Both planers and shapers employ single point cutting tools for metal removal. But in case of shaper, reciprocating motion is given to the cutting tool whereas in case of planer the work reciprocates and tool is given the feed. On shapers, comparatively small work-pieces are machined whereas large work-pieces are handled on the planer because of its capacity of long table travel and robust construction.
Planers are used to machine plane surfaces that may be horizontal, vertical, or at an angle. Angular surfaces are often easier to machine on a planer. Profiled surfaces can be planed to a layout line or to a template if the planer is equipped with tracing attachment. Planning is also the most effective method of machining parts having complex shapes and requiring machining of long and narrow surfaces.
Though some of the work formerly done on planer is now done on planer type milling machines using large-face milling cutters, but it is found that surfaces produced by face milling cutters tend to be glazed or work hardened because of the pressure of the face milling cutter on the work.
This glazed or work hardened surface is difficult to hand scrape. Planed surfaces, on the other hand, are easily scraped since work hardening is kept to a minimum on the surfaces produced by a single-point cutting tool.
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Therefore, plane surfaces required to be hand scraped can best be machined on planers. It is also possible to take multi-cuts at various places in a single stroke as planer can accommodate more than one tool-holding stations. It is also possible to machine large number of smaller parts by setting them properly on the planer table.
Generally it is usual to mount two tool heads on the overhead cross-rail and one each on either side of the columns. In case of planers, the setting time is of the order of 5 to 6 times that for shaper; also the operation of a planer requires a high degree of mental effort and mechanical skill. Best and safest methods of setting up a complex part on the planer table have to be adopted. In general, planers produce heavy work at lowest cost in comparison to any other machine tool.
As the single-point tool is used in the planer, it imposes relatively little pressure on the work and only a small amount of heat is generated. Thus accurate and distortion-free large surfaces can be produced on the planers.
At the same time, it can also be used for a roughing cut of the order of 18 mm depth, and feed of 1.5 to 3.0 mm per cut on the casting surface. After that the fine cuts of depth 0.25 mm or 0.50 mm could be taken for finish and accuracy.
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Like all reciprocating machine tools, the planer is equipped with a clapper box to raise the tools on return stroke. As the tool and holder are quite heavy, air cylinder is employed to lift the tool on the return stroke.
Planer capacity is expressed by the maximum width, height and length of stock that can be planned on the machine. The stroke length of planer varies from 1 to 12 m. Flatness of the order of 0.01 mm can be achieved on workpiece length upto 1.2 m or 0.4 sq. m area. Surface finish of the order of 1 µm can be attained.