Bandsaw tensioning

[eganders]

I saw a video and article about the inexpensive tension gauge for the bandsaw from John White in Fine Woodworking. I thought it was a great idea, but since I have a number of dial and digital calipers, I thought I would use a 6 inch caliper set with the jaws 5 inches apart. I clamped the jaws to the blade just as he did his jig. I put some tension on the 1/2 inch Suffolk Timberwolf blade just as he did and set the dial to 0. I then started to crank tension on the blade.

I have no doubt that the standard spring is weak, but I don't see really ANY MOVEMENT AT ALL from the caliper. I can't believe the tension that I will need to get the recommended 15,000 psi. I will collapse the spring and THEN some. I can't bring myself to put the tension on the blade that would bring the 2.5 mils of displacement on the caliper to get the 15,000 psi. Without some more confidence that I am going the right way, I am afraid I will break the saw (and I will be WAY past collapse of the spring). Can anyone tell me what I am doing wrong? Has anyone done this and can tell me what did your standard Delta gauge read (with the standard Delta spring) when you put 15,000 (or whatever PSI you used)?

By the way, I know about all the different methods, such as the flutter test, etc. I am doing this to get a feeling what a standard tension is and then I will go my own way, but I would like to at least experience what 15,000 psi is.

[Leon]

Some springs are not up to the challenge or have no longer go their original tension. This could be why yours collapses. More than likely your blade would break before your saw would.

[eganders]

Maybe the blade would break, maybe not...how should I know... I sure as hell don't want to find out.

BUT, I want experiences from people that have really TRIED this. Has anyone measured the true tension on a Delta saw with a strain gauge mechanism, calipers, shop made jig or some other scientific method and can relate their ACTUAL experiences??? Does the standard Delta spring collapse or not at 15,000 psi??

[Swingman]

"eganders" wrote

I use an Iturra bandsaw tension gauge to set my Delta 14", but neither I, nor anyone else, can answer your question with any authority because we don't have your particular spring to test and we would be guessing at best.

Bandsaw tension springs, even when new, can vary as much as 30% in tension pressures.

With the old Delta spring you would be lucky to get 15,000 psi on the Delta

14". But apparently with the newer springs (since circa 2005/6, IIRC), you can, even to the point of exceeding the capacity of your bandsaw, to its detriment.

This is according to the information in Louis Iturra's 2006 catalog.

You might want to call them for a copy ... basically an essential source of information for owners of the Delta and Jet 14" light duty models.

1-866-883-8064

.. and by all means, get some kind of blade tension gauge if you plan on getting the maximum performance out of your light duty bandsaw, particularly when resawing. Not putting the proper tension on the resaw blade is like putting a new set of tires on a racing car and guessing at the tire pressure.

[Leon]

Maybe the blade would break, maybe not...how should I know... I sure as hell don't want to find out.

Well If my saw could not be properly tensioned with out breaking I would want to get a replacement saw, pronto. Which part do you fear will break?

[Frank Boettcher]

Good point. At that point for sure and even prior to that point, other things start to give. For instance, at the time of the change mentioned above, one of the things measured was the deflection of the overarm to determine if the whole package would work. Like any mechanical device, just adding a tougher component (spring, HP of motor, wider blade, etc.) will only get you so far and then the weakest link limits.

FYI, at the time of those changes, actually a little earlier than you stated, the domestic Delta overarm had the least deflection when tested against the imported units, competitor or Delta. Don't know how they would stack up presently.

Frank

[Nova]

If 15,000 PSI is the recommended tension (I can find no such listing on Suffolk's site) it "Pounds Per Square Inch". You're dealing with a blade that has a cross section of .5" x .025" or .0125 sq. in..

[eganders]

In thinking about this further, I may change direction....

How do you make a strain gauge device that measures the strain (change in length) of a bandsaw by clamping the gauge device onto the metal band. The gauge would be an analog bridge strain gauge that would have to have pads that allow them to be clamped on the metal band, but the material that the gauge device was made of would have to have little effect on the total resistance to elongation of the band, since the band strain vs. force is what is being measured.

I know I could glue a strain gauge on the band itself to do the measurement, but I want to be able to mount and unmount the strain gauge on different bands.

Yes, I could buy a mechanical strain gauge to do the measurement, but find that I can buy a used strain gauge meter for much less and if I can make a gauge, I will have a strain gauge meter for use in other applications. Also, I believe it could potentially be more accurate also.

Any ideas?

[Swingman]

"eganders" wrote

Check this out:

[Ken]

The Suffolk Timberwolf blade is designed as a low tension blade, I use it resaw with, not a good blade for your test. Pick and Olson or something else, this blade is to easy to set up and easy on your saw, (low tension) you're going to collapse a wheel at such high tension on a old saw. My $.02 Ken

[eganders]

I used that approach (see my 1st post), but I did neglect to try something. I did the same thing with a 6 inch dial caliper, but my digital caliper does go down to .01 mm. It may not be super accurate, but it is more precise than my dial caliper. I can get about .03 mm over a

127 mm (5 inch) range, so I get about 7 KPSI. That is pretty good and maybe good enough for what I am after.

[Bruce]

On Tue, 8 Apr 2008 18:06:49 -0600, eganders wrote (in article ):

I used a dial gauge with 0.0001" resolution over 10" of blade span. It worked well, but I really doubt something with 0.001 resolution would be 'accurate' but it could be 'good enough'. I'd do your measurement, strip down your setup, then repeat several times to see your measurement variance (then average).

-Bruce