Re: Re: Engraving and engine turning

>From: "Ian W. Wright" <Ian@...>

>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.
>

There are two types of constant force springs, the type Ian described which
I once used in a clock, where the spring comes off the storage reel and
winds "backwards" onto the takeup reel, to which it imputs a constant
rotational force. The second type unwinds from a reel and imputs linear
force to the thing that unwinds it. I've not seen these, and can't comment
on how constant the force is.

David M. Munro