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W. & S. Butcher


     
 

Masters' Library


 
  Ibbetson's Geometric Chuck, Manufactured by Holtzapffel & Co.    

A Brief Account, & c.

The object of this Memoir is to bring under the notice of the Public particularly under that of the Amateur Turner and of those who take pleasure in the investigation of the organical description of curves the powers and capabilities of the Instrument alluded to in the title page.  

In Turning and Mechanics I am self-taught and an Amateur only, but as I contrived the Instrument and constructed it with my own hands, even to every screw, from the raw materials of brass and steel, it is fair to conclude that I must be better acquainted with its working powers than those who never saw it, and who, consequently, can know nothing whatever about it.  This is so selfevident that I should not have made the remark had not some writers in the Mechanics' Magazine pretended to lay down laws regarding it, which are quite at variance with my views and with what I know to he the fact.  The power of describing Spirals has been ascribed to it, which I had previously explained, in that publication, it could not do.

I am at no loss to produce spirals by means of my Turning Apparatus, as the following Specimens, which I executed by it, will prove ; but, I say that the Chuck I have contrived is not capable of producing them; and, further, that not any instrument, which is attached to the mandril of the lathe and works round with the mandril, can be so constructed as to move a plane against a fixed point in such a way as to describe the curves these Specimens exhibit. Every curve that can be generated by compound circular motion has a tendency to return into itself, and must eventually do so if sufficiently extended. The spiral is a curve which is constantly receding from itself, and its very properties are, that, it may be infinitely extended; and it, therefore, never can return into itself.

The motion of the mandril is a fixed circular one, and is the primum mobile of the Chuck; and, therefore, let the motion of the Chuck be what it may, the combined motion of the mandril and the Chuck can never so move a plane against a fixed point as to describe a spiral.  A figure, bearing the semblance of an ellipsis, may be patched up from portions of circles or spirals, but such a figure will not be the more an ellipsis because the maker of it choses to call it so.  The writer to the Mechanics' Magazine has completely fallen into this error: he chooses to call a curve he has produced, a spiral; and because he calls it so, has vanity enough to suppose that others will agree with him that it is so.  The mandril, he states, must only be turned half round (rather a novel way, it will be said, of working the lathe), because when the mandril has been turned half round, the spiral returns into itself, being (he says) a new property in the curve he has discovered.  Sublime and astounding discovery indeed!!! The mind had better be a perfect blank than imbued with error and nonsense.


JOHN HOLT IBBETSON
November, 1833


 
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