Dake Model Johnson J Saws - Manual (Page 13)

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13
BLADE SELECTION
Saw blades should be selected by choosing the blade that will give the best results at the
lowest cost. Type of material and the speed at which it must be sawed determine the choice.
Listed below are general factors affecting blade selection.
1. Blade Type.
(a) Carbon Steel – Can be used to cut all types of ferrous, non-ferrous and
composition materials except alloys containing high percentage of chrome and
nickel. Limiting factor: low resistance to heat.
(b) Bi-Metal – Designed for cutting ferrous metals in production cut-off
applications. Developed to saw high alloy materials that cannot be cut
economically by other means. Can be operated at higher speeds and greater
feed pressures than carbon steel blades.
2. Tooth Style.
(a) Standard – Zero degree rake angle and full round gullets. Best suited for
cutting ferrous and non-ferrous materials.
(b) Skip Tooth – Basically the same as standard except for more widely spaced
teeth. Provides added chip room when cutting non-ferrous materials.
(c) Hook Tooth – Similar to skip tooth except teeth have positive rake. Effective
in sawing non-ferrous metals and large ferrous sections when heavy feed
pressures are required. Fast cutting.
3. Tooth Spacing.
Tooth spacing is determined by hardness of material and/or the cross-section.
The harder the material, the more teeth per inch. Thin cross-sections require
more teeth to avoid straddle. Rule: at least 3 teeth in contact with work.
4. Tooth Set.
(a) Raker – Most widely used. Consists of a repeated pattern of one tooth set
left, one right and one tooth straight. Recommended for production cutting
where material is of uniform size, shape and type.
(b) Wavy – Has groups of teeth set alternately to the left and to the right forming
a wave-like pattern. Used for cutting thin stock or where the work varies such
as in pipe, angles, channels and extrusions.
BLADE REMOVAL
1. Raise frame a few inches above bed and close feed cylinder valve to hold frame up.
2. Remove necessary guarding and blade cleaning brushes.
3. Turn blade tension screw counterclockwise and pull idle wheel toward center of machine.
4. Push blade down out of blade guides and remove blade from machine.
BLADE INSTALLATION