The following points highlight the top four operations of planing in the industries. The operations are: 1. Planing Vertical or Angular Surfaces 2. Gang Tooling 3. Double Cutting Tool Boxes 4. Hot Planning.
Operation # 1. Planing Vertical or Angular Surfaces:
In such cases, the side-head may be used to advantage. If the cross- rail tool head is to be used then the tool block must be set at an angle as shown in Fig. 15.9 (a), by loosening bolts B, which permit it to be swivelled to the right or left from its vertical position.
The purpose of swivelling is to prevent the tool from dragging over the planed surface in the return stroke. The angular position of the tool block does not affect the direction of movement of the tool, as this is governed by the position of the slide which is set vertical. For planing a vertical surface, first the saddle is adjusted horizontally along the cross-rail until the tool is in position for taking a cut.
The tool is then fed down by hand, until the cut is started, after which the vertical feed is engaged, thus causing the slide and the tool to feed downward a certain amount for each stroke, while the saddle remains stationary on the cross-rail. Before taking cut, it should be ensured with a square that the tool slide is perpendicular to the platen surface.
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For planing an angular surface (inclined at angle θ) with the base, the tool head is set at angle θ (as worked out below) w.r.t. vertical by loosening bolts B’ and turning the base until the graduations on base show so. For obtaining true taper surface, angular planing is based on the application of feed movements simultaneously to the saddle and tool slide so that the tool is caused to move along a path which is the resultant of the feed components obtained at a constant ratio.
Obviously tool down travel and cross feed have to be powered. In Fig. 15.10, surface AC is the angular surface to be planed at angle θ to the planer table surface and for this the top slide of planing head must be swivelled by angle δ.
Knowing the values of cross feed and down feed, value of y and hence 8 can be calculated. The tool block is also set at angle with slide, for planing angular surfaces, so that the tool will swing clear on the return stroke. The top of the block should always be turned away from the surface to be planed, to prevent the tool from dragging during the return stroke.
Operation # 2. Gang Tooling:
Planing with two or more tools simultaneously. (Gang tooling). The use of both cross-rail tool-heads simultaneously is very common on some jobs, depending on their shape and the location and widths of the surfaces to be machined. In such case the two tools should be set such that the leading tool starts taking cut first.
Gang or multiple planing operation is also possible in cases where a number of duplicate parts have to be planed. In this way much time can often be saved by arranging the casting in a straight row along the platen of the planer. This method can’t always be employed to advantage as the shape of the work or location of the surfaces to be machined sometimes makes gang planing impracticable and even impossible.
Planing in comparison to milling is cheaper if number of machine beds to be produced, using gang tooling, is less because initial cost of planing tools is low. The setting up and grinding of planer tools is easier and cheaper. Quick change multiple tool holders are also available in which tools are set on steel plates and pre-set remote from the planer machine.
Operation # 3. Double Cutting Tool Boxes:
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In order to save the ideal return stroke on planers, tool boxes capable of cutting on both forward and return strokes, have been developed. Rigidity of both strokes is the most important criterion in design of such tool boxes.
In one type of double cutting tool box, the tool holder carries two opposed carbide tips, and an oscillating arrangement is used such that these carbide tips are swung automatically through some angle at the end of the table traverse. The holder is swivelled through this angle so that one tip rotates down in to the cut while the other tip rotates up and away from the work.
Operation # 4. Hot Planning:
It has been found that the metal removal rate is improved by 5—7 times when planing hot, particularly with materials like manganese steels. A plasma arc is fitted to heat the work directly in front of the cutting tool so that the heating effect is localised. In this way metal to be cut is softened and the body of the workpiece remains comparatively cool and is not subjected to distortion.