diploma mechanical engg student: March 2011

Friday, March 25, 2011

QUICK RETURN CRANK MECHANISM

shaper operates by moving a hardened cutting tool backwards and forwards across the workpiece. On the return stroke of the ram the tool is lifted clear of the workpiece, reducing the cutting action to one direction only. The workpiece mounts on a rigid, box shaped table in front of the machine. The height of the table can be adjusted to suit this workpiece, and the table can traverse sideways underneath the reciprocating tool which is mounted on the ram, the table motion is usually under the control of an automatic feed mechanism which acts on the feedscrew. The ram slides back and forth above the work, at the front end of the ram is a vertical tool-slide that may be adjusted to either side of the vertical plane. This tool-slide holds the clapper box and toolpost from where the tool can be positioned to cut the straight, flat surface on the top of the workpiece. The tool-slide permits feeding the tool downwards to put on a cut it or may be set away from the vertical plane, as required.
The ram is adjustable for stroke and, due to the geometry of the linkage, it moves faster on the return (non-cutting) stroke than on the forward, cutting stroke. This action is via a slotted link or whitworth link.
Cutting fluid may be employed to improve the finish and prolong the tool’s life.

The shaping process was used in the early days of machine tools. Shaping machines are not widely used now. Shaping produces flat surfaces by moving a single point cutting tool in a recprocating motion. The forward stroke is the cutting stroke the backward movement is completed at a faster velocity and includes the sideways feed motion.

The shaping machine is a versitile machine able to produce flat surfaces , grooves, T-Slots, dovetails, and may be used to produce curved surfaces.

The size of components that may be machined is normally limited by the length of the stroke of the shaping machine which can vary up to a maximum of about 1500mm. (750mm is normally the maximum stroke. The shaping machine is not generally used as a production tool because of its slow cutting speed and the unproductive return stroke.