I was making a surround for a garden tub for my neighbor. He had gotten some Cumaru to use, an expensive exotic wood similar to Brazilian teak. Since it was such an expensive wood, I was very careful to make a template out of mdf to use as a guide to cut out the final product. I made the template to my satisfaction and traced it onto the glued up panel of Cumaru, then cut it out on the bandsaw just outside the line. I was using my flush trim router bit to trim it to the exact shape when the accident happened. From doing a little research on the wood after the incident, I learn that it's an extremely hard wood with interlocking grain that blunts tools very quickly. When I made my first pass around the template it left just a little rough place in one area; when I went back to smooth that area out the bit grabbed the grain, completely shredded the edge and leaped into my left hand that was holding the piece. I'm confident this wouldn't have happened using almost any other type of wood but it doesn't excuse the poor safety mistakes I made.
Lessons I hope I learned:
1. Never, ever get in a hurry running power tools. NO EXCEPTIONS!
2. If you're using an unfamiliar wood, research the characteristics of it.
3. ALWAYS clamp down your piece if you're using the router by hand.
4. ALWAYS use two hands on the router.
Below is some of the characteristics of Cumaru.
DENSITY AND BUOYANCY
Janka hardness is 3540, making it somewhat hard and durable, 174% harder than Red Oak (1210 Janka). Average weight is 71 lbs./cu. ft. Specific gravity is .86, making this wood dense and extremely hard.
DRYING AND SHRINKAGE
Very unstable when used in dry climates and it is prone to shrinkage. It is naturally seasoned and kiln dried to prevent shrinkage.
WORKABILITY
Being one of the hardest woods on the planet, the wood is difficult to saw and bore and will have a fairly high blunting effect on tools. Where severely interlocked grain is not present, the wood planes to a smooth surface. Because of its high density and oily nature, the wood glues poorly. It nails and screws well; pre-boring is necessary.
Charlie S
