By Jim McCarthy | July 9, 2009
Welome back marimba building enthusiasts! In this installment of the 5octave marimba building blog I’ll go over some details of the final stages. I’ll cover:
- Staining and coating the frame with estapol.
- Spraypainting the resonator banks – you won’t believe they’re not metal!
- Using felt lining and rubber tubing to keep all the joints rattle and squeak free – you hear JUST the marimba!
- A better and faster way to produce the aluminium bar posts so that they look completely professional.
- Putting the bar posts and string tension posts into the horizontal struts, and putting on the protective felt strip.
The painting of frame and resonators is a time consuming task. It takes a while to do anyway, but then there is also drying time to consider and the fact that everything needs more than one coat. The resonators in particular caused mean issue because it is not summer here at the moment. As I have to spray paint outside, this means I am at the mercy of the weather quite a bit. It needs to be warm enough for the paint to stick well and dry properly in reasonable time,and it also needs to be fairly wind free conditions to have any hope of getting the paint where you want it. It took me about a week to get the resonators done even using paint which could be recoated within the first hour of drying. The basic idea is to lay out all the resonator banks on a flat surface – in my case on a large sheet of plastic so overspray would not paint my tables underneath. Then spray a first coat over all the surface possible. You wan’t to get as much paint on there as you can without it running in drips – better to have morecoats than a bad job. It can be tricky to get paint into the gaps between the tubes,so it is usually better to start spraying into the gaps fromone side then the other before spraying the outside facing faces. The paint I was using allowed a recoat withing the first hour or after 8 hours, so I was sure to come back about 45 minutes after the first coat and thicken it up a little. The next day I turned the resonator banks over so that the unexposed bits were now showing, and repeated the process.
Because of the shape of the banks, some of them needed to be coated from three or four different angles to fully cover all the visible surfaces. I also like to spray quite a bit inside the tube mouths as this makes them look a lot better from the top – even with the bars in place over them. Once all the surfaces were covered, quite a few of them needed another coat. One thing I have learnt doing this task over the years, is that the quality and type of paint you use plays a major part in the result! Better paint can be more expensive, but it is usually well worth it. It sticks better, dries better, looks better and usually wears better as well. By this I mean that it won’t chip and scrape off with the slightest touch. I have also found that a coat of plastic primer can help this stickability when painting plastic pipe, so I gave all the banks a coat of this stuff here in the photo before the paint.
The timberwork was not so much of a problem, as I was brushing it on. This meant I could do it indoors as long as there was decent ventilation. I also wanted to stain the frame timber. Partially because I just wanted a darker, browner colour to contrast more with the reddish colour of the bars, but also because the timber of the frame varied in colour quite a bit. I used Australian Oak for some bits and Meranti for others. These were quite different, but even the Meranti planks provided quite a variety of colour in themselves. SO…. To both save time and help with the colour differences, I used a 2 in 1 estapol stain product. I like this product for this job, as it has a way of putting the colour on top of the surface rather than soaking into it – particularly on the second coat. This means it tends to bring the different colours closer together. Of course it also means there is one job not two. Great! You DO have to be a little more careful in the application though to avoid streaking and blobs of colour. You need to brush everything very evenly. After a first coat, a light sand with fine paper prepares the surface for a second coat which goes on smoother and darkens the colour further. You can see the result in the photo here. I’ve used a satin finish rather than a gloss finish here as it tends to be more forgiving looks wise of the odd scratch etc. It’s probably a good idea to put a third coat of estapol on any parts which will wear particularly. I like to use normal clear estapol for the third coat,as it means that if it DOES get a little scratch or scrape then it is not taking the stain colour away and is less visible.
After all the timber parts were dry, the next step was to glue on some bits of thin felt to the surfaces that would be touching each other when assembled. This is particularly important at the ends of the more diagonal horizontal bar support struts as they tend to be bounced direcly when playing, but unlike the inside struts in this particular design,they are not actually held firmly to the end sections with bolts – they just rest there. I also like to line the parts that ARE bolted together anyway – it doesn’t take long in the scheme of things when you consider the time spent overall. You may actually remember from previous blog entries, that when fitting the struts to the frame end pieces at various points in the construction, I left a little extra room to allow for the thickness of this felt which I had already purchased in advance, so I knew how thick it was exactly, and so knew how much extra gap to allow.
The resonators are also prime candidates for causing squeaks and rattles – mostly at the points where the ends of the banks meet each other and/or the supports that hold them up.The most effective solution in this case is to stretch some thin and soft rubber tube over the ends of the aluminium flat that form the ends of the resonator banks. This isolates them from each other, and also from the supports in one step. Once again – I had my specific tubing sorted out before I started construction on the marimba, so I knew how much thicker it would make the aluminium strips at the resonator ends. This was important, as the slots for them had to be cut out from the aluminium cross supports.Also the ends of the resonator banks needed a little bend in some cases to tweak them to the perfect gap so the smaller banks would fit neatly inside the bigger banks. See the photo here. Also of course at the small end section of the frame, the little timber block needed to be cut allowing for this tube also.
Now normally, my first port of call for rubber tubing and similar things, is my local rubber supplies shop which stocks just about everthing . In this paricular case however there didn’t seem to be anything available in a soft walled tube that was big enough to go over the 25mm wide aluminium – or at least that wasn’t way too thick. I searched online and did find a place that sold larger diameter silicone tubing with a thinnish wall,but it was REALLY expensive and had to be shipped from overseas as well. The solution in the end was simple and cheap. The local bike shop sold me an inner tube – the sort I used to get punctures in all the time! I found the correct diameter tube and it cost me $6.50 – one tube was more than enough for the whole job.
Now it was time to get all the little string holding bar posts fixed into the struts. Actually – although I had already made a few of these using nothing but a drill and an angle grinder, I wanted to make the rest a faster and better way. For those who don’t have access to more expensive workshop machines, the simple method shown in one of my previous posts actually works quite well,and you get reasonably fast at it. Theres about 150 of them ona 5 octave marimba though, so it’s worth using a good process if you have it available to you.
The photo here above left shows a superior way of cutting the round ended slot that the strings sit in – using a milling machine with a 4mm mill bit. It is a simple matter of measuring and marking the point where the slot should end,then setting up the clamp so the aluminium strip is centered on the bit. The mill then only has to travel in one direction to cut a single short slot. You can see from the photo of the finished product to the right, that the mill cuts a really nice and uniform slot with straight sides and smooth edges – no rough bits. The cut outs at the bottom COULD be done with the mill also, but there’s a faster way which also creates hard 90 degree shoulders rather than the rounded ones milling would leave. A band saw is the short cut! Milling would leave a better finish, but I opted for the faster option as these bottom bits are not seen anyway – they are hammered into the timber horizontal struts.
The aluminium bar posts are not strong enough to hold the tension of the strings at either end where it bends 90 degrees and completes the loop. They are designed to hold the string up – not resist tension sideways. Soooo we need a stronger post at each end of each strut for the string to pass around. I kinda like the look of the brass alan key bolts which I used for the resonator height adjustment and cross struts, so I decided to use these for the end posts. This also adds a look of consistency to the whole affair. These are simply hammered gently into holes drilled into the struts with a little glue to hold them in place. You can see one of them in the photo here above left.
This photo here to the right shows one of the bar posts in position on a strut and complete with a bit of rubber tube around it. The rubber tube is important as it is a soft layer between the side of each bar and the metal of the bar post which prevents rattles. For this instrument I’m using a continuous strip of adhesive backed felt stuck on top of each horizontal timber strut. These are not strictly needed as the bars should be held up high enough from the struts that they never touch – BUT – experience tells me that on occasion with a slightly loose string and a bar hit hard close to the string, the bar will flex down just enough to touch the strut and make a horrible clunk sound. The layer of felt prevents these clunks. A little slot is cut with scissors in the felt for each of the bar posts at the points where the holes are drilled in the struts. Each bar post is gently hammered into the holes through the felt with a little glue to hold it in. The self adhesive felt sticks on pretty well by itself but the bar posts really hold it on firmly. Each post is fine adjusted to the perfect angle with pliers before the tube is put on.
This photo to the left shows some of the results from this week’s efforts all put together. You can see the resonator height adjustments adjusted to a high position. Everything is starting to look pretty good now that the finishing touches are coming on and everything is going together in the proper positions.
Next post will see me finish stringing the bars and the final steps.