Making an Alummium Surdo: The Story

The Story

Introduction
After looking more closely to the instruments I was playing on, I couldn't help thinking about making my own. This was partly due to my precarious financial situation and partly because of my curiosity as a mechanical engineer. "It shouldn't be that hard", I thought. Well, it wasn't, but not everything smoothly.

The first step was to find a workshop of some kind. I did have access to a workshop at university where I knew my way around quite well. Unfortunately, I did not have the time to do something other than work on my graduation project. When I graduated, I moved 200 km away, so that was an option less. After asking around, a friend, Tony, arranged it for me to have a sheet of aluminium rolled in the workshop of the company he works for.

As I did not have much of an idea of how to go about things, I asked some questions to the sambistas mailing list. There I got some valuable information to start with. From Michel Nicters I got very useful information on the practical side of manufacturing.

As a guideline, I took a 12" repinique and just adapted the measurements. Because of this, I decided to make the surdo in steps. After finishing one of the steps, I would go on and make the next part, thus ensuring that everything would fit and, in case of failure, I wouldn't be stuck with a lot of useless material.

Shell
The first question was what the weight of a surdo should be at most. The total weight should not be more than about 5 kg, or else it will get too havy to walk with it.
Several suggestions were made for material and wall thickness of the surdo. Wood would be very nice, but I did not have any means of getting it in the right shape. Other possibilities are steel and aluminium sheet. Steel is cheaper and stiffer than aluminium, but also heavier. It would require a thin wall when using steel, 0.5 or 0.75 mm to keep the weight down. As there might be a problem with buckling, I chose to use aluminium.

The next question was the required wall thickness. I was divided between 1 and 2 mm. 2 mm would give a surdo-shell of about 5 kg, without rims. 1 mm would mean 2.5 kg.
I discussed this and other issues with Michel. He could get hold of a 2 mm sheet large enough to make a 12" repinique. To find out if it could work and what the unexpected practical problems would be, I decided to make a prototype repinique-shell and test it using the rim and tension-rods from another repinique.

Making this prototype was very useful. The edges of the shell, which need to be rounded in order not to cut the skin, were made by simply bending both long edges of the flat sheet and then rolling the sheet. The radius formed for the edge was of about 2.5 mm, similar to that of commercial repiniques. It proved to be a very elegant solution. Rolling the folded sheet was not too difficult, although I had to resign to the fact that I could not get it completely cylindrical because we did not have the right equipment. Most rolls leave the ends straight and unbended. The solution is making the sheet extra long and cut the first and the last part off, giving the right size. I just bent the last ends by hand. To connect both ends, I just made a recess and slided both ends over each other. To fasten it, I used rivets. Make sure to use sufficient rivets (I used one every 5 cm) and that both plates are clamped together firmly during riveting, otherwise you might get rattling from loose material.

This prototype took some time to finish, as I did not have the right tools and was somewhat discouraged by it. After a some "persuasion" by and help from my brother and yet another friend, Alex, the repinique-prototype was finally ready. After the first session, it became clear that is was a heavy repinique, but that it worked well. Encouraged by these results, I decided to go on and make the 20" surdo.

After some asking around, I found suppliers for the required materials. When we were in the warehouse, buying material for the tension rods, we had some doubts about the size. We had a 6 metre long rod we needed to cut to the right length to fit in the car. After sawing off the first end, it seemed a bit short. I had calculated a height of 60 cm for the surdo. We were seriously doubting this size, so much, that, before cutting up the rod and the sheet, we called a friend, Marcel, and asked him to measure his surdo. He confirmed the 60 cm and we went on. A good thing, else we might have ended up with a 90 cm high "mega"-surdo. It was probably the size of the hall and the material that made us doubt.
After this, once again, we went to Tony's company, now with a larger aluminium sheet. As we have a small Ford Fiesta, we had a little trouble with the transport. We had to drive with the sheet held over our heads and sticking out of the back. My brother noticed several other drivers laughing at us when we passed by. Despite this, we managed to get to the workshop safely.

As the weight of the repinique was too large, a surdo would become too heavy if made from 2 mm aluminium sheet. After having a better look at commercial surdos, which are made from 1 mm sheet, I decided to do the same. The shell was made in the same way as the repinique shell, but the only problem were the rounded edges. With the 2 mm sheet, the folded edges gave a large enough radius. With 1 mm sheet the edges might become too sharp and considerably shorten the lifespan of the skins. Regular instruments have an edge made by folding the sheet around a round metal wire. This is also what I tried to do. Halfway folding the long edges, the metal wire was laid along the fold and the edge folded further. This was tricky and did not give the result I hoped for, but we managed to get an edge that is probably sufficiently rounded.

By the way, make sure that the edges are smooth. Scratches may diminish the lifespan of the skins.

As I only got the skins after I had rolled the cilinder, I had made an educated guess on the diameter. I took the largest possible diameter and could always trim it down if necessary. When I got the skins (which were somewhat delayed...) it was indeed necessary to trim the edge, but nothing too dramatic.

After connecting the ends, we had to find out about the size and position of the air vent hole. We had a somewhat strange telephone conversation with Marcel when we asked him about these measurements. In Dutch, it is somewhat strange to ask for the size of somebody's hole ("gat") and the position of it from the seam ("naad"). We had a bit of a "low-level" conversation. By the way, we drilled a 8 mm diameter hole 26.5 mm from the bottom end.

Skins and stick
These were the only parts that were not "Home-made". The neighbours' cats were too fast fo me to get a skin..... Kidding aside, I don't think I could make a good quality skin myself. Who knows, I might try this in the future. Because I didn't know if it would work, I used ordinary plastic skins. After a while, I bought a nappa skin hile over in Brazil, which works reasonably well.

The stick can very well be made from a broomstick and a wooden door-knob with some rubber and cloth glued and wrapped around it, but we just didn't feel up to it and bought one. Maybe later.

Rims and tension rods
The tensioning rods were made from 6 mm round steel rod. At one end I cut M6 metric thread. By the way, apparently Brazilian instruments are made using imperial thread. The other end was flattened by heating it and hammering. I had this done at a local blacksmith, as it would take too long to find someone to find a good heater.

The rim was made by rolling 15x3mm strip to size at Tony's company and the ends were welded together at the workshop of my former university. I went to visit a few friends back at university and took the liberty of using the workshop of the department. I had roamed around there for 8 months so I knew my way around. The attachment points on the rim for the tension rods were made from M12 bolts. First, 8 holes were drilled in the ring, then thread was cut. When the bolts were in place, I drilled holes in them. After that, the head and end of the bolts were cut off. The reason for using bolts was that I did not have access to a lathe to make simple ends. Although I had all the equipment I needed at hand in the university workshop, it still took me more or less a full day to make the rims and cut the thread of the tension roda. Cutting the bolts and finishing off the tensioning rods were done at a later stage by Alex. He got one of his fingers quite burnt when doing this, but now has completely recovered.

The finished surdo.
Click for a larger
version (49k)

At this point, the basic shape of the surdo was there. We assembled it and tried it for the first time in the kitchen, which we were using as workshop. It sounded good and, for me, that was quite a relief, as I had no idea what it would sound like. With the plastic skin, it sounds somewhat harsh, but acceptable. With a nappa skin, it sounds reasonably good.

One litlle imperfection is the part were the two ends of the rounded aluminium sheet meet. As they were not completely rounded, and there was a slight gap between the ends, these ends that were already bent towards the centre of the skin were also pulled by the skin even more to the centre, leading to lower skin tension around the area. It appears not to affect the sound too much. How this will influence performance in the long run, I don't know.

In general, I wonder how this surdo will stand wear and tear. I have not calculated any forces, as I just basically "blew up" a repinique to surdo size. It might very well fall apart after a few times playing. If that happens, I'll let you know in these pages. One thing I learnt is what the tricky parts are to manufacture and therefore what to look for when buying a surdo. The first thing I noticed when I looked at the cheaper surdos in Brazil was that these are not always cilindrical, especially near the connection.

After some final adjustments, such as improving the rounding of the rim by hand, filing and sanding the rough edges and painting it, the surdo was finally finished. Now I have no excuse not to practice or loose the beat.

Acknowledgements
I would like to thank the following persons for making the surdo possible:
Antonio del Aguilla Roman, Michel Nicters, Alex and Jos van der Weijde, Marcel Spong, Francisco Müller, the foreman at Ravo, Jan Kaspers, Bertus Droger.
The people from the sambistas mailing list and anyone I might have forgotten.

The surdo is, of course, IAF-approved.

I will be happy to answers questions or discuss matters related to surdo-making, time permitting. For that, drop me an e-mail.