Bandsaw ate itself?!

I have a grizzly 18" bandsaw, I strung up a 1" resaw blade on it today, was resawing some flame maple, and the BACK of the blade cut right through the metal guide block holder!
http://asmhacker.org/bandsawfork.jpg
has this happened to anyone else? What did I do wrong?
I called grizzly, the part is only $4 to replace, so I bought two :P
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What about the rear thrust bearing? Was it touching the blade? Is it even installed?

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As far as I can tell, there are only two thrust bearings, one on the guides above the table and one on the guides below, and they both contact the side of the blade. A quick peek at the parts list and exploded diagram seems to confirm this. Am I missing something?
On Sun, 25 Jan 2004 02:48:02 +0000, MSgeek wrote:

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They should barely (dollar bill thickness) almost be touching the back of the blade.
When the saw is on and not cutting they should not spin. When the saw is cutting they should be spinning. They support the rear of the blade. What model is the saw?

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Ah, I see... I had the thrust bearings against the *side* of the blade, but it makes more sense against the back. The thrust bearing supports the rear, not the guide block holder....
forgive me, i'm learning :) Fortunately, it was a relatively inexpensive mistake.
It's a G1012, btw
On Sun, 25 Jan 2004 03:39:14 +0000, MSgeek wrote:

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No problem! Yes that was it. Yes it was inexpenisve. BTW what blades are you running?

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Whatever I can find hanging on the wall :)
We have two bandsaws, one's an old packard precision 14", that's not operational for whatever reason, and we have this big grizzly 18" that we actually use. It normally spends its days with a tiny 1/16" blade on it, but I really wanted to resaw some tiger maple that I bought and bookmatch it, so I dug through the pile of blades on the wall and found a nice 1" hook tooth blade and put it on. I managed to get the resaw I wanted done just as the guide block holder fell in half :P I have no clue what brand blade it is, but I could take a picture of it for you :) There are a bunch of blades out there, some are small, for the packard I guess, and there's a few of the big 124" blades that the grizzly takes.
Fortunately, grizzly's already shipping me a new guide block holder, as well as some spare blocks, since it's missing two on the bottom guide.
(hm, come to think of it, there's a metal bandsaw back in the back of the shop under a pile of junk and dust, one of the ones where you can tilt the blade horizontal if you want. I should pull that thing out and see what it can do)
On Sun, 25 Jan 2004 06:39:52 +0000, MSgeek wrote:

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Would guess the blade was WAY under tensioned, and as you re-sawed the blade bowed BACK into the and rubbed it away
Not sure what the specs on that specific blade are, but would bet it wants to be around 20,000-30,000 psi tension which is pretty hard to achieve on many saws
John

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Perhaps a silly question, but how does abandsaw tell you "please, no more tension!"
Is the knob just too hard to turn? Snap the casting? The body flexes visibly?
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Stephen Meier asks:

Yes, to all 3, but let's hope your first one actually comes first. After a bit, too, you get used to plinking the thing with a fingernail to check tension. Supposedly, you can also use a tuning fork, but I'm tone deaf.
Charlie Self "Character is much easier kept than recovered." Thomas Paine
http://hometown.aol.com/charliediy/myhomepage/business.html
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Charlie Self wrote:

I can't see how a tuning fork would help much unless you know what note you're aiming for, and I would well expect that the target note is going to vary with the thickness, width and other qualities of the blade. Maybe I'm missing the point, and the objective is to get every blade, no matter the type, to plink the same?
Not that I have a bandsaw anyway, mind you. Well, not a woodworking bandsaw. The rule I use on my metal cutter is when I can't turn the knob any further without some sort of cheater, it's tight enough.
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On Sun, 25 Jan 2004 20:45:20 -0500, Silvan

No, rather the opposite.
What you're aiming for is to set tension / area as a constant. Tuning forks measure tension, so you need a different "ping" for each blade width.
The easiest, and most accurate, thing to measure is strain (stretch) which is constant for all blades of the same alloy.
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Use a tension gauge and set it to whatever the blade maker suggests
Other than shorter lifespan of the blade, there is not much really wrong with running a blade with more tension than it actually needs, as long as the saw FRAME will handle the tension, AND you release the tension after use
Also, if you fully compress the blade tension spring, that is a bad idea. Spring completely compressed has NO give to absorb shocks/etc
John
On Sun, 25 Jan 2004 07:29:23 -0500, "Stephen Meier"

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On Sun, 25 Jan 2004 07:29:23 -0500, "Stephen Meier"

It doesn't - the bandsaw ought to cope with more tension than the blade, so for best results ask the blade, not the frame.
A cheap 14" saw ought to tension 1/2" blades and track 3/4" blades. You'll get better results from a 1/2" blade at the right tension than from an under-tensioned 3/4". Fitting a better spring can sometimes help.
To be honest, there is no point in running a blade more than 1/2" wide on a "domestic" 14" saw. You might have to look harder to find the tooth profile you want in a narrower band, especially for huge hook teeth to rip green timber, but it'll work better.
The limit of tensioning a bandsaw is when you bottom out the spring. The frame itself ought to take a huge amount of tension, far more than the blade will ever need, but most 14" machine springs can't tension a 3/4" blade.
With the spring in proper use, it acts as a shock absorber. If you've squashed the spring flat, then there's no "give" in the saw, should the blade catch on anything. The spring rate goes up and so the slightest change in length causes a huge increase in tension - this snaps your blade or damages the wheel bearings.
Blade tension is best measured by measuring length extension (strain) in the blade itself. Strain (length change) is more important than stress (force). Measure this accurately at least once for each blade (redo it as the blades age), then calibrate your own saw for your own favourite blades. Most saws have a tension scale which is inaccurately calibrated, but you can make your own marks on it.
To saw well, we would like to use an enormous tension (force) to stress the blade. However the blade is also a spring, so this applied stress gives rise to a resultant strain (stretching). Too much strain in any steel causes fatigue, and this depends more consistently on the _strain_ achieved, not the stress. We thus reduce the tension on the blade until the strain is reduced enough to give an adequate blade lifetime. Properly run, blades should break from fatigue just as their teeth are worn out.
The simplest strain meter was described in FWW some time back. Take a 6" stick with one end sawn off and sliding loose on a headless nail (effectively a stretchy stick). Take the tension off the blade and clamp the closed-up stick to it at 5" centres. Now tension the blade and watch the gap open up in the stick (You can knock a couple of pins in to give a pair of measuring faces). Measure this gap with feeler gauges. A maximum strain of 0.1% equates to a 5 thou gap over 5" of blade length, which is a reasonable figure.
The pictures are in FWW 147 - Jan/Feb 2001. But ignore the text, because it's ignorant gibberish (You can't measure tension in psi, and it goes downhill from there 8-( )
Some makers (Suffolk's Timberwolf) specialise in blades that are designed to run at a lower strain. Refer to their documentation for advice.
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On Sun, 25 Jan 2004 20:37:49 +0000, Andy Dingley

any chance you could duplicate the setup and post pictures?
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