Bandsaw blade tightness?

dale71 · Sep 21, 2010

How do you tell if a bandsaw blade is tensioned too tight or not tight enough? How does everyone tension their blades?
Thanks in advance.

Ries · Sep 21, 2010

If you are talking about a small bandsaw, up to 12" or 14" or so, most likely you cant get it tight enough.
Somebody used a tension gage, and found that the most tension it was possible to put on a 4x6" horizontal bandsaw by tightening the plastic knob by hand was about half of what the recommended tension should be.

If its a real industrial machine, like a Do-all or a Grob or something, it may be possible to tighten it sufficiently, but most people still leave em too loose.

Big saws often have tension gages built in.

You can buy a tension gage to check any saw blade with, but they arent cheap.

Ray Behner · Sep 21, 2010

Yup, they're not cheap. I paid over 300 bucks for mine fifteen years ago. But, if you know someone that has one, have him guage your blade to proper tightness and you'll roughly know where to crank the handle. 30,000 pounds is correct for mine. I think that's standard for 1''.

On edit: You may not want to tighten it that much on a Chinese saw.

67Cuda · Sep 21, 2010

I tighten them until I get a nice little twang when I pluck it. No need for a gauge.

Tom

Michael Moore · Sep 21, 2010

Tom, is that a Duane Eddy twang or a Nashville twang?

cheers,
Michael

A_Pmech · Sep 21, 2010

Fellow blade plucker here.

I've learned by trial-and-error what the correct tone is for various blade widths.

I'm not a musician my any stretch, so I can't tell you what note.

This calculator and tone generator is rather interesting and may be of use to you:

Thien Audible Tension Gauge for Bandsaws

HuFlungDung · Sep 21, 2010

That Thien Audible Tension Gauge is cool. I've only tightened my bandsaw by ear over the years, and it seems to turn out pretty close to what his sound samples compute to for my saw.

Really, the reason I tighten the snot out of my bandsaw tensioner is to keep the blade from popping off the drive wheel when the going gets a little bit tough. Any less than 30,000 psi (approx) is too loose for my saw. I run plain old flat steel wheels, no tire of any description on them.

Ken hosford · Sep 21, 2010

Band saw blade tention

Interesting phenomena Saw with rotating axles will fatigue there axles with over tension , saws with fixed axles just bow or bend there frames . I saw the saw at work bust it's axle from over tension .

dale71 · Sep 21, 2010

A_Pmech said:
Fellow blade plucker here.

I've learned by trial-and-error what the correct tone is for various blade widths.

I'm not a musician my any stretch, so I can't tell you what note.

This calculator and tone generator is rather interesting and may be of use to you:

Thien Audible Tension Gauge for Bandsaws

Wow! That's how I go, by plucking it. Just didn't know what frequency. I thought if I asked about plucking it here on this forum, someone would think I'm crazy! Ya ain't got a geetar ya got a bandsaw! I will have to fill in the blanks and see what the frequency is in the morning. It's a 1/2" saw, imports, done a lot of cutting in 25 years though. Other saw is a 3/4" blade. Like Ray said in the above post, being they're imports, I won't take it to the extreme, don't want a broken bandsaw, but I don't think I am getting them as tight as they should be.

Guest · Sep 21, 2010

On my horizontal with a 12 foot long 1" wide blade I turn the tension knob stem with vice grips with one hand till I almost can't turn it anymore. I haven't snapped a blade or burnt any bearings, any looser than that it will jump off when the blade gets dull. So on mine it can never be too tight.

Forrest Addy · Sep 21, 2010

A tension gage is a nice to have but they are expensive. I was thinking a guy could home-brew one from a sensitive dial inidicator registering motion in a gage length of the saw band. If saw bands are to be tensioned from 30,000 to 60,000 PSI and the Young's modulus of steel is 30,000,000 then a gage working over a span of say 5" would show 0.005 to 0.010 stretch; should be duck soup. This will work on any blade of any width and thickness. Since it detects stretch only the band section drops out of the picture.

How hard could it be: an indicator, two clamps, a frame dealie. Or reverse engineer a factory one.

If you're musical and have a pitch pipe handy the twang method might be pretty accurate if done on the idle side of the band. The guides etc are seldom in the same place for every band change and because of the loose contact in the guides the musical tone may be entirely damped out.

I give the band a tug sideways as I tension it letting many years of tweaking bandsaws speak through my fingers. Not much help to a noob, am I.

PaulM · Sep 22, 2010

Maybe these would work?

HMC Int'l.; KRIKIT TENSION TESTERS

They are designed for testing v and ribbed belt tension, the small versions are available from NAPA stores (NBH KR1, and NBH KR2), if you need the one that can go to 700lbs I did not find it on the NAPA web site, looks like you would need to order it.

Paul

wippin' boy · Sep 22, 2010

i tighten mine till my eyes bulge out

rons · Sep 22, 2010

dale71 said:
How does everyone tension their blades?
Thanks in advance.

Adjust tension by sound:

Slowly increase tension while plucking the back of the blade. A musical note
like that of a guitar string will be heard. A narrow blade will have a high pitch
and a wide blade will be more bass-note like. As the tension is increased the
sound will become less flat. You are looking for the point where as you tighten
the sound will decrease because the blade is not vibrating as much.

Adjust tension by blade deflection:

Using side pressure the deflection is measure by eye or a tension gauge.
A moderate force on the blade will deflect a blade and you can judge the
right amount after practice like the sound method.

I always remove the tension a bit after use.

Peter Miles · Sep 22, 2010

I have a copyright 1943, Tenth Edition, hardcover copy of the Doall Contour Saws book (which is within a year or two of the age of my DoAll, coincidentally).

On pages 18-19, it has a two-paragraph section entitled Tension of the Blade. This states:

There is no hard and fast rule by which the correct blade tension can be obtained. In general, tighten new band saws just enough to do the work without twisting or wandering in the cut. After they have been used a little they will have stretched slightly. Then readjust the tension to take up this slack. Blades 3/16" or less require less tension than 1/4" or 3/8" blades. This is due to the fact that narrow blades have less metal in them and require less tension to hold them in line while cutting is being done. Too strong tension, which is unnecessary, will wear the rubber wheel tires.

Correct tension on the saw blade can only be applied through experience on the part of the operator. It is better to err on the side of too little tension than too much, since heavy tension is detrimental to the bearings, the band saw and the wheel tires.

I'll have to check my other, newer DoAll book to see if they have any more precise guidance.

Steve in SoCal · Sep 22, 2010

The dial on the left.

I too run the bands a little loose for most work, if I am cutting something thick I will tension the blade up. I also reduce the tension on the band after I have made a cut with it tensioned to high C.

Steve

Jeff · Sep 22, 2010

Forest, there were plans for something like that in Fine Woodworking magazine several years ago. They were talking about wood saws, but should still apply, I would think. Some googling might turn it up.

David Utidjian · Sep 22, 2010

I have a fancy-shmancy belt tensioning gage that I bought 25 years ago for tensioning the timing belts on Porsche 928 and 944 models. It cost me $500 back then. It uses the deflection principle for determining correct tension (see pics). I also got the calibration attachment. I suppose that one could make up a similar gage for tensioning of steel bandsaw blades. It could even be a "product" with a ready market of "gentleman woodworkers" that seem to have more dollars then sense when it comes to shiny gadgets for the workshop.

67Cuda · Sep 22, 2010

Steve in SoCal said:
The dial on the left.

I too run the bands a little loose for most work, if I am cutting something thick I will tension the blade up. I also reduce the tension on the band after I have made a cut with it tensioned to high C.

Steve

Ya Steve, whatever, you just wanted to show off that nice looking DoAll. :drool5:

Tom

PaulM · Sep 23, 2010

Hey David - I have the same gauge, which is also what led me to the Kriket gauges. I figure you could probably calibrate the Porsche gauge to use it on a band saw but no one would have one and the cost is fairly high, so the Kriket gauges seem to be a low cost option that could work.

Paul

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