On 5/21/2020 10:01 AM, Jim Wilkins wrote:
When I built my sawmill I used the ball bearing blade guide design of my
Delta 4" x 6" metal cutting bandsaw, which has proven less than ideal on
the sawmill, so I'm looking for alternatives. These appear to be popular:
http://cookssaw.com/standard-roller-guide-assembly/

As I understand it, they should be positioned to lower the blade 1/8" to
1/4" below its free position to help it resist twisting in the cut. It
concerns me that the blade back rests on and rubs the flange rather than
a separate ball bearing. Does anyone have experience with operating and
maintaining a bandsaw lumber mill?


I don't , but from what I've seen you post about it would seem
trivial for you to design a guide with the features you want ... Use
that basic design you posted the link to , but replace the flange with a
ball bearing . I'm thinking something like a scaled up 4x6 guide with 2
bearings per side in a sleeve roller and a back bearing , single but
also sleeved . Maybe use 4140 for the rollers .
--
Snag
Yes , I'm old
and crotchety - and armed .
Get outta my woods !

"Snag" wrote in message ...

On 5/21/2020 10:01 AM, Jim Wilkins wrote:
When I built my sawmill I used the ball bearing blade guide design of my
Delta 4" x 6" metal cutting bandsaw, which has proven less than ideal on
the sawmill, so I'm looking for alternatives. These appear to be popular:
http://cookssaw.com/standard-roller-guide-assembly/

As I understand it, they should be positioned to lower the blade 1/8" to
1/4" below its free position to help it resist twisting in the cut. It
concerns me that the blade back rests on and rubs the flange rather than a
separate ball bearing. Does anyone have experience with operating and
maintaining a bandsaw lumber mill?


I don't , but from what I've seen you post about it would seem
trivial for you to design a guide with the features you want ... Use
that basic design you posted the link to , but replace the flange with a
ball bearing . I'm thinking something like a scaled up 4x6 guide with 2
bearings per side in a sleeve roller and a back bearing , single but
also sleeved . Maybe use 4140 for the rollers .
--
Snag

=======================================

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.

Neither do they:
https://forestryforum.com/board/inde...topic=86772.40
https://sawmillcreek.org/showthread....while-resawing
"It takes a fair amount of development of personal skill to learn how to get
the best results from a bandsaw."

"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.

On Sat, 23 May 2020 09:31:05 -0400, Jim Wilkins wrote:
"Jim Wilkins" wrote in message ...
[...]
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. [...]

With a reasonably fast micro, eg Raspberry Pi4, and an ok camera attached
to it, plus a bunch of controlled motors and attached mechanisms, it's
feasible nowadays to make an active sharpener, to touch up the teeth while
the bandsaw is running. Feasible means possible to do; it doesn't mean
easy. It would be a project that could last a few years longer than
the several days of work your larger-bearings approach will take, and
could cost a couple of magnitudes more dollars, depending on how many
sawmills got wrecked during development.

--
jiw

"James Waldby" wrote in message ...

On Sat, 23 May 2020 09:31:05 -0400, Jim Wilkins wrote:
"Jim Wilkins" wrote in message ...
[...]
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. [...]

With a reasonably fast micro, eg Raspberry Pi4, and an ok camera attached
to it, plus a bunch of controlled motors and attached mechanisms, it's
feasible nowadays to make an active sharpener, to touch up the teeth while
the bandsaw is running. Feasible means possible to do; it doesn't mean
easy. It would be a project that could last a few years longer than
the several days of work your larger-bearings approach will take, and
could cost a couple of magnitudes more dollars, depending on how many
sawmills got wrecked during development.
--
jiw
================================================== =====
The blade runs at 45-50MPH and I don't know nearly enough about servo loop
math to tackle a project like that. I had enough trouble programming an
open-loop routine that stepped a drum printer head in the short gap between
the end of row N and the start of N+1 with approximately critical damping
(no overshoot).

The blades can be sharpened with grinding wheels contoured to the gullet
geometry:
https://woodmizer.com/Store/Product/Index?id=3648

"James Waldby" wrote in message ...

Feasible means possible to do; it doesn't mean easy.

=============================================
Or it means some dreamer thinks it -may- be possible.

Sometimes I/we could make it work, sometimes not. I had fun trying.

"James Waldby" wrote in message ...


With a reasonably fast micro, eg Raspberry Pi4, and an ok camera attached
to it, plus a bunch of controlled motors and attached mechanisms, it's
feasible nowadays to make an active sharpener, to touch up the teeth while
the bandsaw is running. Feasible means possible to do; it doesn't mean
easy. It would be a project that could last a few years longer than
the several days of work your larger-bearings approach will take, and
could cost a couple of magnitudes more dollars, depending on how many
sawmills got wrecked during development.
--
jiw

================================

Feasible perhaps, also risible.

The blade maker suggested and sent me a short piece of blade to use to
design a cam that would guide a small cylindrical grinding stone along the
gullet path, one tooth space at a time. The stone could be any size up to
the gullet radius as long as the cam follower pin is the same. This reduces
the tooth grinder to a fairly simple Dremel attachment and the blade guide
to a slot with an index pin.