I recently purchased a Ryobi nine-inch electric pole saw for trimming tree branches -- for a cool $89 plus tax. After years of either using a manual pole saw or a gasoline-powered chain saw, Ryobi probably didn't have a more satisfied customer than me. In only minutes, I had a lawn strewn with pruned vegetation. I was so happy, I was extolling the virtues of this new tool to anyone who would listen. A co-worker even bought the exact same model after hearing my glowing review.
My happiness was dulled before the chain needed its first sharpening. During my last monthly cut fest, the motor/saw head started popping out of the pole during use, leaving the motor and blade hanging from the umbilical power cord, which is internal to the pole. After the third time, I was starting to think something was wrong.
It turns out the clamping collet base was coming loose from the pole. The pole telescopes at both the saw and handle ends, so the middle part is a plastic extruded pole with an oval cross-section, sawn and drilled at both ends. The clamping collets are made from two molded plastic parts. One screws for tightening on the telescoping rods, while the other acts as an adapter to the extruded pole.
To simplify assembly, the collet base part has opposing leaf springs molded in with internally facing little circular nubs that pop into the mating drill holes on long pole. The designer probably intended for the pieces to snap together and never come out, eliminating screw fasteners. Each time the pole and collet base popped apart, material was gouged from the periphery of the drilled hole in the pole, creating a nice little ramp, which made it even easier to pop out the next time.
It is quite possible I abused the joint with overstress during the time or two I cut the branch from the wrong side and the weight of the branch pinched the chainsaw bar. This required a bit of wriggling down below. That movement could have easily exceeded the DFMA snap-together joints' strength. In light of my culpability and being beyond the time frame Home Depot might exchange the machine, I used an old hose clamp around the collet base to prevent the leaf springs from popping out. I finished another three hours of trimming without the popping problem. I guess I am happy again.
This entry was submitted by Kirk Miller and edited by Rob Spiegel.
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