Page:Practical Treatise on Milling and Milling Machines.djvu/117

Rh times damages the cutters and machine. It is very essential, therefore, that work be clamped solidly, but in such a manner that it is not sprung.

An assortment of clamps or straps, together with jacks, a shim, step block and clamping bolt, are shown on the opposite page. These accessories form an important part of the equipment of a milling machine, and are needed where a variety of work is done. Several sets of each style of strap, and different sizes of step blocks and clamping bolts should always be at hand for use on work of varied shapes.

Whenever clamping a piece to the table, the straps should be placed squarely across, so as to have a full bearing at each end and, if possible, at points where the work extends down to the table beneath the strap. If it is necessary to place a strap over an overhanging part, such as on the piece of work shown on the next page, some support should be put between the overhanging part and the table, otherwise this part is liable to be sprung or broken off.

Another point in connection with clamping such work is the position of the clamping bolt. It should always be placed as near the work as the slot in the strap or other conditions will permit, for in this position it will exert the greatest pressure on the work and will not require setting up so tightly.

When milling work held in a jig or fixture, it is advisable to have the thrust of the cutter taken against the solid support, not against the removable member, for in this case there is more tendency toward vibrations that might loosen the clamping nuts. When duplicate pieces are milled, using a fixture, care should be taken to clean the bearing points each time before putting

Fig. 59