Some of Goodwinds’ customers require extremely straight rods and tubes for their applications.  Perhaps their end products are precision tools used in physics labs or aeronautics.  Perhaps a super-straight rod helps their arrows fly true or the airplane stay in balance.

Getting straight pultruded carbon tubes is no mean feat.  Sure, every 48-inch length of carbon fiber tube might look straight to the naked eye, but might in fact deviate more than five hundredths of an inch over those 4 feet.  That minute deviation can be critical do the structure of a design.

We have a couple of different ways of testing our carbon tubes for straightness.  First, we can roll them along a straight, flat surface, like a slab of granite, and check for roll variance.  Though this is low-tech, it is quite effective.

Another method is to use our lazer micrometer to measure the deviation of the tube from the center.  The machine slowly spins the tube as a lazer passes over the center.  A computer interface generates a graph and, with a lot of math, a precise measurement of the deviation.  In this manner, we sort our tubes for straightness, setting aside those that deviate less than two hundredths of an inch over 48 inches in length.

There are inherent difficulties in created straight pultruded tubes.  During the manufacturing process, the carbon fibers are oriented and drawn through a die with a binding agent (usually epoxy or vinyl ester resin).  They are then pulled to a second and a third die, each time getting closer to the goal diameter.  As this is done over several feet, gravity and other forces can pull the carbon fibers to one side or another of the tube, causing it to lose a small degree of straightness.