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Grandpa Burnham was showing me the pink scar across his palm. "I can't work in the shop right now.
The doctors had to sort out the nerves in my hand." I was in high school in the 70's and Grandpa was
telling me about his carpal tunnel surgery. Unfortunately, a lot of woodworkers face the same health
problem today. It might result directly from our woodshop work, or it might be something we get from
other exposures that ends up aggravated by hobbies like woodworking. In college I studied industrial
ergonomics and then worked in factories to redesign jobs that hurt people. As I think of Grandpa
rubbing his palm and wanting to get back to his woodshop to finish up some projects, I wish I could have
shared some of these tips with him to avoid the pain and frustration he experienced.
Our hands are an incredible part of the body. Biomechanically there are 27 degrees of freedom
(different ways the hand can move) in the hand/wrist. Think what that means in woodworking - you
grasp tools, pick up boards, manipulate parts, open jars, point and poke and touch. A large part of your
woodworking skill comes from careful, precise, coordination of hand/wrist motions - broadly called
manual dexterity. Through repetition and practice of fine motor tasks, your brain develops efficient
neural pathways that enable dexterous performance. Woodworking is a craft that helps you develop
manual dexterity (dental schools like to see woodworking as a leisure activity on your application).
Figure 1. Marquetry uses many of the 27 degrees of freedom in your
hand/wrist for precise freehand cutting.
Part of your amazing hand is the sense of touch. There are two kinds of nerves to detect warm/cool and
four types of mechano-receptors to detect vibration and pressure. I love the name - Pacinian
corpuscle - that's one of the ones that detects vibration. When you touch something this complex web
of specialized sensors in your skin collects reams of data about how much and how fast and where. All
this information goes to your brain where more amazing stuff happens to sort out the data and generate
information about what you are touching. Close your eyes and touch that piece of wood in front of you.
Your brain is telling you something about warm/cool, rough/smooth, soft/hard, sticky/slippery. Studies
show that people can detect surface differences in the nanometer range (that's small) and we can
detect temperature differences of about 1 degree C. The apprentice hands the master a board and asks, "Is this
good enough?" A pass of the master's hand and the answer is back to the bench for more scraping.
Figure 2. Is that joint flush? Is the surface smooth?
Our nerves are more than just data collectors. They are wired into a feedback loop with nerve sensors in
our muscles and joints. When you pick up your marking knife you grip it lightly in a pinch grip. You know
how hard you need to squeeze, and you know how hard you are squeezing. Your brain, muscles, and
touch sensors are firing away in a coordinated dance to effortlessly glide the knife along the line. But
then you reach over to pick up a #7 bench plane and your handgrip immediately dials up to 10 lbs. The
touch sensors in the palm of your hand are now measuring how hard you are pushing the plane into the
wood and how hard the wood is pushing back. The adjustment from precise and delicate to firm and
strong is effortless.
But, to quote a certain band from the 70's, touch is, "more than a feeling." Close your eyes and pass
your hands over something soft like perhaps a Christmas sweater. You can easily describe the sensations
along the dimensions of smooth/rough, hard/soft, sticky/slippery, warm/cool. But your brain goes
further. It connects that neurophysical sensory input to emotional responses. Maybe memories of happy
times or family or just an inner sense of comfort. Warm-soft-fuzzy generally creates a favorable
emotional response. There is a whole line of research on how people emotionally react to the touch of
wood. This is important for product design - is a glossy varnished surface perceived as more
"pleasurable" than a plastic laminate surface? Is an open-grained wood like oak perceived as more
"natural" than something like maple sanded to 400 grit? The kinds of emotional descriptors that
researchers test include adjectives like, "thrilling", "uncomfortable", "irritating", and "calming".
Our hands are one of the most important ways we engage with the world around us. We touch, we feel,
we hold. We change the world when we put our hands on it and the world changes us through our
hands. The woodshop is a particularly potent smorgasbord of somatosensory (touch) delight. When
most of us step into a shop and see an old tool - we reach out and touch it. When we see a wooden
object made by another - we pick it up and touch it. Inspired, we pick up a board, grasp a tool, and
begin to create. If you could see all the sensory activity while you work, it would be a glorious lightning
storm coursing through your hands and head. But your brain sorts out all those exciting impulses and
simply says, "a little more to the left" and, "this is joy." Take a new look at your hands.
Things I Wish I Could Have Told Grandpa Burnham
Carpal Tunnel Syndrome (CTS) is a cumulative trauma disorder that results from various combinations of:
poor hand/wrist posture, hand/arm vibration, forceful grips, and repetitive activities. It is also influenced
by a host of personal factors such as body mass, hormonal levels, and age/gender. One of the challenges
in addressing CTS is that one person may suffer from it while a co-worker, using the same tools and
methods, never has a problem. The basic etiology of CTS is that something causes swelling in the
tendons that pass through the wrist (the carpal tunnel). Swelling pinches the nerves and you lose your
sense of touch. It becomes a self-driven cycle of inflammation, pain, pinching, more swelling. All that
said, there are a few key woodworking task factors to keep in mind to minimize your risk of CTS.
a) Never use your hand, particularly the palm of your hand, as a hammer. We all do this, thumping on a
misaligned board with the palm of our hand. This kind of impact can lead to inflammation and swelling
that may trigger the development of CTS.
b) Watch out for forceful grips. Objects that are slippery, handgrips that are too big or too small, things
you have to pick up by pinching instead of grasping - all these things tend to cause us to squeeze tighter,
putting more strain on the tendons of the hand. Gloves are a mixed solution. Some gloves may give you
better grip, but poorly fitting gloves can just make it harder to grasp things and make it worse.
c) Keep your wrist in a neutral posture as much as possible. The tendons passing through the tunnel
slide easier when they can just slip back and forth through the tendon sheaths. If they have to go around
a bend because your wrist is bent, that adds friction and strain. Neutral posture for your wrist is like a
handshake position - thumb up, palm pointing straight ahead. Think of a plane tote. Your neutral grip is
a "pistol-grip" with whatever you are holding onto (like a plane tote), at an angle of about 25-30 degrees
from the vertical.
Figure 3. Think about how the height of your work affects
keeping your wrist straight.
d) Minimize extended hand-arm vibration exposure. In my shop doing custom furniture, the biggest
vibration exposure comes from random orbit sanders. Other shops might use more pneumatic tools or
reciprocating tools that can also create other vibration issues. To minimize vibration exposure, limit your
time with the tool and try to have as loose of a grip as possible. There are special gloves that can help
buffer vibration if you have a serious job exposure.
e) Reduce exposure to highly repetitive gripping, twisting, and pinching. Grandpa Burnham made mini-
scrapers out of old hacksaw blades. When he was shaping the body of a violin he would repeatedly
pinch and push on those tiny blades. If you think about it, in the course of an hour, he was pinching
hundreds of times. Classic risk factor for CTS.
f) Be aware of your whole exposure. CTS is a cumulative trauma disorder. Your body doesn't know the
difference between work hours or recreation. If you work in your shop and then go play video games, or
spend hours typing on a computer, you will accumulate more stress and strain on your body.
g) Finally, listen to your body. If you have any nerve symptoms (tingling, numbness) or if you feel like
your hands are sore or tired after a stressful bout in the shop - take a break. Continuing until you can't
stand it any more isn't a good plan. There are non-surgical interventions to help break the cycle of
inflammation if you catch the injury early enough. Be kind to your hands, enjoy your shopwork!
Bhatta et al. 2017. Sensory and Emotional Perception of Wooden Surfaces through Fingertip Touch.
Front. Psychol., 13 March 2017 https://doi.org/10.3389/fpsyg.2017.00367
Sennett, R. 2008. The Hand, Chapter 5. In: The Craftsman. Yale University Press. 315 p.
Bob Rummer lives in Colorado and is a part-time woodworker. He can be reached directly via email at email@example.com. You can see his shop and some of his work at www.JRummerSons.com.
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