Fixing Mallets For Good
How to Repair African Marimba Mallets
So the Shafts Don’t Break
and the Heads Stay Tight

By Aaron Shepard

The Right Glue
The Right Wood
The Right Method
The Right Results

When I joined Mukana Marimba, the African marimba band I play with, I found the band members engaged in a continuous cycle of mallet repairs. Over and over, a mallet shaft would break, or a head would come loose. Then we’d repair the mallet and wait for the next time.

After a little thought and experiment, I found that these mishaps were almost totally avoidable. They occurred for the same reasons they occur in most other African marimba bands: We were using the wrong wood and the wrong glue.

The Right Glue

When you ask African marimba players about the best glue for mallets, they generally answer in terms of relative strength. You might hear about Gorilla Glue, for instance, or Shoe Goo, each among the strongest in their class of adhesives. But what you won’t hear, and should hear, is that these are the wrong kinds of glue entirely.

Though there are many kinds of glue, they fall into two basic families. The first is evaporative. These are glues that include a solvent, either water or a hydrocarbon. They attain their strength as the solvent evaporates. The important point here in terms of mallet heads is that evaporative glues shrink as they harden. They lose volume as solvent leaves them.

This property makes them well suited to flat surfaces. If you apply carpenter’s glue between two flat boards, for instance, the glue will actually pull the boards together as it dries. If the boards are properly clamped, the result is a bond that is stronger than the surrounding wood.

But the situation is different with a mallet head. Here you have a rod (the wooden shaft) inserted into a hole. If you use an evaporative glue on this joint, it can’t pull the surfaces together. Instead, it shrinks, leaving gaps as it dries, or at least reducing the pressure between the surfaces. The resulting bond is necessarily less than full strength, because the shrinkage weakens it.

This disadvantage is made much worse by what is supposed to be a solution to it. To keep the head from flying off, it’s common to leave a ridge at the end of the shaft and to reduce the shaft’s diameter behind it, where the head will sit. This means the hole in the head has to be extra wide to fit over the ridge, guaranteeing the poorest possible bond to the narrower part of the shaft.

The real solution to this problem is to use an expansive glue. These are glues that you set by mixing a resin and a hardener, the most common such glue being epoxy. The functional difference in this type of glue is that it expands as it hardens. This makes it ideal for our rod in a hole, because the expansion strengthens the bond.

If you want to see the difference that an expansive glue can make, pull the head off a mallet with a battery cable puller—a corkscrew-like mechanism available at any car parts store. With any of the glues commonly used, it will pull off with little trouble. Now glue that head to a shaft with epoxy and try the cable puller again. You might break the head, but you won’t get it off the shaft!

The Right Wood

The one problem with using epoxy on mallet heads as that the head is on there for good. There really is no way to pull it off. Your only recourse is to drill out the shaft. Obviously, you want to avoid that difficulty if possible. And that’s why it’s so important to make your shaft from wood that won’t break.

What wood might that be? Well, it’s not the common, birch dowel you pick up in your hardware store, as you no doubt already know. What about dowel from other hardwoods? Some may be more likely to avoid breakage, but most hardwoods are too heavy for shafts. You want something as light as it is strong.

The answer is hickory. It’s light and strong enough that it’s the wood of choice for the handles of hammers, axes, and other hand tools. It’s also used for drumsticks. (And yes, those do break, but they get a lot more stress than marimba mallets do.)

You probably won’t find hickory dowel anywhere local, but you can get it on the Web. My own U.S. source is Midwest Dowel Works at www.midwestdowel.com.

The Right Method

So, now we have the right glue and the right wood. What’s the right way to put them together?

For soprano and tenor mallets, I buy half-inch-thick hickory dowel in three-foot lengths, then cut the shafts just 1 foot long to get the most pieces with no wastage. I use a hacksaw with a metal-cutting blade and a mitre box to minimize splintering.

With rough sandpaper, I smooth the ends of the shafts and round the edges. This is important at the holding end for comfort, and at the head end to help the shaft enter the hole. I leave the rest of the shaft unsanded so it will be less slippery for playing.

If your mallet head is still on a broken shaft, pull the head off with a battery cable puller. Ideally, the hole in the head should be a bit smaller than the new shaft—maybe 7/16 inch for the half-inch dowel. If the hole is as wide as the dowel, your bond won’t be as strong because you’ll get no clamping action from squeezing. If the hole is smaller than 7/16 inch, you risk breaking apart the head when you drive in the shaft, if you can get it in at all. (Unfortunately, there’s no easy way to enlarge such a hole. About the best I can figure is to glue in a smaller shaft and then drill it out with a larger bit—if it’s worth the trouble.)

I use regular, 24-hour epoxy, because it’s stronger than the five-minute kind. After mixing it, I use a flat toothpick to liberally coat the inside of the hole. That’s where it goes—in the hole, not just on the shaft. You can put it on the shaft too if you like, but most of that glue will be squeezed off at the entrance to the hole anyway—and if you apply glue only to the shaft, there may not be enough left on it when it reaches the far end. With the glue applied in the hole itself, you’ll get good coverage all the way through.

Remember, you want as much epoxy in the joint as possible, because greater volume strengthens the bond. That means you apply more glue than will ultimately fit in the joint. This is different than with an evaporative glue, which works best in a thinner layer.

For lubrication, put a little epoxy at least on the rounded edge at one end of the shaft. Now, place the lubricated end at the mouth of the hole and push through. If the fit is too tight to do this easily—which it should be, for the best bond—you can drive in the shaft with a woodworker’s mallet, or a hammer if you place something in between to protect the wood. You want the inserted end of the shaft to reach the bottom of the hole, and that’s all—in other words, the shaft end should be level with the top of the head, not sticking out.

You’ll now have a very messy mallet head, since the excess epoxy will have been forced out of the hole. Clean up with a paper towel soaked with denatured alcohol. Pay special attention to the striking area, around the rim. Then simply set the mallet aside and let the glue harden for a day or two.

The Right Results

So far, the outcome of my experiment has been just as hoped. After several months of playing, Mukana Marimba has failed to break one of these shafts or to loosen one of these heads—and some of us tend to be hard on mallets!

Let me know if my approach works as well for you. I’ll post reports here.

Mar. 22, 2008—Revised Mar. 24, 2008