measuring BS tension with a micrometer?

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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?
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Toller wrote:

Yes, and in fact FWW had an article on a tensiometer based on similar technique (except they used feeler gauges).
Are you sure you were tensioning the blade properly?
Chris
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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.
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The article indicates that over a 5" length (open the calipers to 5") the blade should stretch .001" per 6000 psi tension. Therefore a properly tensioned blade should read about .003".
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enough to do the job. Maybe it has more resistance than I think.
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Toller wrote:

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...
er
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On Mon, 3 Apr 2006 11:29:16 -0600, Toller wrote

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.
-Bruce
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Recently 'inherited' an Iturra "Blade Gage" which works on the same principle.
Made me immediately upgrade the tension spring in my US Delta 14" bandsaw.
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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.
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Tom Watson
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"Tom Watson" wrote in message "Swingman" wrote:

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. ;)
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I think I got plucked when I bought my saw.. *g*
Mac
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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.
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I can assure you it will work, at least with a dial indicator and probe.
and the winner is?
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So you are measuring stretch? What if you apply a deflection?
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On 4 Apr 2006 02:23:06 GMT, Bruce Barnett

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?
Mac
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Bruce Barnett wrote:

problem with measuring deflection is variation from blade with and tooth pattern. if you measure stretch the only variation you need to account for is steel type, and that difference is tiny.
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Toller wrote:

If you clamp a micrometer spindle it won't turn. Why would you expect the reading to change?
John Martin
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I assumed Toller meant to say he was using calipers, rather than a micrometer.
todd
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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.
todd
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