"Jim Wilkins" wrote in message ...

Once I *know* what I want I can machine it, but it appears I don't
understand the subtleties of making a sawmill bandsaw blade continue to
cut straight as it begins to dull.

This clearly explains the problem:
https://woodgears.ca/bandsaw/resaw.html
and this compares a variety of guide designs
https://woodgears.ca/bandsaw/guides.html

The 2-directional curvature of the blade is also the reason why bandsaw
blades and flat leather belts track to the center of crowned pulleys. An
off-center band twists, bends and moves toward the higher side.

His buckling beam model has pinned ends (although the demo doesn't), free to
pass the deflection past the guides to the wheel side. The "beam" ends can't
be fixed because the tooth side which deflects forward out there won't
tolerate running on guide rollers. The guide blocks or rollers can't press
tightly against both sides of the blade due to the sawdust, some of which
can carry around to the infeed guide if the wood is green or pitchy.

On a sawmill the usual answer is to increase tension and offset the blade
downward slightly with the guide rollers to stiffen it. It can't move very
far or the blade will crack.

I was using guides with skate bearings as rollers on one side and fixed
rubbing blocks on the other, and a backing bearing. They worked well with a
sharp blade but deflection started to be a problem once the blade dulled to
half the amount I can tolerate, based on lowered cutting speed. So I cut
wide planks with sharpened blades and then edged them or slabbed logs as the
blade dulled. The salvaged motorcycle's speedometer shows blade speed and
mileage.

The mod I'm designing now is 2" rollers with larger bearings, somewhat
similar to the well regarded Cook's guides but with a backing roller or
washer instead of the integral flange. I design home machinery for easy
maintenance or modification instead of long wear life. Hopefully they will
let the blade tolerate more downward deflection. Before disassembling the
saw last fall I set the guides to barely touch the free-running blade to
record its position for reference.