This report, the second in a two year project to question the existing “rules” for saw designs and real operational limits, investigates three aspects of circular saw performance. The first area of investigation was to determine how operation of new saws in a mill environment changes their cutting behaviour, the second was aimed at determining the operational “sweet-spot” for circular saws of various thicknesses operating at different feedspeeds and finally, the effect of side board stiffness on saw wedging was investigated.
The results from the mill operation portion of the study showed that:
Operation of new saws in a mill did not improve their performance
Tooth geometry errors are a major cause of saw wedging
With the new saws, a strong correlation was found between saw wedging and radial clearance angle differences (error) as well as tangential clearance angle differences.
After operation in the mill, a strong correlation was found between saw wedging and side clearance differences as well as tangential clearance angle differences.
Close attention must be paid to the initial tangential angles ground into new/re-tipped saws to avoid low, negative or unequal tangential angles that cause excessive wedging, particularly as saws are repeatedly sharpened.
The results from the operational “sweet-spot” portion of the study showed that:
Errors in tip geometry are the primary cause of saw wedging. Even as feedspeeds are reduced, wedging can remain high for saws with grinding errors;.
For feedspeeds up to 500 fpm, there was not a significant difference in the wedging between the 60, 70 and 80 plate saws.
For feedspeeds up to 500 fpm, there was only small differences in the top edge standard deviation between the four plate thicknesses
Total Sawing Allowance reduced as saw plate thickness (and kerf) reduced. This should allow for mills to achieve target size reductions, provided machine alignment and cant control are tightly controlled.
The investigation into the effect of side board stiffness showed that:
Wedging increases slightly for sideboards that separated from the base cant due to their lower stiffness vs. those that remained attached