

 

 

Two mandolins will require a lot of linings. I can cut them with my bandsaw and to make the job less tedious, I made a little saw sled. The kerfing sled holds two blank strips square to the saw blade and stops the cut short of going all of the way through. There are small index marks on the top of the fence so that after each cut, I slide the stacked strips over one mark (about 3/16″) to make the next cut.

 

 

 

 

DSC05512The finished linings are glued inside the top and bottom edges of the instrument’s sides. I clamp them with binder clips, some odd clamps, and most of Mrs. WHBIT’s clothes pins.

 

 

Octave mandolins (part four)

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Mahogany tail block attached to the sides and back.

After bending the OM’s sides, I glued them to the mahogany neck and tail blocks. The tail block is rather simple being 3/4″ x 2″ wide x 2-3/4″ (or the height of the sides). The wedged shaped neck block is 1-1/4″ x 2-5/8″ wide x 2-7/16″ high. It was more complicated to make because of the 3/4″ mortice for the neck joint, the countersunk hole for the neck bolt, and the 3 degree angle on the top to match the neck angle.

 

 

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A decorative insert at the tail.

Gluing the two sides to the tail block was straightforward. I aligned the squared ends of the sides to the centerline of the block and clamped them. After the glue had dried, I sawed away a wedge shape from the sides and installed a trim piece.

 

 

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Neck block glued to the sides and back.

 

 

 

 

 

 

 

Gluing the neck block was much more difficult. I clamped the sides in the mold and aligned the wedge shaped block in the apex but the glue was enough lubrication that it wanted to slide askew. Finally, with a creative clamping arrangement, everything held in place long enough for the glue to set.

 

Octave Mandolin (part three)

DSC05615Many months ago I began building my two octave mandolins by resawing genuine and African mahogany into rough sized pieces for the sides, tops, and backs. These were the first pieces that I sanded to thickness with my new Grizzly drum sander. This power sander handily milled these components to a smooth, uniform .10 inch thickness without gouging, sniping, or tearing out grain. I’m really excited to have this new tool in my shop. It will save me from a lot of tedious planing and hand sanding and greatly improve the overall quality of my future instruments.

DSC05616The OMs’ sides are 21-1/2″ long and are tapered with the tail block end being 2-3/4″ high and the heel end being 2-3/8″. This slight taper will arch the top somewhat so that the bridge will reside higher on the top than the fretboard and the heel end of the top will follow the angle of the neck.

The pear shaped body only requires a gentle curve. I bent the sides individually on a capped piece of 4″ steel pipe that I heat with a propane torch. I place a wet piece of terrycloth over the pipe which produces steam. While I gently rock the sidepieces over the steaming cloth, they gradually bend to the shape I want. I bend the two sides to the same curve but it is difficult using this method to keep them symmetrical because as they cool, they spring back a bit remembering their former shape..

DSC05513To keep the sides symmetrical while I glue them to the heel and tail blocks, I built a plywood mold using a full size half pattern that I cut from the plans. Coupled with the exact shaped outside mold is an expandable inside mold. I can align the side pieces and clamp them to hold the body shape and keep them perpendicular when I glue them to the top and back.

 

 

Octave Mandolins (part two)

Octave mandolins have been around for a long time. I have seen and played round, Florentine, and guitar shaped OMs, but most often they have been pear shaped. OM tops and backs are sometimes flat but are usually carved or bent into an arch. Floating bridges and tailpieces seem the most popular but many feature a glued, fixed, saddle/pin/bridge.

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I’m not going to reinvent the octave mandolin (not yet). Instead, I’m going to base my two instruments on the excellent plans that I purchased a couple of years ago from Don Kawalek. He has designed and developed an octave mandolin kit that he sells and conducts workshops with for small groups of students who want to make their own. A Google search of ” mandolin kits” will likely turn up a lot of folks who have built Don’s kits with great results. Some have documented the process with photos much better than I’m about to, but I intend to build from scratch. I will be milling and drilling, bending and shaping all of the components myself. In a sense I am making my own kits but if I had any sense at all I would just buy Don’s.

Besides having the materials (and hopefully) the time to build two OMs, I intend to construct them a bit different from each other to compare how they sound. Both instruments will be constructed mostly of mahogany. The main difference will be that one will have a Sitka spruce soundboard. There’s nothing remotely scientific here. So many other factors are involved in the production of tone and voice that I cannot build enough nearly identical instruments to isolate each and every one. I can only accept the end product and learn from the little things that it teaches me along the way.

 

 

 

Octave Mandolin(s) part one

As a luthier and informal musician with IAD (instrument acquisition disorder) I have built many, many different kinds of instruments partly to see if I could, but also to see if I could learn to play them. I have had limited success as evidenced by the dusty hoard hanging from the walls and stacked in the corners of my house. The instruments that I actually play most often are mountain dulcimers and banjos (nowadays mostly dulcijo) with mandolins a close third.

I love a mandolin. Over the years I have owned and built a few “A” styles. The tuning and fingering is similar to the tenor banjos I played as a lad and the fiddles I later tortured out in the barn (still not allowed in the house). Learning to play one seems to help me learn the to play the others so I hope that holds true for my new project, octave mandolins.

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Example of an octave mandolin, sometimes called an Irish Bouzouki.

Octave mandolins are basically larger mandolins with a longer scale. They are usually tuned a whole octave below a standard mandolin or fiddle and produce a deeper tone with greater sustain.

I’m building mine with eight strings in four pairs tuned G-D-A-E like a fiddle or a standard mandolin except one full octave lower. Where a standard modern mandolin usually has a 13-7/8″ scale, this lower tuned instrument will have a 22-1/2″ scale.

Almost two years ago, in anticipation of this project, I milled a batch of genuine and African mahogany. Autoharps, autoharps, autoharps have kept the project on the back burner so I recently decided, now or never. When I began collating my materials and ideas, I realized that I had enough to make two octave mandolins. I reasoned that I could build them slightly different, decide which I liked best, and sell the other. Experience reminds me that I’ll make all of the mistakes on the first one, play the second one, and keep both for the hoard.

A new autoharp

DSC05485Lately, much of my workshop time has been spent building left handed autoharps for the musicians who realize the advantages of that reverse configuration. Finally, (pun alert!) I made one right.

 

This new autoharp is built in the standard right handed configuration and will be played by its owner in the upright position, sometimes with a strap. It’s a 37 string chromatic, eighteen chord, with a Sitka spruce soundboard, walnut trim, and a dragonfly shaped rosette.

 

DSC05493There are several rather deluxe features. The back is fitted with a removable resonator and “snap lock” strap attachment.

 

DSC05489 Eighteen very thin chord bars were made by Buck Lumbert and allow for ample playing room at the high strings.

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Black oxide zither pins and Daigle Flatline fine tuners make for precise tuning adjustment.

 

 

 

 

 

 

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Showing the pickup strip between the chord bar holders before stringing.

Concealed beneath the strings and chord bars is an electromagnetic pickup that was ordered from Greg Schreiber for this 37 string instrument. The metal tabs on each end of the strip are held in channels that are milled on the undersides of the chord comb bases. Wiring passes through the soundboard to a jack that is imbedded in the curved treble side.

 

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A diatonic autoharp conversion (part six and final)

G-A-B-D-E-F#-G-A-B-C-C-C#-D-D

 E-E-F#-G-G-A-A-B-B-C-C#-D-D-E-E-F#-G-G-A-A-B-C

The 36 string, Oscar Schmidt 21-C has finally been converted from a standard chromatic to a two key diatonic in the keys of “G” and “D”. The new tuning schedule shown above lists from low to high the wound bass strings from number one, “G”, to number fourteen, “D”. The remaining twenty-two plain strings continue from number fifteen, “E”, to number thirty-six, “C”. This new tuning differs from the previous chromatic tuning in two significant ways. Notes that do not appear in the diatonic (do-re-mi-fa-sol-la-ti-do) scales of “G” and “D” will just get in the way so they aren’t invited to the party. Their absence  leaves room for some double notes in the center of the dance floor where the real party animals play. When playing melody, these note pairs are easier to strike accurately and they sound louder.

DSC05471With the change in tuning comes a change in the chord array. As the keys of “G” and “D” are adjacent in the “circle of fifths”, they share some of the same chords. These chords are arranged in a common pattern that can be played mostly the same in either key by shifting the fingers over a row or two. This autoharp has twenty-one chord bars arranged in three rows. Initially, only thirteen chords are needed along with two “lock bars”. The extra six bars remain felted but uncut until such time as other chords are desired.

 

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The plastic buttons can slide in the U-shaped chord bar to any position in the three rows.

Chord bars and buttons on these Oscars allow placing the cut chords almost anywhere in the array. The channeled bars can be swapped about on different combs and the buttons can be positioned in any of the three rows. The old buttons that are labeled with standard chords may be recycled but some labeled chord buttons aren’t included in the standard sets. For consistency, I purchased blank buttons from Elderly instruments at $1 each, and labeled them with peel-and-stick chord bar labels.

Most parties have their little cliques and our autoharp party with the “G”s dancing with the “D”s is no different. Everybody has a good time but there always seems to be those who don’t get on well with the other group. In this case you “C”s and “C#”s know who you are. Since there is no “C” note in the key of “D” scale and no “C#” note in the key of “G” they are locked out.

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The “D lock bar” button has a portion cut away.

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The “D lock bar” is engaged.

On this two key diatonic autoharp I have installed two “lock bars”. The “G” lock bar mutes the two “C#” strings and the “D” lock bar mutes the four “C” strings that are unwanted in their respective scales preventing those strings from being played accidentally. I modified old buttons for these two bars by cutting away a portion of their tops. A lock bar is engaged by pressing the button down and sliding/wedging the lower part under the plastic chord bar cover.

 

 

 

 

 

 

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Engaged, the “D lock bar” mutes four “C” strings.

A diatonic autoharp conversion (part five)

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Chord bars with the old felt.

Now I turn my attention to the original chord set by preparing it for the new diatonic tuning. The 21 extruded aluminum bars are in poor condition. The felt, besides being the wrong chords for the new tuning, is moth eaten and heavily worn. Before I can install new felt strips I must remove all of the old along with the adhesive residue.

The original felt blocks are easy to break free of the bars but the old brittle adhesive remains. The tedious task of removing it involves soaking/heating the bars in very hot water and scraping it off with my thumbnail and a chisel. I use a stinky solvent called Goof-Off and 0000 steel wool to clean up the remaining glue boogers. A soft cloth and naphtha puts a final end to the old glue and leaves the bars clean and shiny.

DSC05233The chord bars are aligned on each side of the autoharp with plastic combs. On the end of each bar is a slot and on the opposite end a hole. These apertures must slide freely up and down on their combs. The holes in most of the bars were improperly drilled leaving sharp burrs that could snag on the combs. It was easy to deburr the soft aluminum with a file.

DSC05234With all of the bars smooth and shiny, I install new premium chord bar felt. I purchase rolls of felt in bulk from Aetna Felt Company but bar sized strips can be ordered here, from other autoharp luthiers, or Elderly Instruments in Lansing MI. The felt is peel-and-stick which works good on clean bars but I like to improve adhesion by first applying a thin coat of contact adhesive to the bars and letting it dry a bit before applying the felt. When I cut the strips a little long I can trim it back with a sharp knife when I cut the chords.

A Diatonic Autoharp Conversion (part four)

While I wait for the arrival of the custom string set, I prepare the autoharp body, install new tuning pins, and re-name them.

This modern style “C” has a multi-ply pin block frame and a plywood top/back that are painted with an amber/brown sunburst. After I removed the grime with a damp cloth and a little 409 cleaner, it seemed in pretty good condition except for some scuffs on the sides. Fortunately, it didn’t require re-finishing. I lightly sanded the abrasions, re-colored them with a matching brown aniline dye/alcohol mixture, and then applied a light coat of “Tru-Oil”. Later, I polished  the painted surfaces with a paste wax being careful not to get any in the open tuning pin holes.

DSC05235The note designation of each tuning pin was painted in white just south of each hole. In its former career this autoharp was a standard chromatic tuned from a low F2 to a high C6. The new G/D diatonic tuning schedule will require new names for more than half of the pins so I re-labeled them all. For this I used gold, peel-and-stick labels that were printed for this purpose by Judy Danzer. She no longer makes them but I think they are now available from Daigle Autoharps.

DSC05239The exposed threads of the original tuning pins were corroded and most of their heads had been mutilated by bad tuning wrenches. I replace all 36 with new nickel plated pins which I carefully drive into the holes with a hammer. Newly manufactured pins seem to have a light coating of oil to help keep them shiny. Since I don’t want even a little amount of lubricant to contaminate the pin block, I clean the pin threads with naptha before driving them.

A Diatonic Autoharp Conversion (part three)

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On the original bar, the ball end strings are hooked in the slots and then stretch up across the cap of the pointed bridge.

A “C” model autoharp like this  Oscar Schmidt has a 5/8″ x  9-1/4″ x 15/16″ pocket routed into the top at the anchor end for an extruded aluminium anchor bar. The bar is a combination  bridge and the slots that hold the ball ends of the 36 strings. It merely sits in the pocket and is wedged tightly in place by the lateral string tension.

I think that the anchor bar is quite a clever design. It’s light in weight and does its job very well… except when it doesn’t.  Sometimes it can creep up and even jump free of the pocket. That’s frightening when it happens but it can usually be re-seated, blocked, and screwed to the frame inside the pocket.

 

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On a conventional installation, the Daigle fine tuners are screwed to the tail end of the autoharp. A wood knee rest will cover the base plate and screw heads.

The Daigle Flat Line Fine Tuners aren’t designed as a direct replacement for the OS anchor bar. In a conventional installation, the back plate hangs over the end of the autoharp and is firmly screwed to the frame. A flat, brass wire capped bridge rests just in front of the aluminium bar.

 

 

 

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The precision base is screwed to the head of the Dremmel router. It makes it easier to guide the cutter and can be finely adjusted to control the depth of cut

To install the Daigle tuners in the OS  I must widen the pocket so that the new bridge will be in the same position as the old. I use my Dremel router attached to a Stewart-MacDonald precision router base to widen the pocket from 5/8″ to 7/8″. First, I cut to the depth of the plywood top and then into the soft wood below as deep as the base will allow. For the last 1/4″ or so of depth, I remove the material freehand without the base.

 

 

 

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A filler block is screwed to the front of the fine tuner bar to hold the assembly to the rear of the slot. The ends are painted black to make the maple less visible beneath the chrome cover.

 

 

 

Now, when the bar is positioned all of the way to the rear of the pocket, the flat, brass wire capped bridge will be in the same line as the original bridge. To fill the empty area of the pocket in front of the new bar, I cut a 3/4″ wide piece of maple and attach it to the bar with flathead wood screws.

 

 

 

 

DSC05211The new fine tuners with the the block fit snuggly in the pocket. This assembly should  work much the same as the old OS bar but I have concerns that it could fail. Since I cannot conceal retaining screws in the pocket, I am going to shim it tight and glue it. This raises a new concern. What if it’s necessary to remove the fine tuners for replacement or repair? Gluing doesn’t seem easily reversible. I’m spectulating that if anything happens to the fine tuners, say fracture or extreme wear, they will require a new replacement. In that case, the old is no longer useful and can be cut from the frame. That would be a “worst case” but I’m confident of the quality of the Daigle tuners and don’t expect them to fail unless the instrument is abused or dropped.