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of 0.250-inch to 0.375-inch width should be used for cutting curves; blades of 0.50-inch to 0.75-inch widths should be used for straight ripping or cutting large-radius curves. The diameter of the band saw wheels will determine the maximum thickness of the blade. The thickness of the blade increases as the diameter of the wheels increases.

Special band saw blades, called “skip tooth” or “buttress” blades, have been developed for soft materials such as plastics and are available with 2, 3, 4, or 6 teeth per inch. These blades should be used when cutting thicknesses greater than 0.472 inches. These blades are hardened and will retain their sharpness for long periods when used only for cutting Plexiglas® acrylic sheet.

Variable pitch (number of teeth per inch) blades work well in reducing chipping when cutting sheet 0.472 inches thick or less.

Band Saw Operation

The tension on the saw blade should be just enough to prevent slipping on the wheels, but not enough to stretch the blade and cause misalignment. The guide rolls or blocks should be set so they just miss the teeth but support the rest of the blade width. They should be set so that their rotation can be stopped with pressure from the thumb and forefinger when the saw is turned by hand. The backup roll should be adjusted so that it does not turn when the saw is idling, but will provide support while the saw is cutting. When cutting formed sections, it may be neces- sary to raise the upper guide. When this is done, extra care is necessary to insure proper alignment. For added safety, the

u p p e r g u i d e s h o u l d b e a s l o w a s p o s s i b l e ( w i t h i n 1 2 i n c h o f t h e

Plexiglas® acrylic sheet).

The action of the saw carries sawdust from the Plexiglas® acrylic sheet and the masking paper onto the wheels. The dust builds up on the wheels and may cause the blade to run off. Therefore, this accumulation of dust must be removed. Stiff-bristle brushes can be placed so that they touch the tires and clean them as they revolve. The brushes should be held with a light spring tension so that they will make contact, yet not cause excessive wear on the tires.

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Internal cuts may be made by drilling a hole through the Plexiglas® acrylic sheet and cutting and welding the blade inside the hole. Once the internal cut is completed, the blade must be recut, removed from the hole, and rewelded. This technique may be useful for special jobs but is too time-consuming for production use.

When cutting unmasked Plexiglas® acrylic sheet on a band saw, special care must be taken to prevent scratching. The saw table must be kept clean and should be free of nicks or burrs. Kraft paper or cardboard should be placed on the table under the unmasked sheet. Tape or rubber cement can be used to hold the paper and the Plexiglas® acrylic sheet together to ensure that both will move through the saw together. When trimming flanges on formed parts, the flange will slide on the saw table so any scratching will not be objectionable for most applications.

F o r o t h e r c u r v e d w o r k , a p i e c e o f w o o d a b o u t 1 2 - i n c h t h i c k b y

1.0 inch wide can be run partially through the saw and clamped to the saw table at the ends. The main portion of the acrylic part will be raised slightly above the saw table, while the kerf is supported by the wood strip.

For Plexiglas® MC acrylic sheet, band saw blades should be of the edge-hardened metal-cutting type with raker set or broach-style teeth. Blades should have 10 to 14 teeth per inch. Speeds should be between 2,300 and 5,000 feet per minute. In general, the thicker the stack of material, the slower the blade speed should be to avoid overheating. Blade speed and material feed and thickness should be such that each saw tooth cuts a clean chip. The welded joint of the blade should be smooth and carefully aligned to prevent chipping or cracking of the material during the cutting operation. A band saw cut should not be considered a finished edge and, if not a rough cut, should be further finished by scraping.

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