Apparently, I have been applying way too little tension on my blades. Now I
have a much better idea of where I should be w/ tension.
(I was never a big fan of the pluck and listen for a tone technique.)
I inherited an expensive bandsaw tension gauge many years ago and realized
then that, at least on my bandsaw, the factory marks were way too low also.
Makes a big difference when using the proper tension, so a gauge is a must
if you want to get the best out of some of the older bandsaws, and this is
an affordable way to go about it.
On 10/28/2012 7:33 AM, email@example.com wrote:
Good information and findings but how about a tension warning indicator
that lets you know when to retention during sawing operation. When the
blade warms up from simply spinning it will stretch, more when cutting,
and then less when not cutting.
While we all would like to be able to narrow this down to an exact
science temperature changes every thing.
On my saw the tension gauge is on the exterior in plain site while
cutting. Most saws require you to turn off the saw and open up the
wheel cover to recheck tension. I find it quite common to have to
retention considerably after only a few minutes of sawing and after a
few minutes of cooling down the blade is over tensioned.
Something to think about.
On 10/28/2012 9:41 AM, firstname.lastname@example.org wrote:
of temperature. How about an internal blade cooling system that maintains 25 C?
Ok I have the solution. On a saw with the typical pointer indicating
tension you mount a mercury switch. 3 wire mercury switch. When the
pointer moves one direction as the blade warms up the switch tilts and a
tension motor begins to increase tension until the mercury switch is
again in a neutral position. As the blade cools and the pointer moves
in the opposite direction the switch indicates to loosen tension.
You zero the mercury switch when you initially adjust the blade tension.
What could be more simple? :~)
Yep, making it more important to be properly tensioned to start with.
Figuring that industries relying on the bandsaw would be addressing that as
a concern, this is an interesting read on the subject, which also raises
the question, how do you put a "back-crown" on a bandsaw blade?
Best I can translate the jargon, their concern was that the toothed
edge of the blade expanded from friction heat, effectively reducing
the tension on the front blade edge. To maintain uniform blade tension
at operating temperature, I think they are suggesting that the rear
edge should be longer than the front.
I may have some OCD tendencies, but such concerns too over the top to
be helpful in my shop.
No shit ... ;)
You'd have to have a big honking blade to just "increase the tension to
the tooth edge" of the blade, or some such words.
That said, I do agree that the most heat would be generated at the tooth
edge, and the wider the blade, the more heat dissipation toward the back
would occur, with less loss of blade tension.
IOW, use the widest blade possible, consistent with the task, and it
shouldn't be a big factor on whether the cows made it home.
On 10/30/2012 12:05 PM, email@example.com wrote:
Can you name a brand that has a properly designed tension spring? Not
the case on my Laguna LT16HD.
And since tension is increased with the compression of the tension
spring, how would a properly designed spring maintain the proper tension
as it decompresses when the blade stretches?
I'm not familiar with enough bandsaws to know if any have a tension spring
that does this well.
A long enough tension spring would change its length by a small enough %
that the force it exerts would be close to constant.
Are you guys bottom posting... after all the hell you gave us, now you
are guilty of this....hmmmmm.
A spring can be built to properly maintain tension. just like motorcycle
springs, where you have springs inside of springs (coils with inner
coils). The higher end springs for racing maintain almost constant
tension so the bike tracks the same no matter what.
Maintaining constant tension is not the problem, as you said this has
been acomplished in the transportation industry.
The trick is to have a spring maintain constant tension with limitless
possible initial settings.
On Sun, 28 Oct 2012 05:33:31 -0700 (PDT), firstname.lastname@example.org
FWIW, you will hear a lot of different thoughts on blade tension and
the proper setting. One thing to bear in mind is that the right blade
can affect how much tension you need. Too much sawdust caught in the
gullets will force the blade to shift off line and cause rough cuts.
Lower feed rates can help, but a 3 TPI blade has been recommended as a
good blade and I have found it works well for me. Given that, you can
use a lower tension and get good results, even in a wide resaw.
The benefit to your saw is less stress on the frame and less stress on
Fine Woodworking has some info presented by Michael Fortune that
suggests all this and also has tips to adjust blade tracking to
correct for drift. If you think about it, having the blade slightly
forward or slightly back of the top of the crown on the wheel will
cause the blade to twist. That causes drift.
Using the adjust blade tracking technique means you don't need to
adjust the fence to compensate for drift.
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