A common question when planning wooden weapons like tonfa is what wood should it be made from. Being martial artists, we tend to go in one of two directions when thinking about weapons - strong and heavy or light and quick.
So, how hard does wood need to be to make a good weapon? If you're going to be making a lot of weapon to weapon contact, people tend to lean towards "as hard as possible". Exotic hardwoods can be very hard and very heavy. For reference it helps to compare to something familiar - the tried and true wooden baseball bat. Something you swing at a hard ball moving at 90 mph and it comes back for more.
Janka Hardness is commonly used to measure how hard a wood is. It is the average amount of force required to embed a 0.444" (11.28mm) steel ball half way into the wood. It is important to note that this is an average - no piece of wood is identical to the next so any individual piece may be harder or softer but averages are great for relative comparison. The chart below shows the hardness of woods commonly used in a trusty baseball bat. Hickory comes in at the hardest at just under 1900 pounds of force.
Janka Hardness (lbf)
Given the above information, anything over a Janka Hardness of 1200 should hold up to light contact training. The typical tonfa you can purchase from a vendor is made of oak. That said, I've broken several of those personally. Anything over 2000 hardness however - nearly twice as hard as the standard mass produced tonfa - should stand up to regular contact. The chart below shows some of the woods I've had the opportunity to work with.
Janka Hardness - Exotic Hardwoods
Redheart compares to Red Oak for hardness. It finishes smoother than Oak and has a good feel to it. I recommend it for competition and kata practice. It can hold up to light contact.
Pau Ferro is comparable to Hickory although it is slightly harder and heavier. It's a good choice for an all round weapon.
Purpleheart is harder and heavier than any of the previous woods, about 20% harder and only a bit heavier than the hardest of the wooden baseball bats. It takes a good beating - I've tested it personally. It's purple colour will change to a darker brown over time and UV light accelerates the color change.
The top end of that scale shows Cocobolo and Verawood. They are hard, heavy and take a beating like nothing else. They are also rare and expensive - the expense is in part due to the wood itself and in part to the abuse they cause on tools and blades. Of course if they wear down the metal tools used to shape them, they should stand up to other woods quite well.
I have a Cocobolo Jo, concrete scratched it once. That is all.