Geometric chuck and parts, handmade by John Holt Ibbetson, 1835

This example illustrates the improvements made between the date of the invention of the geometric chuck in 1815 and the period 1835.

Engraved on the faceplate is the following : '/bbetson's Geometric Chuck (1st, 2nd., 3rd, and 4th. parts) invented by Jno. Holt /bbetson, Esq., of His Majesty's Victg. Office. The first of these Chucks was made by him in 1815 and this Chuck, made by his own hands, even to every screw, contains all his improvements on it up to Decr. 1835'.

The rear detent gear wheel has three rows of teeth from which alternative trains of gears can be driven. These are mounted on the rear face of the plate, and drive, by way of a small spindle and gears, the gear trains on a quadrant plate which is carried on the forward face of the faceplate. The quadrant is capable of adjustment by hand or by a worm and worm-sector graduated in degrees. On the spindle on the quadrant plate are various toothed rings interspaced with which are three further quadrant plates carrying selective trains of change gears, and a further worm and sector adjustment. The complicated motions thus generated as the chuck rotates are conveyed to a secondary faceplate, which, in turn, carries a spindle furnished with an eccentric chuck of standard pattern. The work spindle of this eccentric chuck is furnished with a spacing detent and alternative worm and wheel movement with calibrations in degrees on the rim, by means of which the work is set.