Making an African Marimba

We bought our first marimbas when living in Botswana over fifteen years ago. Since then I have made new frames for them and have tried re-tuning some of the keys, but I have never made a marimba from scratch.

Making a marimba from scratch is a big project and needs good planning...but clear information about the dimensions of the different keys and the shape and length of their undercut arches is surprisingly hard to find. This is probably due to wood being a natural product that varies considerably, making it hard to create a universal guide. Whilst the concept is scientific, making keys is a bit of an art - but even so, we all need somewhere to start, so a starting place is what this instructable aims to provide.

The guide basically describes how to make and tune the keys and resonators of an African soprano marimba using a saw, a drill, a router and a few other basic hand tools. An app downloaded from the internet that allows you to compare your tuning to a specific musical note frequency is also helpful (although a piano could be used instead, of course). The whole project is a moveable feast and is not strictly reproducible in the normal way that instructables aim to be. There are many pitfalls that may make it hard to follow my guidelines to the letter - but as I say, this is a start.

Step 1: What You Will Need

Keys

To make the longest marimba key you will need to obtain well seasoned resonant hard wood that measures 5cm x 2.5cm and is 40cm in length. Each subsequent key is 1cm shorter with the shortest being 24cm long. There are 17 keys in all, so will need about 6 metres of wood. The wood should be quarter sawn with the grain running lengthwise along the key.

Templates

Template should be made from thick card or foam core. The templates are used throughout and you will need to make 17 of them. A sheet of A0 ought to be big enough.

Frame, rails and legs

To make the rails you will need 2 x 200cm planed timber 2.5 x 4cm. You will need another 2 x 200 cm of the same wood to make a frame on which to sit the rails and attach the legs.

You will also need;

4 x 1m length of planed timber 3 x 1.5cm to make the legs.

40 vine screws (long eye screws).

6m of cotton sash cord (for sash windows), or its equivalent.

4 x bolts to fix the legs in place

Various wood screws to hold parts of the marimba together. You will also need offcuts of wood to complete the project, most of which can be obtained from the pieces already listed if care is taken.

Resonator rack

You will need 4m of 3 x 1cm planed timber to support the resonators inside the marimba frame.

You will need 3m of 50mm diameter plumbing pipe.

You will need 56 nuts and bolts, with the bolts being 4mm diameter by 2cm in length, to fix the resonator tubes to the support rails securely.

You will need plastic stoppers or wooden plugs made from ply wood to seal the ends of the resonator tubes.

Marimba beaters

You will need to make marimba beaters to use during the tuning process and to play the finished instrument.

Step 2: Make a Plan

Produce a sketch or plan. It needn't have dimensions, but you need to have an idea of where you are going. This instructable explains how to make a basic two octave marimba that will play in the keys of C major and G major. It is not fully chromatic and as far as accidentals are concerned it only includes F#.

C4 D4 E4 F4 F#4 G4 A4 B4 C5 D5 E5 F5 F#5 G5 A5 B5 C6

My sketch allowed me to tinker virtually with the design which underwent a number of changes in the process of making the instrument - but you have to start somewhere!

Step 3: Source Your Wood

Source some tone wood to make the keys. That is to say, well seasoned, resonant hard wood. The wood shown above is Karagatch, a type of elm from Central Asia. Traditionally, rosewood has been the wood of choice for marimba makers but there are many more sustainable alternatives if you search around. Softwoods like pine are not suitable as they will go out of tune as the keys age.

There is no hard and fast rule about the length of the keys. There can be no strict standard because different woods have different densities, such that two identical keys made from different woods will not necessarily play the same notes. What is important is how all the keys on the same instrument relate to each other. The keys need to be thick enough to be struck without breaking, they must play sequential notes and be aesthetically pleasing to look at. The frequency that a wooden bar plays on striking depends on its length, the internal structure of its fibres, and the length and depth to which the arch on the underside of it has been hollowed out.

This instructable is based on cutting proforma keys that are 5cm across, 2.5cm thick and that range from 22cm to 40cm in length. This makes for a good starting point.

Ideally the wood should be quarter sawn with the grain running the length of the key.

Step 4: Gather Your Tools

A circular saw is really helpful as there is lots of cutting to be done and the cuts need to be square. However, the only essential power tool is a bench mounted router which will be needed to undercut the arches of the marimba keys during the tuning process. You will also need a drill and basic hand tools. An electric sander is also very useful for the fine tuning of keys.

Rounded large router bits are best to make a nice edge to the arch.

Additional useful tools include;

Lots of course and fine sand paper, and a sanding block

Drill bits for drilling holes in wood

Tenon saw and mitre block (to cut legs at an angle, for example)

Safety equipment (dust mask, goggles, ear defenders)

Wood file to assist with tuning

Wide chisel and hammer to make joints

Clamps to hold limiting blocks in place while routing the keys

Spanners to secure bolts

Screwdrivers and a bradawl or gimlet to make starter holes

Step 5: Produce Some Card or Foam Core Templates

Templates will be extremely helpful. Indeed it is hard to do without them. You can write onto them critical information which you will need to locate easily in a dusty workshop where computers don't like to go. Write on the template the intended frequency of the note and the note name, and mark lines for the nodes where the support holes will be drilled, a centre line across the middle of the key, and lines to indicate the start and finish of the arch. It is even helpful to write the length of the template on it. When you have several unmarked keys on the go, having a matching template to reference is really very useful. It is also helpful later if you go on to make other marimbas that share the same notes.

Base your templates on the wood you have sourced. The templates in the photograph were the same width as the sourced blocks of wood (5cm).

Primarily for aesthetic reasons, each template should be a regular length longer than the last. If you are following these instructions to the letter and using the same dimensions, C4 (261.63 Hz) should be 40cm long and C6 (1046.50 Hz) should be 24 cm long.

On your templates you need to mark the centre line and the node position lines before going to the next step. As a general rule of thumb, the nodes of a marimba key can be found 22.5% in from the ends of the bar. There are other ways to find the nodes, but this is a perfectly adequate method and much the easiest.

Starting with the longest template key (C6, 40cm), calculate 22.5% of this length. 22.5% of 40cm is 9cm. Draw lines across the template at 9cm from each end. Mark this as the node line. Do the same exercise for all the other templates as these lines will be used to help drill guide holes for the support cord on each key before tuning can properly begin.

A file is included on this page that provides slightly modified measurements with C6 being 23cm and C4 being 39cm.

Step 6: Make the Rails, Attach Vine Screws and Cut Your Keys

Purchase some planed timber softwood suitable for making rails to support the keys. Each piece of timber should be 2m long, 4cm deep and 1.5cm wide (i.e. wide enough and deep enough to take a vine screw without splitting). The rails in the photograph above are a little heavier, being 2cm wide and 5cm deep. The wood can be trim routed to remove sharp edges. Draw a line along the top of each rail, marking the centre line.

On a work bench, lay out the template keys as if they were the real keys on a marimba. Line up the mid lines and adjust each 'key' so that it is parallel to the last and separated from it by a gap of 1cm. Spacers made from card or foam core make this quicker and easier to do.

Once the template keys are positioned in their correct places, lay the rails onto the templates in such a way that the rails more or less cover up the node lines of each and every template. The rails should overhang the end of the templates at one end by about 10cm. There should be plenty of excess wood at the other ends which can then be cut off and used to make the end rails that will ultimately hold the rails apart, completing a trapezoid frame that has greater intrinsic strength.

You can start work on making the cross rails straight away once you are confident of the length your rails must be. However, if you prefer to do this later, you can temporarily screw some wooden batons to the end of the rails to keep the spacing correct while you work on cutting the keys to their correct lengths.

Mark on the rails the intended position of each key. There will be a centimetre space between the widths of each key, with the centre line of the rail running through it. Mark the centre point of this space and then, using it as a guide, drill a hole for the vine screw that will ultimately support the cord that holds the keys away from the rail. Use a 2mm drill bit.

Screw in the vine screws, leaving the eyelets proud of the rails by a couple of centimetres. Run the sash cord through the eyelets and tie it off to make a supporting cord onto which you will be able to place the keys temporarily once you have cut them (it doesn't need to be extremely tight at this stage).

Now, using a circular saw cut the keys to match the lengths of the templates and sand off any rough edges. Place the un-tuned keys onto the cord at their correct locations and using your marimba mallet or screwdriver handle wrapped in cloth, strike the untuned keys to get an idea of their resonant quality.

When the bars are cut to these dimensions they will generally play a scale of sorts, but un-tuned bars of cut wood will produce higher sounds than the intended notes and the ringing tone of the wood will be very short lived. It would be a miracle if the keys were in tune! Tuning requires wood to be removed from the underside of the bar to make the bar more flexible and lengthen the sustain of the tone produced. Tuning ultimately determines the note that the bar plays (and also whether it is thick enough to withstand being struck).

Step 7: Make Your First Keys

Place your template on top of its corresponding key. Using the node lines on the template as a guide, mark a drill hole half way down the side of the key and, using an 8mm drill bit, drill a hole through from one side of the bar to the other, trying to keep the hole 'level' to follow the line of the node. Repeat at the other end too. These will be the holes through which a cord will run to suspend the keys over the marimba rails.

Now that you have drilled your holes, suspend the key from one end by holding it between your finger and thumb at one pair of entrance and exit holes. Strike the key again with a marimba mallet (or the wrapped screwdriver handle). This will give a reference for the pitch the bar produces in its untuned state.

Next, mark pencil lines on both sides of the key at 25% from the ends of the bar. These lines mark the extreme ends of the 'arch' of wood that will be cut away during the tuning process. A mid line at 50% is also a useful reference.

Using the router, remove wood from the underside of the key. Start by removing a maximum of 0.6cm of wood with a rounded router bit from the underside of the bar. Do not cut beyond the 25% lines. Smooth off with sand paper and then strike the key again to register the change in pitch.

Raise the router bit to 1cm and remove more wood. This time work on the middle 20-30% of the bar (10-15% either side of the midline). Again, test the frequency the key now produces against a known reference source such as a piano key, or the sound of the target note from a signal generator app. Two cuts is usually enough, but if a third cut is necessary, step up to, say, removing wood from the middle 10% to 12mm.

Keep sanding after each cut. As you approach the target frequency it is very very easy to cut away too much wood and ruin the key. Change to using a belt sander (or sander bit on your drill), or a sanding block or else use a file to smooth out a very shallow channel from the centre of the bar. Keep checking the note produced by the bar against your reference until you are within about 20 or 30 Hertz sharp. Stop and allow the bar to cool before trying to get to the reference frequency by hand sanding.

Once you have made one key it does get easier and faster. Keep making more keys until you have made all 18.

Step 8: Make Your Resonator Rack

The resonators in the picture above are for a tenor marimba but the principle of their production and suspension is the same. The file included here is the same one from a previous stage of this instructable but this time we are looking at the resonator pipe lengths.

Each pipe must be a quarter of the wavelength of the note produced by the key sitting above it. The table shows frequencies and wavelengths of the keys and the lengths the pipes need to be cut to. Resonator pipes should be closed with a stopper of some sort. Quarter wavelength closed pipe resonators will resonate with the key as it is struck and will increase the volume and sustain of the note produced.

Cut the pipes carefully with the circular saw.

Lay the support rails across the top of the marimba keys when they are mounted on the rails. Using the keys as your guide, mark on the resonator suspension rails positions for drill holes. Mark two holes on one rail and one on the other for each resonator tube. Three bolts prevents the pipes swinging and loosening the nuts over time.

Drill through the rails first using the 4mm drill bit, then use these holes as guides to drill through the pipe walls after positioning each pipe level with the top of the rail. Add nuts and bolts as you go to keep everything firmly held together.

After attaching all the pipes, cut plugs or stoppers from some ply wood to seal the ends of the pipes.

Once the frame of the marimba is built you will be able to cut the rails of the resonator rack so that the rack drops into the frame but can be removed later for easier storage.

Step 9: Make the Frame

This picture shows the basic design of a crocodile style marimba frame. The key rail is currently devoid of vine screws or keys, and is attached to the outer frame at one end by a door hinge. The legs are also bolted to the outer frame.

Wooden blocks must be cut and attached to the out frame using screws. These act as chocks that prevent the legs from splaying out further than the desired angle, without restricting the legs from folding up against the frame.

Cross bars can be used to join and strengthen the integrity of the legs as they swing out. This is all basic carpentry that does not need much explanation. However, this frame is quite different to the frame in the original drawing from the first stage of this instructable, so let me explain why.

In the original design the legs were attached directly to the tapering rails. However, when making the marimba I found the legs too wobbly when attached this way. The problem was the small area of contact between the legs and the rails at the joint. Tightened the legs parallel to the rails gave more contact area between the top of the legs and the rails, but prevented them folding in and out because of the tapering angle of the rails. If I splayed them outward to allow folding there was very little contact area either side of the joint, making the joint too unstable ...and since the joint was held by metal bolts that would ultimately wear the wood away with continued use if there was any flexibility in the joint, I felt it needed a design change. I could have cut off a little from the inside of the top of the leg to make the contact area larger, but I preferred another approach. In the end I came up with what I've called a 'crocodile' design.

To the original design I added an outer frame around the rails. I attached the legs to this frame in parallel, making the leg hinges tight and firm. I also attached the rails at one end using door hinges. This had the benefit of allowing me to open the 'mouth' of the crocodile and drop the resonator rack in from above. In my tenor marimba, which doesn't have this feature I still have to wrestle with a heavy resonator rack to insert it from underneath. When working on my own, it's generally easier to lay the instrument on its side to achieve this, but this is not the case in this soprano marimba. That said, the soprano is heavy as a result of the extra frame. Without the resonator rack in place the two instruments weigh about the same even though the tenor is longer, higher and uses longer keys.

I'm sure the design could have been modified differently to solve the problem but in the end I am happy with the way it has turned out.

Step 10: Putting It All Together

Once the frame is complete and the rails are in place, add some wooden shelves to the underside of the frame at both ends that overlap the ends by a centimeter or so. Screw these in place. The shelves will provide support for the resonator rack.

Cut the rails of the resonator rack to the correct length so that the rack can be dropped onto these shelves, placing the resonators in their correct positions below their respective keys when the 'crocodile jaw' rails holding the keys is lowered into position.

Finally, make some beaters using 30 cm sticks of 1cm diameter dowling onto which have been stuck 2cm long blocks of rounded wood cut from a drawing pin or thick broom handle. Drill holes in the wood blocks, add glue to the holes and slip the wood blocks onto the dowling so that a 1cm length of dowling protrudes. Next, tie a ball of yarn to the dowling underneath the block and proceed to wrap the yarn over and under the wood block, turning the stick as you go so the the yarn begins to wrap around the wood block and cover it. Wrap for at least 250 cycles so none of the wood block remains visible. Once you are happy, cut the yan and, with a darning needle, pass the loose end through the wrapped yarn over and over and over again at the top and bottom of the block so that it all becomes tightly amalgamated. Finally thread the loose end into the mass of yarn and remove the needle. Make two such beaters.

There are instructions elsewhere on instructables on how to wrap your own marimba mallets if you need assistance on this.

That's about it. I made another marimba too - a tenor, but you can follow how that was done elsewhere on the internet.

Step 11: Carry Out a Sound Check...

Here is my first run through of a couple of familiar tunes. The soprano isn't quite as mellow as I would like it to be - perhaps if I had used rosewood rather than karagatch it might have been a little longer in the sustain. Also, I am not confident that I have the resonator plugs set at quite the right height since I finished the instrument off a little hastily. That said, whilst I don't claim to be a musician, I think this sounds okay for a first tuning. One or two notes still need some very minor adjustments though....

The second video is of a small group of players who I had the pleasure to teach at my school's summer school. They are Grade 5 and 6 and got just a forty minute lesson to start. None of them play musical instruments but with a bit of coaching they got quite proficient. Ayaru plays the tune on the soprano, Ayana plays below her and sets the tempo. Marzhan plays the bass line on the lower tenor, with Aigerim (top) and Amina (middle) accompanying on tenor harmonies.