Dobro Style Pan Lid Guitar - Model Z5.2

I was given a destroyed folk guitar. As you see, the bridge was seriously brocken, and the wooden acoustic table was unglued inside the sound box just under the bridge. But the neck was straight and usable. I decided to keep the neck and the sound box, and to use a pan lid as a resonator.

1x old destroyed guitar in end of life (folk guitar in my case) for the body

1x Stainless steel pan lid (diameter = 31 cm in my case) for the resonator

1x IKEA Grünka (stainless steel) spatula for the tailpiece

2x 15x25x500mm empty aluminum (or wood) bars for the reinforcing of the body

Aluminum sheets (thickness 2mm, 1,-mm + M4 and M6 nuts+ Waschers + M4 and M6 Screws , screws + epoxy glue: see text

Tools : hand saw, hand drill, drill bits, files

Measure with a great precision the distance between the neck saddle and the 12th fret. Note this measurated value.

This mesasure is is important because the distance between the neck saddle and the 12th fret must be be EXACTLY the same as the distance between the bridge saddle and the 12th fret. If not, the guitar will not sound correctly.

Take out the old bridge

Protect the soundboard with adhesive paper

Draw a line from side to side of the sound box with the distance you measured above.

In the middle of this line, put a compass, draw the biggest circle you can and measure the diameter of this circle. In my case Dmax= 32cm. 

Substract 1,5cm to this value , because it exist a wooden reinforcement inside the soundbox you don't see. You obtain the maximum diameter Dmax of the hole you may cut in the sound table. In my case Dmax=32cm-1,5cm=30,5cm.  

Buy a stainless steel pan lid (not an aluminum one because the sound is bad) with a smaller diameter. In my case, by chance, I founded and I bought a stainless steel pan lid D=31cm and small ledge around the lid D=29cm.

Before buying, verify that the pan lid resonates correctly when you tap it with a fork. (people looked at me strangely when I was doing my tests in the store)

The diameter of hole you'll cut in the soud table must be even shorter than the diameter of the pan lid resonator you bought, because the pan lid will stay over the sound table (*) . In my case, there was a small ledge around the lid (D=29cm), so I drew a circle 29cm in diameter.

With a little diy handsaw (a little metal saw stuck between two woodensticks with expoxy glue) I saw a 29cm diameter hole. The sound table is reinforced with wooden bars. Cut them without any complex.

Once the hole is drilled, verify that the pan lid fits perfectly, without moving.

If the hole is too large, the resonator will vibrate, and if the hole is too short, the resonator will not stay in place and vibrate too. So I repeat: the resonator must fit perfectly, without moving. If not, fix this problem before the next step

(*) in the prototype Z5.1 model , I opened the back of the guitar, and I introduced the resonator under the sound table, but this assembly was very, very difficult to build... and not really better than the Z5.2 model.

The metal strings will develop an around 75kgs strenght : it means that the sound box must be absolutely reinforced otherwise, it will fold in 2 seconds when you'll tighten the strings.

I glued 2 aluminum bars (40cm long) inside the sound box with epoxy glue. You can use wooden bars or whatever you want.

In my case, the resonator went down to the level of the sound table, and ... Rrrrrrrr!!!! ..... It touched the aluminium bar... I needed to put an extra spacer.

So... measure correctly before, and measure again, otherwise you'll have to take off the bars, add the spacer, then re-glue !! (like me do)

I bought an IKEA Grünka (stainless steel) spatula (I think that any BBQ spatula should be OK ), and I drilled 6 holes (diameter 2mm , 1,1mm spaced ) with a sharp drill bit (stainless steel is difficult to drill). These holes will receive the strings later.

Then, I bent the spatula at 90°, and I drilled the handle in order to be able to screw it on the body.

On the final pictures, you can see that I reinforced the extremity of the spatula, but it vas before I designed the string holder. With the string holder, I think now it is not necessary anymore.

Finally I lined it inside with leather so as not to damage the body and eliminate any risk of vibration.

This is certainly the hardest part of this project. This part must comply with a lot of parameters.

1- the bridge must be able to be screwed on the pan lid resonator in its center,

2- the strings must be pulled down (as is the case with the old bridge) otherwise they float above the nut, which causes untimely vibrations.

3- Height string adjustment/tunig must be possible.

4- there is not a lot of room in height to do all that

By itself, this part requires one complete day of work, not including the drying time of the glue. It takes time to cut and precisely adjust the parts that make up the assembly

The easiest way is to refer to the plan

The bridge is made of 3 parts: 1- the base 2- The saddle 3- The string holder

1- The base has a female T-profile (made of an assembly of several aluminum sheets), as it supports the saddle, which is a male aluminum T-profile.

Remember that after the manufacturing process, the saddle must be able to move in the female part, in order to be put off and filed later during the adjustment process. The saddle and the intermediate aluminium sheet(part 2 and 4 on the drawing) must have the same thickness.

When I glued the different parts, I washed the female parts with alcohol, I put oil on the male saddle (so that it cannot stick in the female part), I put the saddle in the T female profile, and pressed all the parts together, and I let them to dry. Be careful! , wash conscientiously the female part, and generously oil the male saddle otherwise everything will be stuck, and the bridge is lost! (unfortunately I made the mistake)

Then Drill a diameter 6mm countersunk hole just in the center. This hole will receive the M6 countersunk screw in order to maintain the bridge and the resonator together.

Then insert in force and glue with exoxy 3xM4 nuts as described on the plan (between 2 strings).

The two extreme nuts will close the strings lid, and the third (in the middle) will help to tight the base on the resonator.

2- The saddle

It is a male aluminium T profile (thickness 1,6mm) , bought in the DIY store. No particular problem. It must fit and be able to slide in the female base

3- The string cover. (Aluminium sheet thickness 1,6mm)This part must guide the strings (11mm apart) and press them in order to avoid any vibrations2 possibilities to make this part:

3.1- Glue small sheets of aluminum 10 mm wide spaced 1 mm apart. (That's what I did, but I think it's not the best way because it's flimsy)

3.2- Take a 3 mm thick aluminum sheet and saw 1 mm wide grooves spaced 11 mm apart with a metal handsaw

part1 = Aluminium sheet thickness 2mm

Parts 2, 3, 4, 5, 6, 7 = Aluminium sheet thickness 1,6mm

Part 8 = saddle = T profile 20mm x 20mm x 1,6mm (to be adjust later),

1 - Mount the bridge on the resonator without the string cover with the M6 countersunk screw + washer + nylstop M6 nut. In my case, I got slight vibrations at the bridge level, so I added a circular piece of leather (diameter 7cm + a d= 6 mm hole in the center) between the bridge and the resonator . I's all fine, now

2- Mount this assembly in the guitar hole

3- Mount the tail piece

4- Mount the strings (I mounted bronze strings 12-54) , and then mount the string cover over the bridge. Pay attention to the length of the strings when you buy them because they are a bit longer as the usual standard.

In order the guitar to be playable, you 'll have to file the bridge saddle (you understand now why it is useful to be removable) , in order to measure about 2,5mm between the hight of the 12th fret and the bottom of the strings .

This iterative process is quite long.... But at the end of the end: you finished!

This project took me about two complete working days (without glue drying hours).

Now the question: how does this guitar sound?

This guitar doesn't sound like a dobro guitar and you won't be able to play great slides.

This guitar does'nt sound like a banjo

This guitar does not sound like a cigar box guitar, because there is still a sound box below the resonator.

This guitar also does not sound like a usual folk guitar because the resonator is not made of wood.

In fact, the sound is difficult to describe:

On the one hand, there is less roundness than in a wooden guitar with an acoustic wooden top, but on the other hand, it sounds with a metallic overtone, with fairly pure bass and treble sounds, but with a long envelope. It's quite original.

In order to improve the sound volume level (which is currently quite acceptable as it is), I think I will add two holes in the sound box (like in dobro guitars) in the future.

Here are some examples.

Musical tests :https://youtu.be/4kHP58Bhqg4

High frequencies : https://youtu.be/0KYYqtMOgow

Low frequencies: https://youtu.be/qDbVIpO1mnM

I was happy to give a second life to this guitar , and I hope you enjoyed reading.

Greetings from France! Bruno