A milling machine vise that is very satisfactory for many classes of work is opened and closed by compressed air, which is carried to the various machines in pipes. When compressed air is so used, it is often further employed to clean the jaws. This operation requires a piece of flexible hose having a suitable valve which can be opened so that the chips and dirt can be blown from the jaws. By this method it is easy to get rid of small chips in places hard to reach with a brush. In fact, compressed air is many times used in cleaning vise jaws where the vise is opened and closed by means of a screw or cam, the air being automatically turned on as the jaws open.
When a cam will fasten the work to the fixture strongly enough, it proves a rapid method, and one that is often employed. At F, Fig. 251, is shown a fixture for holding bolts the heads of which are to be straddle-milled. One cam binds two bolts, and as three cams are provided, six bolts may be milled at a time. The fixture is so designed that the cam handles are at the front of the fixture rather than back of the cutters, as in this position the operator's hands would be in danger. The cutter pressure is against the solid part of the fixture, thus insuring rigidity.
At times cams do not prove satisfactory, and it is found necessary to use a screw. Screws are slow of operation, as it takes a long time to turn them back and forth sufficiently to bind or free the work. To facilitate matters, a slotted washer G, Fig. 251, is sometimes provided, and a screw which passes through a hole in the work is used. By this means it is only necessary to give the screw a part of a turn in order to bind or remove the washer thus giving a very quick action.
Fig. 253. Set-Up for Milling Blot across End of Lathe Spindle.
When it is necessary to place the binding device on the under side of a fixture or in some inaccessible place, a wedge-shaped key, as shown at II, Fig. 251, proves satisfactory. It holds the work solidly on to the seating surface, and is quickly and easily operated.
In Fig. 252, at A, is shown a piece of work whose ends are milled square. As the sides are machined on a slight taper to the axis of the piece, it was necessary to hold the work as shown at B, and use an end milling cutter.
Fig. 254. Set-Up on Vertical Milling Machine for Milling Automobile Starter Coven Courtesy of Becker Milling Machine Company. Hyde Park. Massachusetts.
In making fixtures of the kind under consideration, the designer should bear in mind that the simplest form which will insure desired results at the minimum cost is the best. Complicated fixtures should always be avoided, if a simple one will answer.
Fig. 253 shows a method of holding a spindle and milling a slot across the end. The work is held in a fixture made in two parts, and the cut is taken by feeding the knee vertically by means of the automatic vertical feed. With a fixture of this description, the ends of long pieces can be milled as shown.
Fig. 254 shows a fixture for holding work in a vertical milling machine, by the use of which the process of milling is continuous. After a piece is milled, it is removed and another put in its place while other pieces are being milled. For many jobs of flat milling this method is to be recommended as there is no lost time.
The problem in the up-to-date shop is to turn out all the work possible in a day with the minimum expenditure for labor. By this method of milling, the machine is cutting constantly, and the entire time of the operator is employed in taking out, putting in, and gaging the work. This is not the case where a man has several milling machines of the ordinary type to tend; for then the time of the operator is wasted when he walks from one machine to another, and the time of the machine is wasted when it lies idle and unproductive while the fixtures are being loaded and unloaded.