Advice and questions on making and fixing instruments
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By Rhythm House Drums
#10847
I get asked a lot about how I make my staved ashikos and what is important that effects quality and sound... I recently answered one (fairly lengthily) and thought maybe I can post it here for anyone that's interested in building one themselves...

I wont post his e-mail to me.. but below is my answer which hit on most all of his questions... The formula he's talking about was found online somewhere... and not quite correct.
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Take the formula with a grain of salt ... It’s missing a crucial angle for ashiko (or any tapered drum). That formula works great for a barrel drum like the dununs, but there becomes an issue the more you taper it. Some hobby drum builders ignore this calculation, and will even argue that it doesn’t exist... Maybe to protect their drum making ability?? The fact is, it does exist, and if you want your angles to line up perfect you have to pay attention to it. Think if you have 18 staves, and you are 1/18 of a degree off on your angle... Because you angle both sides of the stave.. That means your final stave will end up 2 degrees off. Your shell might still glue up, because it will spread that out over each stave, but it will be prone to cracking and over time it’s going to break at one of the joints. 1/18 of a degree is really small... You need a tool that will measure your angles very accurate. Using 18 staves your formula will give you 10 degree angle on each side (good for a barrel drum (same diameter head on each end)... I suggest start here... However with the taper of a standard ashiko your actually angle will be about 9.8 degrees... Like I said, some ignore this angle. There was an article online I found that explained it well (whish I found it before I went through the trouble of collaborating with a math professor...) http://www.drbobsh.net/drum_calculations.htm

It’s confusing, but it is valid... Especially if you’re a perfectionist and want your drum to come out just right. Other things to be aware of is to make sure you plane your staves down before you bevel them. This makes them consistent and each face parallel. (which is important for that bevel angle)... I’d say between 1/2” and 5/8” is thick enough. Much thicker and you wont want to carry your drum around with you. Make sure each stave is exactly the same size...

I will do a fake glue up before I do the actual one... Just to make sure everything comes together right...if you glue it up and something got off... You end up with a bunch of scrap wood, if you make sure it will be round before you glue, you can save some wood.. And make minor changes if needed.

A normal taper in the ashiko will make you loose about 1/4” in height. (a 24” stave will give you an ashiko that stands 23 3/4” tall) Depends on the taper, but that’s about how mine come out.

If you are doing a drum 14 or 15 inches in diameter... I’d suggest using 22-24 staves. The more staves you have the more round your drum will be, and the more consistent the wall thickness will be once you round it. A drum that big may not give you the sound you want... Just depends on what you are after. I would recommend 14” at the most.. And with it that big, probably head it with cowhide.

The diameter of the head to the sound hole to the cubic feet of space inside the drum will all vary the sound of your drum... I wouldn’t worry about this too much. Unless you have studiofile ears and are after a specific sound... There are so many other factors more important for the new drum builder (like skin thickness & type, wood, heading style, and the bearing edge) A good starting point is this ratio (body length:head:sound hole) (5:2:1) (so... 25” tall 10” head, 5” base) (inside diameter for those... Outside diameter if your wood is 1/2” thick will be an inch larger.

Most ashikos are between 10 and 12.5” Because of the shape, this rang gives the best sound.

A larger diameter head can be deeper in pitch but is louder (head size = volume) length of the drum will hold the resonance and the sound how will determine how fast the sound leaves. The skin thickness will have a LOT to do with the way the final drum sounds. If you look at speaker box calculations, you’ll notice that that they account for the inside area as well as the range of motion of the speaker unit you use in it do determine the size of the port... In our case the range of movement is determined by the thickness and tightness of the skin.

I’ve not read Hopkins book.. Maybe I should take a look at it. Just think about PVC pipe... If you hit the ends of the pipes, the longer ones will be deeper because the sound waves travel further.

Inside smoothness of the shell doesn’t matter at all... Actually sometimes I’ll roughen up the inside of a shell if it rings too much. For a large bassy drum... I’d rough it up. It will make the drum smoother (in sound). The rough wood will absorb more of the high end ringing... Super slick surface is allow the waves to bounce around and you’ll hear lots of overtones.

The bearing edge is crucial to sound... It has to be level and the round over has to be even... Should be easy on a lathe, but you might also want to try a round-over bit on a router with bearing guide.

Can’t help you with the shell on the lathe, I don’t use one. I use a hand plane to get the shell as round as I can, and finish it up with a belt sander before I sand down... A lathe is a good option, I just don’t have one! :)

Turning the drum wont make improvements in the sound.... A perfect bearing edge will (which is easier to get if the shell is perfectly round...like from turning it on a lathe).

Wow this is way more that I was going to write....

Final note... Whatever you do... DO NOT use the cinch tuning (or the other I’ve seen is little plastic pieces that you use to twist the verticals). It’s crap, it’s a gimmick that manufactures that make cheap drums try to use to sell their drums.... It’s much less expensive to do and easy to do... It wont keep your drum in tune, you’ll never be able to get it tuned properly. Use the Mali weave. Tried and true... It works! On that note... Its a good idea to make a bottom groove on the drum for the bottom ring. This way you can make sure it stays level and it wont ride up the drum over time as you tighten the verticals.... Since you have a lathe this should be super quick (not so quick for me... hand saw/chisel)

Hope this gets you started. :) (off to finishing up some bearing edges for a set of dununs)
User avatar
By michi
#10852
Wow, nice work! I'm sure that people who are planning to build a staved drum will truly appreciate this!

From reading the calculations and description, without a proper bench-top planer and a serious mitre saw, there is no way to cut those staves and have them work out. I guess the main lesson for me here is that it's another reason to buy shells that are carved out of solid piece of wood :) I don't think I'd want to put myself through the work of building a staved drum...

Cheers,

Michi.
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By Rhythm House Drums
#10857
Actually my first ever ashiko was built completely out of poplar wood on a 100 dollar table saw from lowes hardware.. :) I used some goopy glue mess... it was all odd shaped, but the angle was close enough to glue it up. (It was sacrificed to the fire gods some time ago)

Congas... wow.. I've tried to wrap my head around that, I know they are steam bent but that conga curve on each stave has to be just right, and the bend has to be perfect on each stave. A CNC router could take care of the curve and bevel angle. I've seen a jig that you can put the staves in after they are steamed that will bend them all at the same time.... it's more than I want to get into though!

I know ahsikos... that's what I'll stick to!!
michi wrote:I guess the main lesson for me here is that it's another reason to buy shells that are carved out of solid piece of wood :)
Or a staved shell from Rhythm House Drums!! :dance:
#38967
This was an interesting thread and an insight into stave drum design to some degree.

Paul asked for the write up from dr bob sh , the link which rhythm house provided, and here it is. Unfortunately the diagrams are not present. I just searched for a cached version of the site and found this. Complicated enough anyways and interesting too.


When building a stave type ashiko, usually 12 or more staves are cut separately using a table saw, then glued together to form a cone as illustrated at left. Calculating all the proper angles can be difficult, and requires some fairly extensive geometric equations. There is a wonderful program called DrumCalc that calculates most of the angles for you. There is one angle that DrumCalc doesn’t give you, and this page tries to show what that angle is, why it is important, and how to calculate it.











The basic angle used to cut the staves is noted at left as Theta. This angle is simply 360/N where N is the number of staves.





















When the staves are cut on the table saw, the blade must be set at an angle. Since the staves are laid flat when cut, the angle to use is not Theta, but Theta’. Theta’ is formed by drawing a line from the middle of the top of the drum to the stave such that it is perpendicular to the stave, as above. And Theta is not quite the same as Theta’. The more angled the stave is, the more the difference between the 2 angles. The difference is small for most ashikos, but when the same calculation is used for the bell of a djembe, the correct angle is critical. If you don’t make the correction, your staves will not fit together tightly.



Here the 2 angles are shown together, on a stave that I have made short and with a steep angle to better accentuate the differences. Note that this stave is pretty close to what you might use for a djembe bell, though.

















Here I have labeled all the important vertices so that I can refer to them for the calculations. I am also going to use the following notation:



L1 = BC = stave top outside dimension

L2 = DE = stave bottom outside dimension

L3 = FG = stave width at the perpendicular




AB = R1 = top drum radius (see notes on this below) HD = R2 = bottom drum radius

AF = R3 = radius of perpendicular BD = V = outside length of stave

AH = DK = h = drum height N = number of staves

For the purposes of the calculations, all angles will be in radians.

Using simple geometry:

θ = 2π / N ;

L1 = 2 * R1 * sin (θ / 2) ;

L2 = 2 * R2 * sin (θ / 2).

Using similar logic, we can say

L3 = 2 * R3 * sin (θ’ / 2)

The triangles AFB and EKB are similar. Therefore:

AF / AB = DK / BD , or R3 / R1 = h / V ; therefore R3 = R1 * h / V

where V can be calculated as:

V = Sqrt ( h2 + BK2 ) ; where BK = R1 – R2

if we define x = BF = the distance from the top to the perpendicular, we can similarly note:

x / R1 = (R1 – R2) / V

Since the sides of the stave are all straight:

L3 = L1 – (L1 – L2) * (x / V)

We now have calculated L3 and R3 in terms that are known, and using the formula above, we can calculate θ’ as:

θ’ = 2 * sin -1 ( ˝ * L3 / R3)

The closed form is lengthy and I don’t think it is worth trying to type it all out here. Using the formulas above, it is easy to set up a spreadsheet to calculate all the parameters. The link below is to an Excel file that does just that, for those who have access to Microsoft Excel. I am not enough of a programmer to be able to put together a Java program or something as neat as DrumCalc that does it all by itself.

<----- Click on this to download the Excel file.

Below is a sample calculation using some parameters from a drum I am currently making. Note that there is about a 4.5% difference between θ and θ'.

Ashiko calulations for stave drums
ENTER DATA HERE
14 Top diameter
6 Bottom diameter
13 Height
34 # staves
R1 7.029989 Top outside dim 14.05998 Top peak to peak diameter
R2 3.012852 Bottom outside dim 6.025705 Bottom peak to peak diameter
H 13 Height
N 34 # staves
R1-R2 4.017136
V 13.60652 Outside linear stave straight length
x 2.075507 Linear straight length to perpendicular
R3 6.716622 Radius to perpendicular
l1 1.297291 Top stave outside dimension
l2 0.555982 Bottom stave outside dimension
l3 1.184213 Width at perpendicular
Th1 10.58824 5.294118 Stave angle
Th2 10.115 5.057499 Corrected stave angle
-0.23662 Difference
-4.47% % difference
NOTES
Diameter is measured across from flat part to flat part
Diameter from peak to peak is calculated in column E above
A note on the difference between the flat to flat vs. the peak to peak diameter. If you have a lot of staves, they are close to the same, but if you have only a few, there can be a lot of difference. The relationship between these two is:

R' = R cos (θ / 2)

where R' is the flat to flat and R is the peak to peak. The diagram below shows this relationship graphically. Here

AB = R ; AJ = R'
By the kid
#38970
The images don,t show up as the info is from a cached version of the web site which is no longer available. so we need a reverse engineer to fix that problem.

RHD gave some good insight into stave building. Must be tough to actually construct a djembe.

But duns much easier.