I thought this was a brilliant idea, but it failed completely. Why?
I opened a digital micrometer to 4" and clamped the two ends to a band saw
blade. I then tensioned the blade. I figured the micrometer jaws would be
pulled apart a few thousanths and I could determine the tension.
Nothing happened. I flipped the tension lever back and fourth, but it stood
relentlessly at 4". The ends were clamped securely and the micrometer took
very little force to move, so I don't think they were just slipping.
Shouldn't this work, or at least do something?
I hope so. I have the indicator set to 3/4". With the lever in one
position the blade is floppy; in the other it is taut. That's right isn't
it? Hey, I just bought the saw last week; I don't discount the possibility
that I don't know what I am doing.
Not to hijack this thread or anything, but I'd like very much to try
this with a dial indicator. You don't have a reference for the stretch
properties of the various metals for bandsaw blades, do you?
I'm using timberwolf silicon steel blades, but I didn't read anything on
this in the Suffolk brochure...
For my MM 16" saw I used a dial indicator with mounts about 12" apart. The
calculations are straight forward (I posted the process w/pictures on the
yahoo MM group several years ago). I don't remember exactly, but it was
somewhere about 0.003" to tension a 1" blade and my indicator was graduated
such that a full revolution is 0.004".
You really need a sensitive instrument to tension a blade especially if your
mount points are only 6" apart.
I would have thought that an old musician like you would have used the
"tuning fork method".
You can look it up.
When it first came out it didn't make a lot of sense for guys who
couldn't hear different notes, but in an age where a tuning checker
can be had for twenty bucks it might make sense to tune a bandsaw
blade according to the note it makes when plucked.
tjwatson1ATcomcastDOTnet (real email)
I've "plucked" on it for years, hell even executed a mean harp gliss on the
damn thing a time or two, but the old tension spring was shot to hell, so
even under full compression it was about 1/5th of the needed compression for
the size blade ... basically it would pluck the same old tune, but more than
a few octaves too low.
What a difference with the new tension spring ... now it really sings. ;)
I've seen this method written up before. In principle, it should work,
but you're looking for only a few thousandths of an inch of stretch.
Might be close to the limit of resolution of your measuring device.
ok.. I guess it's better to ask a dumb question that make a dumb mistake...
Before measuring stretch and deflection, should the blade be at some preset
tightness or something?
Opps.. sorry, tightness wasn't listed, maybe preset tension?
Maybe I'm just not seeing something here, but if I take my cheap chi-wan-ese saw
and loosen the tensioning knob 5 turns would I get the same results from this
test as if I'd tightened it 5 turns instead?
I'd be very dubious of any results you would get if you could even get this
to work. The amount of error in your measurement is bound to be a large
percentage of the measurement, which means your calculated readings would be
all over the map if you factored in measurement error.
The really cool way to do this would be with a strain gage. Glue it on,
load it up to a predetermined change in resistance, and voila.
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