Tuning and Sanding the Bars for the 5 Octave Marimba

By Jim McCarthy | May 7, 2009

Welcome back marimba building enthusiasts! The last installment of this blog saw me at the point where the bars had all been cut and sanded in a basic way – basically to the correct dimensions. The next steps involve doing the basic tuning – then doing the finish sanding/polishing – then some tricky bits involving finding nodal points and providing a good average layout (more on that process later) – then finally the drilling and fine tuning.

By far the bulk of the actual work is the basic tuning and sanding and let me tell you it creates a LOT of sawdust! Because of this you really need to do it in a workshop or even better – outside! Well I’ve been a bit hampered by rainy weather over the last couple of weeks, so work has been sporadic, but these two tasks are now ALMOST done.

some marimba bars roughly tuned and sanded

Let’s have a look at some of the steps. Above is a photo of some bars that have gone through the basic tune and sand process. This involves routing or sanding the arch under the marimba bar in the appropriate places to get the fundamental tone and any harmonics you want to also tune to the correct harmonic relationships with each other and also all down to about one semitone above the final pitch.

Below is a photo of my laptop all covered in gladwrap plastic to protect it from the sawdust. I’m using the fantastic Peterson Strobosoft II deluxe software which makes tuning even the higher and short lived harmonics much easier than pretty much anything else I’ve ever used.

tuning marimba bars with a software stroboscope

At this point there is minimal chance of knocking the bar about anymore, so I use 80 grit sandpaper on the orbital sander to go over all the bar surfaces and smooth them out, making sure there are no leftover scratches from the coarse sandpaper. This will lower the bar pitch a little but that’s ok as we started with a whole semitone to spare. After this, it’s back to the sanding disc and the bar is tuned down to the point where it actually reads the correct note – but only just! – In other words about 40 cents (40% of a semitone) sharp.

The next stage is the fine sanding and finishing of the bar faces (particularly the main top face). This can be easy and fast, or very time consuming, depending on the level of finish you want to obtain. I’m personally going for a highly polished finish, there have been many hours of work. The idea is to use sandpaper on a sanding block and sand the bar by hand using gradually finer and finer sandpapers. I start with 120 grit paper and work my way up in about five steps to 1200 grit paper. The photo below shows six bars that have been through the fine sanding process.The bars on their edge to the right of the photo have not yet been hand sanded.

marimba bars after fine sanding process to 1200 grit paper

Next comes the polishing of the marimba bars. For this I use Marveer furniture timber polish. You can use any non-silicone based polish. It’s essentially just a light oil. Moisture will tend to raisethe grain of the timber a little, so to counter this as well as a final abraisive stage, I actually use a fine steel wool to apply the liquid. I bit of “elbow grease” is required – each bar gets rubbed firmly for a few minutes with the steel wool till the polish has soaked in thoroughly all over. Then a soft cotton cloth is used to wipe off the residue then apply a little more polish which cleans any excessive fine wood particles away – then dry the bar. This photo below shows the lowest few bars all polished – note the dark red colour has been brought out of the timber.

the low marimba bars after the polishing process

As I get all the bars to this finished point, I’m laying them out in sequence on top of my 4+1/6 octave marimba in the studio. You can see from this photo that I’m almost done with this process, with just the top two octaves (with much smaller bars) to go. The extra bars at the low end have just been stacked up. This keeps me motivated as it’s exciting to see what these bars will look like when in position on an instrument. I’m really loving the colour of this particular batch of timber – particularly the middle bars which have some colour variation and patterns on some bars – a bit like a Jersey cow!

marimba barsfor the 5 octave marimba layed out in position

Keep reading here for updates all! Next will come the node finding and finding of suitable frame measurements. When the instrument is done you will be able to get the comprehensive building guide from www.makeamarimba.com

Jim McCarthy

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Five Octaves of Marimba bars cut & faced!

By Jim McCarthy | April 20, 2009

Hi all – today was a very exciting day – or to be more accurate the last 3 days have had an exciting result!

Yep it’s taken me way longer than normal to do the task, but now I have the raw timber cut into five octaves worth of bars all the correct dimensions, and all planed and sanded smooth. It took much longer than normal for this usually quick and simple task because the timber stock I started with was in a pretty basic form. All the edges were very rough and the planks has not been put through the planers at the lumber yard – or even the thicknessing machine. The planks therefore all had very uneven surfaces.

There was quite a bit of work to be done with the plane, then the coarse sanding disk, then the orbital sander with a coarse (40grit) paper to get the bars to an essentially uniform shape with reasonably smooth faces.

It’s raining for the next few days, so I won’t begin tuning yet but that task is next – keep an eye out in the next week!

5 octaves of marimba bars cut to sizer and sanded smooth

5 octaves of marimba bars cut to sizer and sanded smooth

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Introduction to the P 4 to 5 Octave Marimba Project

By Jim McCarthy | April 15, 2009

Hi all – Jim McCarthy here – designer and builder of percussion keyboard instruments. 

YOU can build your own marimba, vibraphone, xylophone or glockenspiel. My design philosophy is to create instruments that are as good as commercial ones, but which require NO special tools or materials. You can see some of the the other instruments and materials I’ve produced at the home page here at www.makeamarimba.com

THIS blog is going to be a step by step following of the building of the latest design – the P4to5 Marimba. Its a professional quality concert marimba which can be built to any range from four to five octaves. I’m going to build the full 5 octave version.

Unlike the other building projects which were built quite quickly, this one I am going to do more gradually because I’m just so busy this entire year and have little in the way of continuous blocks of time to spend on it. So this blog is designed to keep you all up to date on my progress. Of course at the end of the project there will be a fully detailed building guide available with all the info required for you to build your OWN concert marimba.

The designs have been in development for several months and are basically sketched out – so the first major step was to purchase the timber for the bars. The traditional best choice for marimba bars has always been Honduras Rosewood (Dalbergia Stevensonii) but it is really difficult to get hold of here in Australia. As it is no nonget legal to import it into the country it is down to what you can find already here – not much! – and it is REALLY expensive. As it happened the was a specialist timber yard locally who had a reasonable amount of African Padauk in stock – the SECOND best timber choice traditionally – so this was the obvious choice. The stock was 100mm x 45mm and came in 3m lengths I was able to get the yard to put the planks throught the massive bandsaw and get it cut through the thickness. The saw blade was 3mm thick so each stock piece yielded 2 planks 21mm thick – just 2mm over the 19mm (3/4″) which is the required bar thickness. Perfect by the time it is to be cleaned up! I purchased 3 stock pieces which gave me 6 planks – about one more than actually required but it always pays to have extra as there is always some bits which are not useable due to splits etc.

Here’s what it looks like all rough and covered in a few years worth of dust from the stock yard! More comign soon when it is to be cut into bars!

Raw Planks for the marimba bars

Raw Planks for the marimba bars

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