By means of springy tools and soapy water, also a smooth filing, a plug, whether a small one or a large one, may be nicely smoothed to fit the proper hole which allows the necessary quantity for grinding the plug to its final diameter. Only by care in the turning can the grinding be effected with some degree of comfort, and without a great consumption of time. To facilitate the making of a large number of plugs, it is usual to perform the grinding with a lathe specially adapted to the purpose. Such a lathe requires no gear for slow movements, nor any delicately finished machinery that would be injured by the emery falling about. The tools that belong to such a lathe consist of cans or boxes having lids to contain emery of two or three sizes - a reservoir of oil and emery, which is suspended so that the mixture may run easily to the work - and a few grinders. A grinder for plugs and other cylindrical work consists of a pair of grips made of lead or wood; these are of various sizes to suit work of various diameters, and each pair of grips are jointed together at the end for grinding, and are held together at the other end with a bolt through a hole in each arm or handle of the tool, Wood grinders of this shape may have two or three grinding gaps, similar to those shown in Fig. 529, and a gap which is too large for the particular work in hand is made to suit the work by placing pieces of sheet lead between the wood and the surface to be ground. The grinding surfaces of all the gaps should be hollowed, to form recesses in which the emery and oil will collect, instead of being quickly rubbed off with the edges of the grips. The process of grinding by such means consists in rotating the plug in the lathe while a pair of grips is fixed tight to the surface to be ground, and while in contact a traversing motion which is parallel to the length of the lathe is imparted to the grinder, by which a smooth circular form is given to the work being ground, and without this movement, together with the rotary motion, a cylindrical form cannot be produced; if the traverse of the grinder ceases only a few seconds, the work is disfigured with circular grooves around the surface, and is in danger of being spoiled. In order, therefore, to continually move the grinder, it is moved to and fro with the hands of the operator, or by means of the lathe-traverse. This traverse is termed coarse, because the wheels are of proper sizes to produce a much quicker movement along the lathe than would be required for turning. The length of the hole in a grinder is about equal to the thickness of the work to be ground, if it is about three or four inches in thickness; but for work about one or two inches thick the length of the hole is about twice the diameter of the work. During the grinding, emery and oil is applied either by a pipe from the reservoir, or applied with a brush by the operator, and the traversing motion is continued to and fro along the entire length of the work, if it is parallel and needs an equal reducing; but if one portion is too thick, while other parts are of the required thickness, the grinder is moved only along the thick portion until sufficiently reduced.

The grinder-frame shown by Fig. 530 is bolted to the saddle or carriage of the lathe, and is provided with a jointed cap in one end of which is a screw-bolt for applying the pressure necessary for grinding. The grinding grips which belong to the frame are of lead, and of various sizes and thicknesses to suit various work, and the emery and oil or diamond-dust are applied to the work through a hole in the middle of the cap. This hole is large enough to hold the end of a pipe belonging to a feed-cup which is put on to the cap when grinding is to be effected. A frame of this class is suitable when a large quantity of* reducing is to be effected, which occurs when a plug has been distorted with hardening and requires three or four days' grinding. In order to accommodate the frame to the work when it does not rotate truly, the frame is loosely bolted to the saddle to permit a small movement which effects the accommodation required. A grinder frame which is provided with a joint in the middle may be tightly bolted to the saddle, instead of loosely, which is necessary for a frame without an accommodating joint.