Sharpening of the Teeth

Generally

In order to sharpen saw blades for the machine frame saws it is necessary to use a machine grinder manufactured for this purpose. The grinder must be properly adjusted and the guiding bar (grinder movement) must be precisely manufactured not worn in order to avoid over sharpening of the teeth into various pitch. If this is occurring then it is necessary to have the grinder adjusted by a professional and have the guiding bar reground by a professional service.

The grinding shop personnel must be qualified accordingly for this activity and made aware about the possible risk resulting from working with sharp tools.

The grinding shop should be well lit.

Main Principals During Sharpening

  1. all of the teeth must have the same (proper) profile after sharpening
    • height
    • pitch
    • rounding of tooth gap (foot radius)
    • cutting angles
    • for inspection, it is suitable to use a tooth template (made from sheet metal or from plastic according to the profile of new, unused tools)
    • the dividing bar will secure the precision of the pitch
    • using the feed thumb grabbing the tooth is unsuitable
  2. the teeth must not have a blue color (effect of thermal acting)
  3. the tips of the teeth must be in line
    • deviations are measured using a straight edge ruler and a drift meter
  4. during precise sharpening the grinding disc must hold with the side edge of the blade an angle of 90°
    • inspection with a square
  5. the axis of the grinding disc must be above the middle of the thickness of the saw blade and the blade must be clamped precisely vertical
    • inspection with a ruler and a slide cage
  6. the thickness of the removed layer during a single pass is to be between 0.05 mm – 0.1 mm while grinding wihtout the use of cooling, it is possible to remove a greater layer in a cooled system
    • the blade is reground at least 4x
    • the thickness of the removed metal must not be so great as to cause colored areas on the face or on the back of the tooth
    • before the end of the sharpening it is recommended to let the last pass of the sharpener go freely (just to clean off), without the adding of layer
    • if a needle is occurring even during a small removal, then it is necessary to clean the disc or to selected a disk with a different grain
  7. the area of the grinding disc must hold with the face of the teeth of the angle of 2° - 5°
    • inspection by straight edge ruler, angle gauge
  8. if a colored layer occurs, and it is necessary to sharpen for as long as it takes until this layer is totally removed
  9. it is necessary to pay attention so that the radius of the rounding of tooth corresponds to the original profile of tool
    • a too small of a radius causes the risk of the occurrence of cracks, which confined the lead to the tearing of the saw blade
    • select the thickness of a disk according to the radius of the foot radius:
    Radii of the foot radius for the most used pitch
    Pitch of the teeth Radius of the foot radius Thickness of the grinding disk
    22 mm R4.4 8 mm
    25 mm R5.0 10 mm
    26 mm R5.2 10 mm
    30 mm R6.0 12 mm
  10. During alternating skewed sharpening the angle of the face of the skewed grinding must be the same on both of the sides
    • inspection using an angle gauge

Method of Sharpening

skewed sharpening is only possible on set teeth


Straight sharpening

Skewed sharpening

Sharpening RP with Set Teeth and RP with Beetled Teeth

As a rule of the sharpening is performed on a set saw, not the other way around. If an already sharpened saw was to be set, then in the first place the cutting angles on the teeth would change and the saw will have the tendency to run in and there's also the risk of injury to the operators of the grinding shop during the setting of the sharp teeth. After sharpening the setting is only inspected and possibly gently adjusted.

During the grinding of set or beetled RP blades it is suitable to use a disk with a medium to light grain.
Cooling is not necessary but it is suitable.

Sharpening RP with Stelitte-Tipped Teeth

For the sharpening of PR blades with stelitte-tipped teeth it is suitable to use a disk with fine to a very fine grain.

Cooling during the grinding of stelitte-tipped teeth is greatly recommended (longer lifespan of the disc, better quality of the ground area, the removal of the stelitte grinding powder by the fluid, ...).

Stelitte saws are very susceptible to instability during greater deviations in grinding. It is necessary to secure that the edge of the tool is almost absolutely (± 1°) vertical to the side edge of the saw. A deviation of 2-3 angle degrees will already cause, during higher cutting speeds, the bending of the blade in the cut and quicker wear of the tool (only one tip of the edge is stressed).

It is necessary to sharpen all of the teeth - therefore in the case, that sets or combinations of stelitte-tipped and non-stelitte-tipped teeth appear on the saw toothing. It is ideal to grind the entire profile of the tooth, because this will maintain constant cutting conditions for the entire lifespan of the weld-on.

Cooling During Sharpening

The tool - saw blade - heats up significantly during grinding (depends on the removal, the temperature can reach maximums of up to 1000°C). During excessive heating, there occurs in the area of grinding a very hard (hardened surface) layer (about 0.2 mm, it exhibits itself as a change of color - into blue through purple all the way to back), which even though it is very hard it is also very fragile and can lead to the cracking of the tool in the foot radius of the tooth and finally result in the tearing of the entire saw. This same layer which occurs on the tooth results in the tooth's quicker dulling (because it easily breaks off due to its fragileness) and with that an obviously lower economical cutting effect.

Cooling during grinding prevents this, because the fluid takes away the heat (and also scale) from the area of grinding. If cooling is available, then it is necessary to secure its continuousness (it must not be interrupted), output (current) and evenness.

Generally if it is not possible to secure this (mainly continuousness), then it is better to work without cooling and eliminates overheating by lowering of the removal from the tooth, correcting the movement speed, adjust the throwing of the grinding disk, lowering its revolutions if it is possible or its replacement with another, with a different grain.

Errors Caused by Improper Sharpening and Their Removal

Defect Cause Consequence Repair
Excessively small radius of rounding of the gap
Too little rounded profile of the disk, thin disk The saw dust has a hard time falling out, run in during greater feed speed A higher disk thickness, lower the lift of the feed finger, round off the profile of the disk
Excessively high tooth height
Incorrect adjustment of the sharpener Too small an angle of the edge, low stability of tooth during cutting, short duration of sharpness and setting, run in, wave shaped cut Use templates for the inspection of the teeth profiles
Small tooth height
Incorrect adjustment of the sharpener Small tooth gap, run in during a larger feed speed Use templates for the inspection of the teeth profiles
Uneven tooth height
The middle of the disk is not exactly above the center of the thickness of the blade, a play in the bearing and in the disk guide, the blade is not guided properly, the edge of the feed finger is not perpendicular to the saw blade or it is worn Uneven loading of the teeth, quicker dulling, worsened quality of the cutting area, run in during higher feed speed, uneven widening of tips for beetled teeth Inspect the plumb with a square, drift meter, inspect the cutting edge with a ruler
Bowed cutting edge
The guiding bar is not properly attached to the machine, the ends of the blade are ground down more than the center (as a result of the weight of the blade) Uneven loading of the teeth during cutting; worsened quality of the surface Attach according to level, inspect the cutting edge with a second ruler
Dipped cutting edge
The guiding bar is worn under the grinding disk (grinding dust), the ends of the saw blade are less sharpened than the center Uneven loading of the teeth during cutting; worsened quality of the surface After removing the defect, clean until dry, do not oil, inspect the cutting edge with a long ruler
Colored tooth tips
The grinding disk is removing an excessively thick layer of metal, an excessively high surface speed of the disk, the disk is too hard The tip of the tooth is fragile, under the fragile layer there is a tempered layer with a lower resistance, fast dulling, worsening of the surface, run in Remove the causes
Non-precise sharpening, part of the teeth are colored
The feeding finger grabs in the area of the rounding of the gap, the vibration of the saw blade, a play in the bearing, guiding See the preceding case, uneven height, pitch Adjust the feeding finger so that it grabs in the upper third of the tooth height
Uneven pitch of the teeth
The last tooth was ground too much during its manual sharpening, the last tooth is either not at all sharpened or very little sharpened (during the grabbing of the feeding finger by the second tooth); unevenness on the area of the blade, the guiding bar is in a bad shape Uneven loading of the teeth in the cut; uneven widening of beetled teeth, worsened quality of the surface cut, run in of the blade in the cut Inspect the pitch and the profiles of the teeth with a template, remove the causes
Incorrectly sharpened teeth, tips turn blue

The disk does not have a deviance of 2° - 5° from the direction of movement (face angle) Rough cutting area, run in Inspect and configure the disk's tilt-angle
Improperly ground stelitte weld-on
The grinding disk is not in the 90° angle with the side of the blade; the disk is not precisely above the center of the thickness of the blade During a deflection angle of the edge larger than 1° and higher feed speeds there is a strong tendency the run in of the blade, quicker dulling (one tip of the edge dulls faster) Straighten the grinder's spindle, have the grinder adjusted by a professional, inspect with an optical angle gauge, if it is available
 
 


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