I could never really get along with standard head torches, as you can only wear them on your head- that is, they're no good for holding in your hand. Its also near impossible to get a completely waterproof , powerful, head torch.
I just received an exceedingly nice head torch from Dealextreme, so went about using what I could find to get a sweet job done.
Step 1: Get Your Stuff Sorted
So we need:
A torch- I used a CREE 100lm waterproof diving torch. You could use a Maglite, a $2 shop torch, whatever.
An old head torch to pull apart. You could also use some elasticated material with a tightening buckle.
A small amount of Bicycle inner-tube.
Step 2: Sort the Old Headtorch Strap
Now, Pull apart the old headtorch strap. It was very simple to do this and just leave the one around-the-head strap, including the tightening buckle. You could leave the top-of-the-head strap on, and I debated this, but it holds fine with the one, and I don't like overcomplicating things for no reason.
Step 3: The Innertube
Now grab your innertube, and cut it to size. I made mine the length of the handle up to the switch, so I can use the switch easily, and take the head off the torch to get to the batteries without messing with anything. It holds the torch onto the strap very securely.
Now thread the innertube onto the strap with a little pokeying.
Step 4: Attach the Torch On
Now you pull the innertube over the torch. This was quite a squeeze with mine- the innertube was small and the torch is a fair size. This will probably remind you of ... sausage making... when your doing it. Attach the torch on halfway along the strap, so the buckle is on the other side of your head when wearing it and is easy to adjust.
You may have to use a different sized innertube (are there different circumference innertubes?) if your torch is smaller, or bigger. Mine came from an old racing bike if that makes any difference.
Step 5: Test It Out
Now you've gotta put the torch on your head, and cut the excess off the strap. I left a fair bit so I can wear a thick possum wool hat underneath, or let someone else with a bigger head use it.
Step 6: Job Done!
Now marvel at your headtorch torch. This torch is fairly heavy (4 AA batteries) and the single strap holds it fine. A siliconised strap would hold it even better.
I also cut another little band of innertube to hold the strap to the torch when stored of holding the torch. You can also use the strap to secure the torch to your hand, if your that way inclined.
I use the torch for everyday stuff, freediving, and rounding up the cows in the early morning!