Maschinen Gonstrueteur, No. 18, gives a short description of a new tool for dressing stone, which is now on exhibition at Paris, built by Brunton and Trier, Batersea Foundry, London, England. A large, hollow face-plate is bolted to a hollow spindle, which is rotated by means of a pulley fastened to the same. The face-plate carries, near its outer edge, a number of small disks, placed at an angle to the central axis, and which have a double motion--firstly, around the axis of the main spindle, and then around their own. The mechanism is arranged to let a point of the disk's sharp edge describe a curve of a cycloidal nature on the face of the stone. There is, consequently, but little friction, which is very evident to the observer, as no sparks are visible~ even while operating on the hardest material. The disks retain their sharp edges for a considerable length of time, and do not even heat.
Through the hollow spindle runs a solid one, carrying a bevel gearwheel, which is inside the face-plate, and does not rotate, as a rule, but gives motion, through separate bevel-pinions, to the disk-spindles, whose bearings are in the face-plate. When, however, the diameter of the disks has been reduced by grinding, so as to impair the cycloidal nature of the curve before mentioned, it is necessary to give the central wheel a slow motion, to correct the error. The whole can be fed to and fro in the direction of the axis, to regulate the depth of the cut.
The machine is provided with several tables, which, besides the ordinary sliding surfaces and rack for propulsion, also have wheels, allowing the tables to be changed, and the work to go on uninterruptedly.
The machine on exhibition can dress a surface 1"4 metres (4 ft. 7-1 in.) wide, the length depending only on the length of the table or bed. The face-plate makes 100 revolutions per minute, each of the 12 disks, 600. The diameter over the outside of the disks is 1"8 metres (5 ft. 10"9 in.).
Owing to the high rate of speed, the disks, 30 cm. (11" 7 in.) in diameter, can be made of very hard, chilled cast iron.
An idea of the capacity of this machine, may be gained from the following data :