Radial Arm Saws

The radial arm saw is designed for accurate crosscutting, mitre and bevel sawing. Both the saw head and motor are suspended on a rigid horizontal arm above the table. Raising or lowering the arm adjusts the depth of cut. A familiar machine in the joinery workshop, the radial arm saw cuts joints such as tenons, rebates and housings precisely. Unlike the table saw, timber is stationary while being sawn, held against a rear fence. The machine is normally positioned against a wall, so it is usual to build long, narrow tables either side to support the timber being sawn. They may even include rollers to help slide heavy boards into position.

Machine Basics

The machine is normally mounted on a sturdy stand, but can also be bolted to a purpose-built unit. You should fit a sacrificial board (such as MDF) to the table: the saw blade cuts into the surface about 2 mm (1/16 in) when it makes a crosscut or mitre cut, and the more angles and bevel cuts you make, the more this board starts to disintegrate and needs replacing.

To make a cut you simply grip the handle and pull the blade across the table. A spring ensures the saw head returns when the cut is completed. A lower guard encloses the blade until you begin to pull the saw head outwards, when it opens up to expose enough of the rotating blade to suit the depth of timber being cut. It then retracts automatically at the end of the cut. An adjustable guard is located in front of the blade below the handle. To adjust blade height, you rotate a cranked handle or knob at the rear, which raises the arm via a rack-and-pinion action. The blade parks automatically behind the fence at the end of a crosscut pass.

Induction motors fitted to radial arm saws are fairly quiet and rated between approximately 1,500 and 2,000 w. The blade rotates at about 3,000 rpm. The on/off switch is located conveniently at the front of the arm.

Blade diameter is between about 254 and 350 mm (10 and 13 ¾ in). Cutting depth is around 68 mm (2 11/16 in) at 90 degrees on smaller saws, up to 110 mm (4% in) on industrial machines.

EXTRAS

On most radial arm saws it is possible to mount a small router for overhead machining, although you are likely to be restricted by model compatibility. The tool fits into a cradle below the arm. Drum and disc sander attachments are also useful options on this machine. Dado heads can be fitted for trenching, grooving and rebating across the grain, although you should always clamp timber securely to the fence for this operation.

Crosscutting and Ripping Timber

Crosscutting capacity is determined by the length of the arm. It varies from about 380 mm (15 in) on a small saw up to 610 mm (24 in) on bigger machines. For repeat cutting, clamp an offcut to the fence to act as a length stop. You can rotate the saw head through 90 degrees for ripping timber or panels to width, although this is less satisfactory than using a table saw. In this mode the saw blade is parallel to the rear fence, which guides the timber as you saw. You adjust the width by sliding the head along the arm and locking in position. Most radial arm saws will cut panels at least 610 mm (24 in) wide, or half a standard-size sheet.

A riving knife is lowered behind the blade when ripping. When you revert to crosscut mode, the knife is raised and stored inside the blade guard. To prevent timber being thrown back if the blade jams, anti-kickback pawls are provided. Fitted on an adjustable arm in front of the blade, lower them to make contact with the work piece, and raise them clear of the timber when crosscutting. Always use a pushstick when ripping material.

Mitre and Bevel Cuts

Indexing at 90 degrees and 45 degrees makes it straightforward to saw at these common angles by swinging the arm around and locking with a clamping lever. A protractor scale at the rear of the machine enables you to lock the arm at any angle to the right or left of the centre (90 degree) position. For bevel cuts, ou tilt the saw head over and lock in place. Again, indexing at 90 degrees and 45 degrees is normal.

Word Discription :

Crosscutting Sawing across the direction of the grain.

Kickback When a work piece is ejected from a machine towards the operator by a rotating cutter or blade.

Pushstick A wooden or plastic safety device used to push narrow or small components past the blade on a saw. Prevents fingers getting too close to the moving blade.

Ripsawing (ripping) Cutting parallel to the grain of the timber.

Riving knife A curved steel plate fixed behind the saw blade to prevent timber closing up and pinching as it passes through the blade. Slightly less than kerf width but wider than blade thickness.

rpm revolutions per minute

TCT Tungsten carbide tipped

w watts

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