Two types are available: reciprocating (straight-line), in which the pad moves with a backward and forward stroke to give true straight-line sanding with the grain; orbital, in which the pad is rotated in a series of small orbits of about 1/8 in (3 mm) to 3/16 in (5 mm) diameter. In theory at least the reciprocating type should prove more effective, but in practice there is probably little to choose between it and the orbital type, for with the speed of the cut (4000 to 5000 orbits per min.) there is virtually no scratching across the grain, and in fact a diagonal movement across the grain helps to level out inequalities in the surface. Practically the only drawback with these pad sanders are slight swirl-marks caused by loose grains from the abrasive paper, but if the surface is kept well dusted in advance of the cut they should cause no trouble. The point to remember is that applied pressure does not increase the rate of cut to any appreciable extent, and in fact heavy bearing down may result in the machine itself orbiting rather than the grit.
Various types are obtainable, differing mainly in weight and ruggedness, for the pad size is usually standardized to take a half sheet of 11 in (280 mm) by 9 in (228 mm) abrasive paper. The general pattern is a felt-faced or foam-rubber pad permanently attached to the body with an easy lock and release for the abrasive paper, but models are available in which the pad is removable for wet and dry sanding and for contour sanding with thick foam pads. Dust-extractors are fitted to some models, and at least one type has an optional adjustment for either straight-line or orbital sanding built into the machine which offers some advantage, for moulded sections cannot be sanded with the orbital action, but cork counter-profiles can be fixed to reciprocating pads.
Here again Elu have a lightweight electronic orbital model, MVS 156, with stroke speeds from 6000 to 24,000 a minute, but many may find the heavy duty single speed models more suitable. The choice depends on whether portable sanders are the only form of power sanding in a shop or merely an occasionally used addition to the much more efficient floor mounted overhead pad sander. If the latter is
95 Half-sheet finishing sander
96 Heavy duty single speed orbital sander the case, the lightweight electronic model is probably all that is ever needed.
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