Epicycloidal cutting frame/Ellipse Cutting Frame with outrigger for slow drive, with 3/8" square shank, maker unknown

This instrument, introduced by H. W. Pomeroy about 1870, is a development of the elliptical cutting frame.

The cutting frame is held in the slide-rest by a hollow square stem. Rotating on the rounded front end of the stem is a two-speed pulley directly fixed to the plate it drives. The latter carries a radial arm pivoted at one end near the edge of the plate and clamped at the other end by a thumb screw which slides in a curved slot. The frame carrying the cutting tool rotates in a bearing formed in the radial arm and is driven through a train of wheels terminating in a wheel central with the driving plate and fixed to a spindle which passes through the hollow stem. At the rear the spindle is held by a worm engaging in a wheel to which it is attached. Eccentricities are set on the cutter frame and radial arm by screws, and the axis of the arm being also the axis of one wheel of the driving train, radial movement of the arm does not throw the wheels out of gear. For cutting ellipses the gear wheels are arranged to give a relative speed of rotation in the two parts of the cutter in the ratio of 2: 1 in opposite directions. By varying the eccentricities all manner of ellipses can be drawn from a straight line to a circle, and by means of the worm and wheel at the back they can be placed in any angular position. For the production of cycloidal curves the ratio of 2: I is altered by the introduction of other wheels into the train.