20" dia x 50cm deep
Made from 5mm flexible plywood. Excluding the skins it cost me around £68 with enough wood left over to build a repinique for £9 (cost of extra aluminium).
I put a Fibreskyn head on the top and a nylon head on the bottom. The sound is wonderful.
Construction does not need access to a workshop, and is well within the capabilities of any keen DIY'er with a few tools.
Gerhard Totschnigs excellent drum building page is no longer available, so following requests from many people I have put together this page of instructions, based on Gerhard's original material and my own experiences. Many of the pictures below are from Gerhard's original web page, plus a few of my own.
Mail me if you'd like to discuss any aspects of construction.
If you have difficulty finding 8mm M5 countersunk socket screws in the UK, I can recommend A2 A4 Fixings Ltd in Southampton.
Flexible plywood in the UK is available from William T Eden.
Vertical drill stand (essential), router with 45 degree cutter, home made bar bender (see below), deep throated G clamps (at least 2 deep ones and a couple of regular size), plastic spring clamps (maybe 30 of these), mechanical metal saw (not essential but if you cut a bar with a handsaw you can spend too much time filing the cut end to get a flat 90 degree end on the bar), jigsaw, circular saw (not essential but better for a straight edge than a handsaw).
Actual dimensions for the following materials will depend on what size and depth drum you are going to build.
M5 threaded bar (3 pieces at least 25cm each for the frame), M5 wingnuts (6 of, but regular nuts would do), M5 self locking nuts (16 of), 8mm M5 countersunk socket screws (20 of), M5 nuts (4 of), 6mm aluminium rod for the tensioning rods, 12mm aluminium rod for the tensioning bolts, 20mm x 3mm aluminium bar for the counterhoops.
18mm or 15mm (but no thinner) cheap construction plywood for the frames, 5mm flexible plywood for the shell (easiest ply to work with, you will need to allow extra for the reinforcing strips, and bear in mind which way the ply bends!), two lengths of 25 x 25mm (approx) hardwood - for a 50cm deep drum these should be 60cm long - used to compress the glued joint of the shell.
Making the bar bender
This simple but effective device can be made out of any scrap materials but you will need some nuts and bolts, and 3 hard plastic wheels about 50 or 60mm in diameter. I got some utility / furniture wheels from a local DIY store. Make sure their rim is fairly flat or with a minimal curve else the bar will move around as you work it. The pictures below of the one that Gerhard built and my own version should explain enough of how to make one. Gerhard used metal for his, I used two flat pieces of aluminium for the sides, screwed to a hardwood block in the centre.
First buy your drumhead
The shell and counterhoops are built to fit the head, so you will need this to work out your measurements.
For the plywood, measure the internal diameter of the aluminium ring of the drumhead and subtract 4mm to allow for a good fit. Now we need some maths, the circumference is equal to the diameter multiplied by Pi (C = D x 3.14) or (C = D-4 x 3.14) allowing for the 4mm, BUT when you bend plywood the inner surface compresses and the outer stretches and you need to account for this. The formula should now be (C = D-4 x 3.14 MINUS T x 3.14) where T is the thickness of the plywood. As an example; say the internal diameter of the aluminium ring on the drumhead is 557mm and I'm using 5mm ply, (C = ((557-4) x 3.14) - (5 x 3.14)) which works out at 1720.72mm, so round it to 1721mm.
For the depth, I built mine 50cm deep, so I would need a piece of ply 1721 x 500mm BUT you are going to need some extra for the reinforcing strips around the top and bottom inner edges and a central vertical strip over the joined edges of the shell. These strips should be 50mm wide, so the centre piece would be 40 x 5cm (think about which direction it will have to flex before you cut it!) and the top and bottom strips 50 x 1720 (or thereabouts). When buying your plywood, most retailers have a board cutting service, so give them your measurements for a perfect straight cut edge where the join will be.
This picture shows how the frames should be cut out and you will need three of these. The slot at the top is for the 25 x 25mm hardwood beam used to compress the glued join (but don't put glue on the edges that butt together or they will stick to the hardwood beam). To draw an accurate large circle, nail one end of a thin strip of wood to the centre of the sheet of construction ply. Then cut a small notch at the required radius, with a pencil tip in the notch, draw the circle.
Place the 3 frames on top of each other, with the outer compression beam inserted in its slot. Insert the flexible ply shell then pull the top frame up to about 10cm below the top edge of the shell, and evenly space the middle and bottom frames.
Tighten evenly the wingnuts on each frame to bring the edges of the shell together. This is easier done with the shell and frames on their side.
These 3 pictures show the inner joining strip and reinforcing rings all glued at the same time with all the clamps in place. I found it easier to glue the 5cm joining strip (allowing a 5cm gap top and bottom for the reinforcing rings), allow the glue to dry and then remove the big clamps for better access when glueing the 5cm wide reinforcing rings. You will need at least four and even better six deep clamps to compress the joining strip between the inner and outer compression beams.
When gluing the inner reinforcing rings, the clamps around the edge should be no more than 5cm apart. Don't clamp both ends of the ring to start with or you will get problems; start at one end and clamp at 5cm intervals working your way around to the other end, this ensures that the ring lies level with the shell edge. I used spring clamps rather than screw handled clamps for this as they are easier to adjust.
Make sure you use plenty of clamps or you can get poor adhesion in places, as shown in this picture. When the glue has dried remove all the clamps, but leave the frames in place, and stand the shell on a flat surface to check that it is level with no high spots, if there are any then level them with some sandpaper.
Now we use the router with a 45 degree cutter to cut the bearing edge at each end of the shell. Loosen the end frames and pull them up flush with the ends of the shell. This will provide a level surface for even cutting with the router. Remember which direction to push the router or you will get a lousy cut. Your aiming to get an edge about 3mm wide.
Smooth off all edges with fine grade sandpaper, then drill a 10mm vent hole halfway down the shell oposite the join. You can then hang the drum from this hole in order to varnish or paint it.
Making the counterhoops
So now we need to make the aluminium counterhoops that sit on the upper surface of the aluminium ring on the drumhead, they will be a greater diameter than the shell. But before you go cutting it to length you must bear in mind that 25 to 30cm will be wasted at either end of the hoop because of not being able to pass the whole length of bar through the bar bender. So clamp the bar bender in a vice, place the end of the bar over the two lower wheels, then tighten the adjusting bolt for the middle wheel so it just applies slight pressure on the bar. Now pull the entire length of the bar backwards and forwards, then tighten the bolt a bit more and keep repeating the process to curve the bar. Eventually you will need to remove the bar to check its curvature against the drumhead. When it's correct, trim the uncurved ends so the hoop fits the head perfectly. Now use a 5cm length of the waste to make a joining piece, reduce its width from 20 to 16mm. Drill a hole for the 5mm screws at either end of the hoop, not in the centre, do it 8mm from the top edge (with corresponding holes in the short joining piece) and countersink the inside of the hole so the 8mm hex screw will be flush with the hoop surface. Fix the hoop together using the joining piece and put thread locking solution on the M5 nuts. Next drill eight 5mm holes evenly spaced and countersunk on the inside, these are for the bolts, the holes should be 8mm from the top edge of the hoop. The reason for putting all fixings up slightly nearer the top edge of the hoop is to avoid any possible damage to the drum skin. All this is shown below.
Making the counterhoop bolts
This can be the tedious bit. From the 12mm bar cut sixteen 16mm lengths. These are best cut with a mechanical saw, I cut mine with a hacksaw and spent ages getting the ends to be straight and level. These now need to be drilled and tapped. If you do 16 of the design on the left of the picture, they are the easiest as the tension rod passes through the holes in the bolts on the top and bottom hoops and therefore each tension rod will have a nut at each end for tuning. However, when I made a repinique, I used the design on the right as it leaves no protruding tension rod above the top skin so you don't go damaging your hand when playing and you only need one nut on each tension rod for tuning. But for a surdo the first design is ok top and bottom. A vertical drill stand and a small vice is essential for acurate drilling. Afterwards, round off all edges with a file.
Making the tensioning rods
These are simple enough to require no pictures, you will need eight of them, threaded at each end. Some people like them longer at the bottom, so the drum can be played standing on the floor, others prefer them to be no higher than the drum head. Self locking nuts are best to retain the tuning.