Thanks to Graham R. for this one, and his experience with the retaining screw on his Bosch jigsaw.He writes:
The cutting angle on my Bosch jigsaw can be changed by loosening a screw, moving the shoe round, and retightening. This will be done more than once-in-a-lifetime, maybe more than once in a day, and of course the shoe has to be solidly fixed. The retaining screw has a fairly chunky head, and from the outside looks as if it will take the necessary amount of welly. After you've stripped the thread on the third or fourth time of use, however, you look inside and find that it has (had!) a 0.5mm thread more suited to a clock than a power tool (see pic left).
I replaced the screw with something heftier, putting a plastic collar round the new nut to bring it up to the right size and hold it still until the tightening action secures it properly (see pic below), and I've not had any more trouble.
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Comments (2)
I guess the designer used a fine thread to (a) provide a large enough clamping force without so much torque and (b) to reduce loosening under vibration.
However the average user will expect to apply the "obvious" amount of torque, which in this case is too much - a plastic wing-nut would limit, and indicate, the torque.
A good case for Donald Norman, "The Psychology of Everyday Things"
Posted by Rod Dalitz | April 6, 2011 11:29 AM
Thanks Rod. That sounds a good point to me. And I'm glad you mention that book - I'd recommend it, too. It helps open your eyes, and is one of the things that inspired the Impossible Objects series (it had the 'impossible coffee pot' on the cover, didn't it?).
Posted by Alun Williams - Electronics Weekly.com
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April 8, 2011 5:18 PM