Re: Re: Engraving and engine turning

Thanks Pete,

As mine is such a small machine, I was considering a simpler method of
backlash adjustment. The feedscrews are only basically normal threads
(not ballscrews) and are 1mm pitch. The nuts are made of bronze and are
cut across for 3/4 their width part way down the thread and a screw is
installed to nip the two parts together - the same effect as having two
nuts sprung apart on the thread. This way I can have a relatively long
nut to equalise any minor irregularities in the screw pitch whilst
keeping the main part of the nut always pressed up against one side of
the thread by just the right amount. This is a more effective method
than having two half nuts clasped around a thread.

Regarding the Tensator spring thing, I'm not sure it is the same
Tensator I know. The one I know from clocks - and which I thought was
the only one, needs two cylinders to wrap around. It is made in the same
fashion as a pocket tape measure spring, dished along its length and has
a natural tendency to straighten itself out. In clocks, it is this
force, rather than the more normal tensioning of a spiral spring which
is used to provide the drive. The spring you seem to describe is more
like a normal coiled spring and would follow Hookes Law 'Ut tensio, sic
vis' giving a non-linear force.

Ian

Pete Jarman wrote:

> The way Turner used a "Tensator" spring was to fix the outer end of the
> spring to the quill and the spindle fixed to the centre of the coil to the
> underside of the quill housing with a suitable bracket which allowed the
> spindle to be rotated and locked to set the preload. As the quill is lowered
> the spring is wound up. If you used this with a feedscrew it would give you
> the necessary preload of the nut against the thread to eliminate the
> backlash. I'm considering using this idea to eliminate the backlash in a
> Stent cutter grinder I'm finishing off at the moment.

Best wishes

Ian

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Ian W. Wright LBHI
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Bandmaster and Euphonium player of the Hathersage Brass Band. UK.
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