Abrasive Saw Blades

CHOOSING THE RIGHT CUT-OFF WHEEL

Selection of a wheel for any cutting job involves several factors. The desired end result is usually most important, whether it involves high-speed production cutting, or a precision, fine finish cutting application. Knowing the following information can help in the selection process.

MATERIAL - Type of material to be cut: it’s hardness, size and shape, quality of cut sought.

MACHINE - Type to be used: chop-stroke, oscillating or swing-frame, make and model, size, horsepower, spindle speed, how the workpiece is secured, wet or dry cutting.

WHEEL - Dimensional features of wheel currently in use: diameter, thickness, arbor and reinforcement pattern, manufacturer’s specifications (name, grade, rpm).

Use a soft grade when:
• Machine has low horsepower.
• Good finish is important
- fine grains normally used to provide minimum burr.
• Operators cut slowly.

Use a medium grade when:
• Softer grades do not provide enough cuts
- longer wheel life is required.
• Cutting normal materials. Machine horsepower will support faster cutting rates.

Use a hard grade when:
• Maximum wheel life is sought.
• Machine has adequate horsepower (1 hp per inch of wheel diameter is recommended).
• Burr and finish requirements are minimal. (note that fast cuts will produce a reasonably good finish)




A GENERAL GUIDE TO
MAGNUM WHEEL GRADE CODE





ABRASIVE WHEEL
REINFORCEMENT CONFIGURATIONS















ABRASIVE WHEEL COMPONENTS

The abrasive wheel brings thousands of miniature cutting tools (abrasive grains) into contact with the work-piece, in rapid succession, as the wheel spins. These grains are harder than the metal alloys being cut, and each individual grain removes a small chip of metal as it comes in contact with the workpiece repeatedly, at high speed. This results in the rapid cutting of the material.

The design and manufacture of high quality cut-off wheels requires a knowledgeable integration of key components:

ABRASIVES - Several kinds of abrasives are commonly used; Aluminum Oxide, Silicon Carbide, and Zirconia - Aluminum Oxide; all designed with variations in size and structure, to significantly affect the specific cutting or grinding application.

BOND - The bonding system holds the abrasives together in the wheel shape. Consisting of resins & fillers, it allows the wheel to wear away at a specific rate, to achieve the required cutting action. Wheels with tenacious bonds are called “hard”; those that break down more rapidly are considered “soft”. Resinoid bonding systems are used for dry-cutting of most materials. Rubber-Resin bonding systems are used for most wet-cutting applications.

STRUCTURE - To provide space for the abrasive grain - bond matrix, the wheel must be constructed with the proper number, size and distribution of minute “spaces” in the structure. Structures with more spaces are considered “open”, those with fewer spaces are considered “closed”.

REINFORCEMENT - For added strength, a woven fabric of long strand fiberglass, impregnated with phenolic resins, is molded into the wheel during the manufacturing process. The strand size, weave and strength is determined by the requirements of the cutting job, and is engineered to meet the stresses of the application.



TROUBLESHOOTING CUTTING PROBLEMS

PROBLEM: Excessive wheel wear
    CAUSE: Cutting too fast.
    CAUSE: Wheel grade too soft.

PROBLEM: Burned cut surface
    CAUSE: Cutting too slow.
    CAUSE: Wheel grade too hard.

PROBLEM: Broken wheels
    CAUSE: Wrong wheel for the job.
    CAUSE: Wheel grade too hard.

PROBLEM: Wobbling
    CAUSE: Worn flanges or bearings.
    CAUSE: Warped wheels.

PROBLEM: Crooked cuts
    CAUSE: Worn flanges or bearings.
    CAUSE: Poor clamping.
    CAUSE: Warped wheels.

PROBLEM: Glazing of wheel
    CAUSE: Cutting too slow.
    CAUSE: Belt slippage.
    CAUSE: Wheel grade too hard.



EVALUATING WHEEL FUNCTION

Notice how much pressure is required to feed the wheel through the work. The material should cut easily.

Listen to the “sound” of the wheel as it cuts. A wheel that is cutting properly requires less power and pressure to work, will be substantially free of burn or burr, and cuts straight, with less noise.

Pay attention to how the wheel edge is wearing down.



INSPECT WHEELS
FOR INDICATIONS OF TROUBLE

To prevent serious damage to wheels and equipment, stay aware of your machine's cutting action by inspecting the edge of the wheel for signs of trouble.



ROUND FACE (fig 1) - Normal when using the correct wheel to cut large solids.

SQUARE FACE (fig 2) - Normal when using the correct wheel to cut small solids, structural shapes, medium wall pipe and tubing.

CONCAVE FACE (fig 3) - Normal when using the correct wheel to cut tubing and thin-wall sections.

POINTED FACE (fig 4) - Indicates wheel is too hard. May cause binding, breakage and excessive burr on the cut.

CHISEL FACE (fig 5) - Wet cutting problem. Usually indicates wrong application of coolant. May cause breakage and crooked cuts.

GLAZED SIDES & FACE (fig 6) - Indicates wheel is too hard or cutting too slow. Requires excessive pressure and power to cut. Causes breakage, excessive burr and burn.