Tarjo Bluegrass 5 Strings .Model Z6.2

It was impossible to find a 5-string bluegrass banjo in a guitar body online.

Since I love a challenge, I bought a broken acoustic guitar for 5 euros. (The neck , the tuning keys and body were fine, but the bridge, and saddles were unusable for a guitar.)

I decided to transform this guitar into a 5-string bluegrass banjo because the neck is thin (not as wide as a classical guitar) and it has a truss rod (a reinforcement bar in the neck, essential to compensate for the tension of the metal strings).

My 5-string bluegrass Tarjo is inspired by the 6-string Tarjo already published on Instructables.com.

https://www.instructables.com/The-Tarjo-a-Nylon-strung-Guitar-Banjo-Made-From-an/

made by ZaxZaxx. Thanks to him.

Materials

1. Oak parquet boards 240x24x6mm + 48 M4x50 screws + M4 nuts + 96 D=4mm washers for the banjo body and its support
2. Plastic film for the banjo head (see text)
3. 1 M3x10 hexagonal spacer
4. Wood glue and epoxy glue
5. Fir board approximately 300x600x20mm (to reinforce the acoustic soundboard)

Tools

1. Standard hand tools, ruler, compass,
2. Table saw
3. Band saw
4. Drill + drill bits
5. 40, 80, 120 grit sandpaper
6. Time = approximately 4 days excluding glue drying

The Tarjo 5-string bluegrass guitar features the following innovations compared to the ZaxZaxx Tarjo 6-string guitar:

1. Use of metal strings (the folk guitar has a truss rod), which requires structural reinforcement.
2. Manufacture of the banjo head (with 6mm-thick parquet slats) and use of Mylar film recovered from a flat computer screen. No wood lathe required.
3. Creation of a support to rest the banjo head inside the guitar body. This assembly is glued to the bottom of the body, even though the top (acoustic top) and bottom (back) of the guitar are not parallel. Furthermore, the head support is height-adjustable so that the banjo head's skin is flush with the guitar's acoustic top.
4. Preparation of the body: Reinforcement of the inside of the sound box.
5. Reusing the guitar bridge to create a tailpiece for the banjo.
6. Custom-drilled vents.
7. Mounting the high drone string (G/G) at the 5th fret without a machine head in the middle of the neck.
8. The Tarjo 5-string bluegrass banjo (G-D G-B-T = G-D-G-B-D) can be re-strung as a Tarjo 6-string guitar (E-A-D-G-B-E = E-A-D-G-B-E).

To fit the acoustic guitar I had, the banjo head needed to have a maximum diameter of 240mm and a height of 36mm.

When I dismantled my floor at home, I kept a few undamaged oak planks (240mmx24mmx6mm). I decided to cut/assemble/glue them to form a banjo head with six layers (6mm each) of large 16-sided polygons (hexadecagons).

For a diameter of 240mm and 24mm wide planks, the calculation (online simulator) told me

that the angles of each piece of the hexadecagon should be 11.25° (because 2x11.25° x 16= 360°),

the large base of each piece should be 48mm, and the small base should be 38mm.

The diameter of the inscribed circle of the head is 192mm.

I first cut a perfect 192mm disc from a thick board.

I then cut (with a circular saw) 6x16 = 96 pieces using a template that allowed me to easily create the 11.25° angles.

Next, I glued the 96 pieces in 6 layers of 16 pieces each around the 192mm diameter disc (being careful not to glue the disc), and offset the layers relative to each other.

After pressing and drying, we obtain a polygon with lots of points on the outside, and we need to make this polygon perfectly cylindrical. I first removed most of the excess polygon with a band saw, then screwed the head's inner disc into its center on my circular saw, and then smoothed the edges by rotating the head around the disc until the outer circle was perfect.

In my case, the resulting outer circle was 236mm.

Then, using a wood file, I roughly smoothed the inner diameter (to make it look cleaner, but this step isn't essential, I think).

Next, I drilled 3x16 = 48 equally spaced through holes, each 4mm in diameter (a tricky operation: you need a perfect layout).

Next, I took a sheet of Mylar that I had recovered while disassembling (out of curiosity) a flat screen PC. It turned out to be perfect for the job. I think it's possible to use any smooth polypropylene (PET) plastic sheet from a large soda bottle, for example.

I roughly cut it and placed it on the head and made a first 4mm diameter hole with a soldering iron (fine tip). I placed a flat washer and an M4x50 hex screw. I did the same thing for the next hole, etc. In total, 48 times, so...

I turned the head over and screwed on the 48 washers and 48 nuts.

Then (still upside down) I heated the sheet with a heat gun (500°C) at a height of 30cm for a few minutes. Not too close, or it would make a hole! And I'd have to start all over again! I did it backwards because it avoids heating the screws and risking warping the sheet.

After cooling, the head should sound like a tambourine; otherwise, let's start again!

At the end of this step, I trimmed the excess Mylar from the outer diameter with a cutter.

Protect the Acoustic Top

My banjo's headstock measured 236mm in diameter. So I drilled a slightly larger hole (238mm) in the body so I could easily remove it if necessary.

To determine the center of the hole in the body, first locate and mark the center of the current nut. Normally, the distance between the 12th fret and the center of the bridge saddle is equal to the scale length (distance between the neck saddle and the 12th fret) + the compensation for steel strings (= approximately 2mm).

For better sound, the banjo's bridge is not positioned in the center of the headstock, but offset 1/3 of the diameter from the edge. This is why you see an offset of the center of the banjo headstock from the original guitar bridge. Trace and drill the acoustic top precisely. For my part, I used a small homemade handsaw and made a sanding block with the same radius as the banjo headstock using 40-grit sandpaper held in place with double-sided tape.

Keep the scrap piece that supports the bridge.

Drilling the sound holes:

Starting from the center of the banjo headstock, I traced a circle with a radius of 190mm, and arranged (to my liking) holes of varying diameters so that the sound could escape from the body.

I drilled with a multi-diameter drill bit.

Nothing special about this step. Heat the bridge with a heat gun (not too close) and slide a cutter blade between the soundboard and the bridge to loosen and lift it.

Keep the offcut, which will be used later to fill the soundhole.

Drilling a hole in the body for the banjo headstock weakened the guitar considerably. If it's not reinforced, it will bend under the tension of the strings. Furthermore, the guitar headstock must be centered and held in the correct position.

For your information, here is the plan I used for my guitar.

The brace is made in two parts (so it can be mounted in the body using a 20mm board). It's heavy, but that way I'm safe.

The acoustic soundboard must be smooth underneath before gluing the brace. Once the braces from the old guitar are removed (with a wood chisel), sand with 40 grit.

Adjust and glue the banjo brace (along the axis of the neck), centering it over the hole in the banjo headstock. Hold it in place with clamps or clamps and let it dry overnight.

The guitar bridge is reused as a tailpiece.

Once its location is determined, scrape off the paint (or varnish) so that the glue is applied to raw wood, then glue it (vinyl glue), holding it firmly with three clamps.

The idea is to create a support for the banjo head that rests on the bottom of the body.

Problems

1. The banjo head should not vibrate.
2. The construction of this banjo head support must be adjustable because the banjo head should just touch the surface.
3. The top and bottom of the body are not parallel: the alignment must be corrected. (In my case, the alignment error is 2.5°.)
4. The assembly must be removable and allow access to the truss rod (you never know...).
5. So I made a support in three parts.
6. At the top, a support that holds the head between two screws.
7. In the middle, adjustable shims.
8. At the bottom, a support with shims cut at 2.5° allow for correcting the horizontal alignment.
9. The whole thing is held together by four M3x40 screws + washers + Nylstop nuts.
10. Assembly: Use the photos for help.
11. First, you must make the two head supports and assemble/glue them. These will determine the final geometry of the support. Once they're done, you'll need to adjust them so they fit between the banjo tee screws, and so the banjo head rests perfectly on them. Glue them together to secure them. Mark the adjusted positions of the bracket and the head (personally, I made a dot on one side and a cross on the other). Next, you need to make the part that corrects the horizontality of the support using 2.5° beveled shims topped with a cradle.
12. Next, make the adjustment shims (in my case, two 6mm shims were enough).
13. Next, counter-drill the holes for the screws that hold the assembly together.

Assemble the three sub-assemblies without gluing anything. Adjust the height of the shims so that the banjo head is flush with the top of the acoustic soundboard. When everything is OK, then apply glue to the bottom of the body, assemble the three support assemblies, screw them in place, position the banjo head on the support, place a weight on a board above the banjo head, and let it dry overnight.

The 5-string Tarjo uses the neck of a 6-string guitar, but the location of the guitar's first string (low E/E) is not used, and the banjo's drone string (high G/G drone string) is located at the location of the guitar's second string (A/A).

The neck is not modified to accommodate a machine head at the 5th fret, but a device is inserted that plucks the string at the 5th fret. Note that this device is removable, and you can return to a 6-string Tarjo configuration at any time.

Drill a 3mm diameter hole tangent to the drone string. This hole will serve as a guide for the 5.5mm hole that will receive the threaded spacer. Be careful not to break through to the other side of the neck!

Counter-drill this hole to a 5.5mm diameter. Be careful not to break through to the other side of the neck!

Clean thoroughly.

Apply epoxy glue and force-insert an M3x10mm spacer. Make sure the spacer does not protrude beyond the fingerboard.

Let it harden overnight.

The next day, remove the epoxy that has overflowed and is preventing the M3 screw from going all the way in: VERY gently counterdrill (by hand) with a 2.5mm drill bit and re-tap the M3 screw if necessary.

Cut a 6mm diameter washer drilled 3mm deep into a thick, very hard plastic (I used a plastic similar to the one used for self-service trays) with a saw cut tangent to the inner hole that will guide the drone string while allowing it to slide. And there you have it! The neck is ready to be strung... but you have to make the banjo bridge first!

I recut this bridge from an old guitar that had given up the ghost. It is topped with a shim.

The shim and nut will need to be adjusted later (during the tuning phase) in height so that the string height is between 2mm and 2.5mm at the 12th fret.

The banjo in "Open G" tuning is:

G / high G (drone string)

D / low G

G / G

B / B

D / high D

I used the following gauges:

G / high G (drone string) = .011

D / low G = .032

G / G = .023

B / B = .015

D / high D = .013

Be careful with the string length (I got caught out by this): some brands are shorter than others (up to 15 or 20 cm). To get out of this situation, I used a set of Martin Bronze guitar strings (medium tension) that I had on the shelf.

You need:

between 0.2 and 0.3mm at the 3rd fret (adjust the nut accordingly)

between 2mm and 2.5mm at the 12th fret (adjust the banjo head bridge accordingly (as mentioned in step 10)

Put the drone string through the groove in the plastic washer and tighten the M3 screw. The string should not bind and should slide freely in the groove for G tuning.

Set the banjo head bridge to the scale length (the distance between the neck nut and the 12th fret) and tune to open G and... the banjo will sound out of tune. Don't panic: this is normal. You will need to add the compensation (about 2mm), and position the bridge slightly at an angle on the banjo head so that ALL the strings sound in tune. the octave, (at the 12th fret). The bridge position is adjusted by ear.

If the neck is straight and truss rod adjustment is not necessary, you can plug the soundhole hole with two small, discreet screws.

If necessary, I refer you to the online tutorials.

To cover the soundhole, I used the offcut from the hole I had drilled to accommodate the banjo head.

Do not glue the cover, otherwise access to the truss rod adjustment will be difficult.

Many thanks to Christian L... He's an excellent banjo player. He'll recognize himself.

Cripple creek

https://youtu.be/3l1sExZTE6c

Song for Lowel

https://youtu.be/OZNwAuQEbVQ

Future improvements will focus primarily on the bridge saddle (thanks, Christian!)

1. Currently, the string spacing at the saddle is 9mm. Banjo players recommend 11mm.
2. Small notches are needed on the saddle to keep the strings in place.
3. The bridge's bearing surface must be reduced, because the larger the surface area, the less clear and powerful the sound.

Et voilà!

I'm very happy with the result: the banjo is easy to play, and the sound is quite strong. It's a banjo sound with a resonator. A mix of banjo and guitar. That's great: it's exactly what we were looking for! In any case, it's a unique instrument!

All I have to do now is learn to play, because the technique of playing a 5-string banjo is really very different from that of playing a 6-string guitar.

Don't hesitate to contact me if you're interested in this adventure!

Greetings from France

Bruno