The Technique of FURNITURE MAKING

PORTABLE SANDERS

The perfect sander hardly exists and the ideal would probably be some form capable of 'random orbit'. At the present time the following types are used: (a) flexible disc sander grinders; (b) dustless belt sanders; (c) orbital and oscillating pad finishing sanders. Type (a) is of little interest to furniture-makers and is, therefore, not considered, while type (b) is the best compromise between disc and pad sander for the rapid removal of stock, but requires greater care in working.

Dustless belt sanders

Available in belt widths of from 21/2 in (63:5 mm) to 4 in (101 mm), with belt speeds from 1000 to 1700 ft per min. (304 m to 518 m) over a pad size or effective sanding area of about 6 in (152 mm) long by the full width of the belt—the 3 in (76 mm) model is the best compromise between weight and power. The vacuum unit incorporated usually sucks about 80 per cent of the fine dust into the detachable bag, and therefore the cutting action is not impeded by the loose dust and is considerably faster in consequence. For the rapid removal of 91 Biscuit jointer in use for drawer construction, both as a groover to take drawer bottom and also to produce the biscuit joint to fix drawer sides to the drawer front (one biscuit in position)

92 One plunge of the cutter produces identical slots for the compressed hardwood biscuits

stock in wood, metal or plastics these machines can be extremely useful but care should be taken with veneered surfaces as they are inclined to dub over at the ends and cut through the veneer unless waste pieces of material are positioned at each end to prevent the belt dipping. Most models are designed to cut against the belt rotation for easier control, and the direction of the cut should be at a slight

93 Portable sanders: direction of cut

angle (93B) rather than with the grain (93A). The tool works under its own weight and no bearing down to increase the rate of cut should be attempted.

A very recent addition to the range is the Elu MHB 157 Electronic. With its variable speeds it has many advantages similar to those of the electronic router in that power is always maintained under variable work loads. With the addition of the sanding frame attachment, and used at the correct speed with paper of the appropriate grit, quite sensitive sanding of veneers, for example, is now possible with safety. Although this makes the belt sander more versatile and ideal when only one portable sander can be purchased, as it can remove heavy stock and produce a fine finish, the pad finishing sanders are still preferable for final finishing of cabinet work.

Pad finishing sanders

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

96 Heavy duty single speed orbital sander

the case, the lightweight electronic model is probably all that is ever needed.