Rooting around in the fascinating stuff at the bottom of a draw labelled 'Engineering - Junk Miscellaneous'. Delving amongst the delightful...
An Engineer in Wonderland – Wooden springs and infinite fretsaws
I was talking to a retired wood worker about a bench-top scroll saw I just bought.
It is the mechanical cousin of the hand-held fret saw, and within it a saw blade under tension moves rapidly up and down cutting what ever you push against it.
The good thing is, by threading the blade through a drilled starter hole, apertures can be cut in sheet material.
Well that is the theory, but I am not getting on too well with it, which is why I approached the expert.
He gave me some tips, and then told me of the one that he used as a professional.
Rather than have an arm running from the base to the top of the blade, like mine has (see photo), the upper end of the blade in the big industrial version was suspended from the ceiling of the huge workshop by a long vertical wooden beam.
With no support arm in the way, any size sheets of wood could be sawn up.
And on one occasion, to get someone out of a hole, an aluminium car roof was slid underneath to cut window apertures.
Guy-wires from the beam to the roof held the support beam steady, and these had to adjusted a few millimetres twice a year, once as the girder-and-asbestos building warmed up in the spring, and again as it cooled in the winter.
At the bottom of the beam was a guided holder for the blade with tension provided by a leather strap connected to either end of a wooden – probably ash – bow spring.
Despite constant flexing at sawing speed by the electric motor in the base of the machine, the wooden spring never needed replacing.
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