Intro: Build a Compact Propane Tank Tongue Drum
First of all I need to give credit where credit is due. The original hank drum is the creation of Dennis Havlena. Dennis is an awesome guy- he had a good idea and instead of starting a company, he started a movement. He shared his design freely and enabled a lot of folks to explore their creativity and make a little money if they choose.
I also owe a debt of gratitude to Bart Hopkin for his book Musical Instrument Design. It's the go-to guide for anyone interested in making their own instruments.
So what's so different about this propane tank drum? There are already several designs floating around out there, like this one from Hermes or this one from -Moon (which isn't actually made from a propane tank, but it's an awesome example of the type of instrument I'll be making). Most of the tongue drums I've seen have the tongues cut in a way that they are attached near the outside of the top of the drum. This helps isolate the individual notes, as the sound waves are stopped somewhat by the bend in the metal at the edge. My drum is cut the other way around- the tongues are connected to the drum in the center of the top in an arrangement that resembles a flower. This does two things- it allows for sympathetic vibration in other tongues to create harmonics and more sustain and it allows for more tongues to be used. My drum has 7-11 different notes in a pentatonic blues scale. My drum is also cut down to an interesting UFO shape to make it a bit more portable and comfortable to play.
I've tried to limit this project to use common simple tools. I'll give plenty of suggestions for alternatives, so you shouldn't have much trouble making your own. Specialty tools just make it a quicker job.
Step 1: Preparing the Tank
This drum is made from a discarded propane tank. I buy tanks from the local welding supply shop as scrap metal. Tanks have to be hydro-statically tested periodically. If a tank is found to be unsafe or to have too much rust and pitting, it is unfit for use. They drain the residual propane and remove the valves. When I buy scrap tanks, the first thing I do is fill them up with soapy water and let them sit overnight. This insures that there is no residual gas left in the tank and it reduces the sulfur smell from the gas adulterants.
After the tank is drained, rinsed and dried I can process it to make a drum. The first step is to remove the ring from the bottom and the handle from the top. The bottom ring is welded to the tank in three spots to create a stable base to sit on. It can be removed by gripping it with a pair of vice grips next to a weld and rocking the metal back and forth until it breaks. I did this for each weld to free the ring. This left some lumpy metal on the surface. I used an angle grinder to remove the rest of the weld and make the metal smooth.
I flipped the tank over so that the handle was on top. The handle was welded in such a way that it could be easily cut with the angle grinder. I cut it off and left the residual metal intact until the next step.
Step 2: Spinning and Grinding
I built this custom stand a few years ago. It used to be a big steel frame that held marine voltage inverters while they were being repaired. I got it from a shop that was going out of business. I decided to make it into a custom drum building jig. It allows a propane tank to be threaded onto a nipple and spun along its axis. It can also be locked in place with a pair of vice grips. This jig allows the tank to be spun while it's ground with the angle grinder. The spinning wheel of the grinder can be tilted to control the speed that the tank spins at. This removes all the paint from the tank and leaves a cool swirl pattern in the metal's surface.
Warning!!!- I've been doing this for a long time. Using an angle grinder on a work piece that is also spinning at a high speed is incredibly dangerous and probably actually stupid. Don't do it this way unless you are absolutely sure of what you are doing.
The drum stand isn't necessary, it just makes it easier to work with.
After grinding the 'bottom' of the tank I locked down the axle and ground the excess weld bead off of the top of the tank where the handle was. When the welds were ground smooth I spun the tank and ground the top to remove all the paint.
If you don't have a custom drum building jig laying around (What- you don't? What kind of monster are you?) you can always use a drill mounted wire wheel or even sandpaper to remove the paint. you can also leave the paint on the tank and paint over it later, although this affects the sound a bit. I want a drum with a metal finish so I removed all the paint from the ends of the tank. I'll be cutting the ends off, discarding the middle piece and reattaching the ends into a UFO shape so I didn't remove the paint from the middle section. We'll use it for something else later on- there's always a use for scrap metal around my shop.
Step 3: Marking the Tongues
I made this template a few years ago. It's based on some stuff I learned from Bart Hopkin's book. The numbered tongues 1-8 are tuned to a blues scale and I, II and III are the bass notes. In the key of C, 1-8 would be C, D#, F, G, A# C, D# and F and I, II and III would be C, F and G an octave lower than tongue 1. Also, these can be tuned as bass resonators that vibrate sympathetically with the smaller tongues. It's a bit trickier to tune, but it sounds really cool. To transpose the key you just have to make the tongues shorter or longer. We'll cover that later when we tune the drum.
The template has a hole in it's center. This is used to align the template with the center of the swirl pattern on the top of the tank. When the template was aligned and centered I taped it down firmly and traced each tongue. I labeled each tongue with its corresponding number to avoid confusion later.
The tongue marked 'I' has a 1" square marked so you can print it out and make your own template if you want. It's too big to do as a single print so you'll have to do multiples and paste them together. The easiest thing would be to use a digital projector to project it to the right size and trace it on a single sheet of poster board.
Step 4: Cutting the Tongues
Before the tongues can be cut I needed to make plunge cut for each side of each tongue. I used my Gesswein jeweler's drill motor. It's like a Dremel tool with a flexible shaft on steroids. I used heavy duty cut-off wheels and made two cuts on each tongue. This allows the jig saw blade to slide in and complete the cut.
When all the plunge cuts where done I used a jig saw to complete the initial tongue cuts. I modified the jigsaw blade by grinding the back side of the blade at an angle. This allows the blade to cut a tighter radius without too much friction. It reduces the life of the blade a bit as less metal means less heat dissipation, but it's a good trade-off. I inserted the jigsaw and cut each tongue towards the point where the cuts meet. I do this cut first. If I do it last the blade tends to bind when it finally breaks through and it bends the tongue. After the points were cut I cut each tongue in the other direction. I cut until just past the curve where the cut starts to straighten out. I'll cut them the rest of the way when it's time to tune the drum.
Step 5: Pre-tuning the Drum
There are many factors in play to determine the sound produced by the tongue. Think of a xylophone. Each piece is a different width and length, and sometimes even the thickness varies. Each tongue on my template is a different size to handle the general width to length ratio. I've cut the tongues just enough to clear the curves with enough room to insert a hacksaw blade.
To begin pre-tuning the drum I started with tongue number 8, the highest pitch on the instrument. The bigger the tongue the more it will vibrate. This means that the smallest, highest pitched tongues will ring less than the bigger, lower ones. I start with the highest tongue because it's the most finicky- if I can get it to ring, the rest will be easy.
As I said before, there are many factors that affect the way the metal vibrates and what sound it makes. There is no set length dimension for the tongues because thickness, degree of pitting and metal composition all have an affect.
I started by making gradual cuts on each side of the tongue with a hacksaw blade. I continued to cut, making the tongue longer, until it made a sustained ringing sound when I struck it. I used a guitar tuner to see what note it was producing and made a note of it.
This drum tunes to a pentatonic blues scale. If it was tuned to the key of C, the 8 smaller tongues would be C, D#, F, G, A#, C, D#, F. Now I have a choice to make. The three bass tongues can be tuned to C, F and G for a nice bass accent. They could also be cut long as resonators. Resonators are not 'played'. They vibrate at sympathetic frequencies to enhance the resonance and harmonic richness of the smaller tongues. Tuning resonators is a bit trickier than simply tuning three bass notes, but it makes for a really nice sound. I decided to tune these bass tongues as resonators, but for now I just tuned them as if they were bass notes. There are at least two more tunings, so we'll address the resonators later.
In this case the smallest tongue just started ringing at around F#, so a few cuts brought it down close to F. I worked backwards tuning each tongue close to it's note value in the key of C. As the lower pitched tongues got bigger they began to cause sympathetic vibrations in the other tongues. All this harmonic noise can make reading the pitch of an individual tongue kind of tricky. I use bamboo skewers sharpened like a wedge to dampen tongues I'm not currently tuning to make it easier. When it was kind of close to the scale and pitch I wanted I went back and retuned it even lower to G. By tuning it in steps things don't get out of hand and any problems become evident before they become disasters.
This is only the first tuning so it doesn't have to be precise. The main goal is to get the tongues into a proportional layout. This will make later tuning much easier. It's best to to the brunt of the tuning while the whole tank is still intact as it has a large resonant cavity making it louder.
When the drum is brought to a reasonable facsimile of the key of G it's time to cut the ends off.
Step 6: Cutting Out the Middle, Man
I put the drum back in the rotating jig. I used a separate stand to steady my marker and I gently rotated the tank to draw the cut line for the top of the drum. A long strip of poster board or card stock can be used to trace these lines as well. The idea is to cut the middle out of the tank and reconnect the two ends in a UFO shape. It's important that the bottom of the drum fits inside the top properly. If it's too smell it may interfere with the tongues and if it's too big the two parts will be hard to align.I traced out the cut line for the bottom of the drum.
I locked the axle with a pair of Vice grips and used an angle grinder to cut off the top of the drum. I set it aside and then cut the line to separate the bottom. I held the top up to the bottom to insure a good fit.
Step 7: Back to the Grind
Now that the tank has been cut open, the first order of business is to remove all the rust from the inside. I used a 4" wire wheel in a drill to brush away all the rust in the bottom and top parts of the drum. I also used the wire wheel to remove the remaining paint from around the valve hole on the bottom piece. I screwed two hard drive magnets to the tabletop to hold the parts in place while I removed the rust.
Since I'll be making the bass notes resonators I need to grind them to make them thinner. I put a screw between the hard drive magnets so that when the top of the drum was stuck down the screw head would make the one of the bass tongues stick up a bit. I used the grinder to carefully remove metal and make the tongue a bit thinner and more concave. This thinner metal will vibrate more easily when the smaller tongues are struck, causing really nice harmonics and adding 'depth' to the sound.
Step 8: Getting in Tune
Next I tuned the drum close to its final tuning. I want a drum in the key of E, so I carefully lengthened each cut. Since the final polishing and heat treating will affect the pitch and timbre of the drum I tuned it to the key of F. When the drum is assembled and polished I'll drop it a bit to E. I placed the top piece of the drum on a folded towel and made slight adjustments until it was tuned. I tune my drums in steps- lowering each note gradually in turn rather than tuning each tongue and moving on to the next. Go slow and be cautious- it's a lot easier to lower the note than it is to raise it back up. If you do make a mistake and make a note too low you have two options- if it's not too low you can flip the drum over and carefully grind some metal from the underside of the tongue's tip (this is why I tune it before I connect the top and bottom). If you lower a note too much you can always just lower the rest of the notes and tune the drum to a lower key. Tuning any instrument is an art- be patient and take a break if it gets frustrating.
When it's in tune, Use a wire wheel to remove any loose metal or burrs from the underside of the drum top. It may cause buzzing and will be really hard to remove later when the two halves of the drum are joined.
Step 9: The Heat Is On
Grinding, cutting and working the metal builds up heat and affects the way the metal vibrates. Caribbean steel drums rely on the tension created by having soft spots and hard spots in the same piece of curved metal. This makes them one of the most complex percussion instruments ever, from an engineering and metallurgical perspective. For our tongue drum we just want to heat it enough to bring it to a uniform hardness again.
I simply put the two drum halves into the oven at 500 degrees for an hour. I turned the oven off and left the door closed so the pieces would cool slowly for a couple of hours and then I repeated the process. This changed the color of the steel slightly and has a noticable affect on the timber of the notes.
Usually, I weld my drums. I would wait to heat treat them until after the welding, as that adds heat also. In order to make this drum a bit easier for folks to copy I'll be using J B Weld adhesive to connect the two sides of the drum. Since I'm not sure how it would handle the heat I decided to heat treat this drum before attaching the two sides.
Step 10: Sticky Situation
After the heat treating when the parts cooled down It was time to attach the two sides. I put the two pieces together to see where they touched and then used sand paper to clean up the mating surfaces. I gave them a wipe with an alcohol soaked rag and let them dry completely.
I added some pieces of tape to prevent the two pieces of the drum from shifting as I glued them. I mixed up some J B Weld and made a tiny spatula from an old gift card to spread it into the gap where the pieces came together. I worked the adhesive into the groove all the way around the drum and left it overnight to cure.
Step 11: Grinding Groundhog Day
I know you missed all the grinding from earlier so here's more. After the adhesive cured I returned the drum to the drum stand. I used the angle grinder to clean up the overlapping top edge. I also went around the edge of the adhesive on the bottom piece to remove any excess. I used my Gesswein jewelers drill with a grinding wheel to clean up and slightly bevel the edges of the tongues to remove any sharp or rough edges. I went between the tongue cuts with coarse sandpaper to remove any burrs then I went over the whole drum with the 4" wire wheel to buff it up and give it a more uniform finish. I like rough looking drums, like they've been carried through some post-apocalyptic waste land, so I'm not too concerned with making it perfectly smooth.
Step 12: Turn Your Damper Down
The drum is starting to sound pretty good, but it's a bit too 'ringy'. I built a damper to remedy that and bring the reverberation under control. I used a reducer that fit the 3/4" thread of the valve hole. It had a 1/2" threaded hole in its center. I used a scrap of 1/2" CPVC pipe for the damper arm. I screwed the reducer into the drum and stuck the pipe into it until it touched the top of the drum and marked it. I cut it to the mark. I made a sleeve by cutting an end cap in half and glued it onto the pipe. I taped a rubber ball to the end of the pipe (there is no glue that really works to attach these balls to anything) and screwed it into the valve hole until the ball was pressed firmly against the underside of the drum top in the center. This reduces some of the vibration and makes the individual notes a bit more distinct. You can adjust the tension for more or less ring as you see fit.
Step 13: Final Tuning
After grinding the edges of the tongues, heat treating the drum and connecting the two sides it was time to fine-tune it. I checked it with the tuner and all the notes were about a quarter step too high for the key of E. I carefully cut the tongues with a hacksaw blade until I had the notes E, G, A, B, D, E, G and A on the small tongues.
Ahh, the bass tongues. Honestly, tuning them to E, A and B one octave below the smaller tongues is much easier. If this is your first time building a tuned instrument, that would be your best bet. To create bass resonators I started by cutting them until they were about two octaves lower than the smaller tongues. At these lower frequencies it's harder to differentiate the primary pitch from the harmonics and overtones and the tuner becomes less useful. The resonators are best tuned by ear by hitting the smaller tongues and hearing the effect they have on the bass resonators. The smaller tongues will interact with the harmonics of the bass tongues and will often produce sympathetic vibrations that are different from the note they create when they are struck. Don't go by the numbers- go with what sounds good. There's a lot of leeway, and even 'badly' tuned resonators will give you some interesting overtones. If it sounds too cacophonous you can always tighten down the damper or add tape to the resonators until it's under control. Have fun and experiment.
Step 14: Finishing
When the drum was tuned it was time to finish it to prevent rust. First, everything got a good wipe-down with alcohol to remove any grease and grime. I used some Tempo Marine engine paint to coat the bottom of the drum. This is a tough finish that will stand up to abrasion and wear. Next I misted the top of the drum with Rustoleum black paint and buffed it off with a rag. This leaves paint in all the scratches, pits and grooves for an aged look. It also highlights the edges of the tongues. I let that dry and then sprayed it with a heavy coat of Sculpt Nouveau Bronze patina stain. I let this dry for a few minutes and then wiped it off lightly with a solvent soaked rag. This left patches of pigment and more aging in the low spots. I let it dry again and then added a light coat of the bronze patina stain. I topped it with a thin coat of a matte clear coat to protect it.
When adding any finish to the top of the drum it's very important to go as light as possible. Too much built-up paint will dull the sound of the drum. There are other alternatives for finishing a drum. I've rubbed wax on bare metal and even sprayed them with furniture wax. They can be spray painted or 'pickled' with chemical treatments. One of my favorites was wire brushed, allowed to rust a bit and then treated with phosphoric acid and sealed with varnish. It looks charred and ancient. Get creative with finishes and see what you can come up with.
Step 15: Final Notes
Here's the finished drum- give it a listen-
I use simple DIY mallets to play the drum, but it can also be played with your bare hands. My malets are amde from a short length of dowel with a vinyl cap (from Rubbermaid- they're end caps for their line of white vinyl coated wire shelving) on one end. The other end had a rubber ball with a hole drilled in it glued on. As I said before, there's no good glue that I've found for these balls, so I dipped them in Performix Plastidip rubberized coating a couple of times. this gives the mallet a long lasting surface and secures the ball on the dowel.
This is the first drum that I've glued rather than welded. I'm impressed. The main reason I bought a welder was to make these drums- I could have just bought a few cases of J B Weld! This is also the first time I've used this damper design. I like it and will continue to use it.
Don't get too bogged down in tuning. This is a folk instrument. It's designed for jamming on the sidewalk or around a campfire, not writing symphonies. Get it as close as you possibly can then go have fun with it and make the next one better. Learn from your mistakes and experiments. These are fun drums with a lot of room for modifications and innovations.This drum doesn't like hard surfaces. In order to resonate properly, it should be on a soft surface. Laps are the best, but you can set it on a pillow or rolled towel if you want to play it on a tabletop.
I play with the drum sitting flat in my lap supported by my thighs. I put the resonator tongues closest to me with the small tongues arranged away from me. An ascending scale can be played with alternating left/right strokes and vice versa. Since this instrument is tuned to a scale already there are no wrong notes. If you're playing with another instrumentalist, as long as they play in the same key your drum is tuned to it will sound great.
Of course you're not limited to just a pentatonic blues scale. My template is based on the ratios of the root note's frequency. Figure out the notes of your desired scale, google a note and frequency chart and come up with your own tuning.
Have fun and make some racket!