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.
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.
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.
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.
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!
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