BURR

BURR

Burrough's BURROUGHS's MACHINE for grinding and polishing glass, invented by Mr Burroughs of Southwark; and for which he received from the society for the encouragement of arts a premium of 70l.

Plate CXXXI.

This machine consists of a cog-wheel A (fig. 3.), 12 feet in diameter, carrying 72 cogs; which turn a trundle-head B, one foot four inches in diameter, and furnished with eight rounds; and also a horizontal spur-wheel C, of 12 cogs; and one foot eight inches in diameter. The trundle-head B turns a spur-wheel D of 10 cogs, and two feet eight inches in diameter. This spur-wheel has two cranks, a b, in its shaft; one of which a gives motion to a wooden frame, c, about 34 inches long and 19 broad. On the under side of this frame are fastened by screws 12 pieces of polished metal, each five inches and a half long, and three broad, covered with leather; and underneath these polishers a glass-plate cemented in another frame is placed on the bench d, and polished with tripoli by the motion given to the upper frame by the crank a. The nuts of the screws which fasten the polishers to the upper frame are not screwed close to the wood, in order to give the frame room to play; by which contrivance the perpendicular rise of the crank is avoided, and the motion of the polishers is always parallel and equal. The under frame may be moved by the hand in any direction without stopping the machine; by which means the plate, when larger than the polishing frame can cover in its motion, will be equally polished in every part.

The other crank b gives motion to two other polishers marked n, o, which have an alternate motion by the bending of the crank; they move upon the same plate, and have an equal number of polishers as that already described.

The same crank also gives motion to a contrivance represented at e for polishing spectacle-glasses. It consists of two segments of the same sphere; one concave and the other convex. On the latter the glasses are cemented; and polished by the former, which is moved by the crank b. The convex segment may be moved round by the hand without stopping the machine, so that all the glasses on its superficies will be equally polished.

The other spur-wheel C, by means of a crank in its shaft, gives motion to another frame g, employed in grinding the glass plates. The rod h, extended from the crank f to the frame g, is fastened to the latter by means of a pivot, in order to admit of a rotatory motion, as well as that given it by the crank in a longitudinal direction. This rotatory motion is effected by means of a rod of iron i, called a trigger, sharp at the extremity next the frame, where it touches the teeth of a horizontal spur-wheel, or circular piece of wood, fixed on the grinding plate, while the other end is extended three feet two inches to the centre of motion.

But this contrivance, in which the merit of the machine principally consists, will be much better conceived from a small delineation of it by itself (fig. 4.), where F is the crank marked f in fig. 3., and turned by the spur-wheel C in the same figure. G is the trigger, three feet two inches long. I, a roll fixed on the trigger for the rod to slide on. H, the horizontal spur-wheel, eleven inches in diameter, fixed on the grinding plate; the teeth of which are touched by the trigger; but with a very unequal force, as it will wholly depend upon the Burrough's grinding-plate's being farther from, or nearer to, the Machine centre of motion of the trigger. By this simple contrivance, the grinding-plate has a very compound motion, never moving exactly in the same track, and therefore must grind the plates equally in every part. Several attempts have been made by others for producing the same effect; but without success; the grinding-plate always follows the same track, and consequently the plates are ground equally.