I saw John Whites shopmade tenson gauge and a discussion elsewhere where a fellow used a dial caliper with its jaws clamped at 5 inches on the bandsaw blade. I tried that method and could hardly get the caliper to indicate any change at all up to the 3/4 inch blade tension on my 14 inch Delta with a 3/8 inch Timberwolf blade. Has anyone tried this? I don’t want to increase the tension any more without feedback from someone. Maybe I am doing something wrong, or does the timberwolf blade have a modulus that may be throwing me off? According to the dial caliper method, I should see about 0.0025 inches of stretch (strain) over 5 inches to get 15,000 PSI of stress. I am afraid I will overstress my bandsaw if I even come close to the 15,000 psi stress.
What has anyone else seen using this method?
Replies
Yup, I've seen both methods with the feeler guage and the calipers. There are a couple of things you are doing wrong right now. First of all, you are using a timberwolf blade. TimberWolf blades are designed to run at low tension. Use the fluttering test to accuaratey set the tension for that blade. Second of all, your saw may not have the proper spring to set that tension. Meaning, the little coil that shrinks when you add tension is probably not appropriate for heavy tension. Therefore, consider upgrading to a Cobra Coil from Carter. It's availible from LV and woodcraft (maybe rockler) and sells for around 20 dollars. After you change these things and you still can't get 15,000 psi, use common sense and use another method (the blade flexing test works well).
Delta factory spring needs to be swapped out with Carter. Delta springs are too weak.
John
I have no doubt that the standard spring is weak, but I don't see really ANY MOVEMENT AT ALL from the caliper. I think I said I had a 3/8 blade. I stand corrected, I put in a 1/2 inch blade. I can't believe the tension that I will need to get the 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. Without some more confidence that I am going the right way, I am afraid I will break the saw.
I'm John White, the guy that designed the original tensioning jig that used the feeler gauges.If you have an older saw, with the original spring, that is the reason that you can't get any measurable tension, they are only capable of achieving about 5,000 psi when they are new and once they have been fully compressed, even once, they will be partially crushed and won't even achieve the 5,000 psi. I had an engineer at a spring manufacturing company analyze the design of these springs and he said they were way undersized if you were trying for 15,000 psi.I discovered all of this when I designed the original jig. I put it on the saw and like you nothing happened. I spent half a day trying to figure out how I had gotten the engineering wrong until I finally discovered the spring problem.Here's my advice, since I have learned a lot more about small band saws since I developed the jig. Put a new heavy duty spring on the saw and then tension it moderately just by feel, crank it up until it has a little bit of flex on it when you press on the side of the blade, while the guides are pulled back, and you will be fine. You can skip the flutter test approach, that method never gives the same tension twice, and I discovered that the flutter came and went with the tracking position not the tension.The big secret to trouble free sawing on a band saw is sharp blades and adjusting the guides properly. 98% of the time when a saw won't cut properly the blade is either dull or is too fine for the thickness of the wood being cut. I have never seen a situation where the tension caused trouble unless the blade was so loose it was almost falling off the wheels.By the way, I discovered the 15,000 psi figure has no rational reasoning behind it. The industry standard for industrial saws, cutting steel not wood, was 30,000 psi. At some point someone wanted a tension figure for the small shop saws and the 15,000 psi figure was simply pulled out of thin air by a tech at a blade manufacture. Nobody ever actually ran tests to determine what the best tension was for smaller saws. My experience is that is that moderate tension, over a wide range, will work fine as long as a sharp blade with the right tooth spacing is on the saw. John White
John,
Thanks for the reply. VERY, VERY interesting. I can relate to the derivation of the 15,000 psi figure. I have had this done in my industries before also. Probably came up with a few seat of the pants derivations myself.
I have seen the replacement springs available from a lot of sources. Since I have the wherewithall to test the tension, I could get one from any source, but do you have a recommendation, or could I just go to my local hardware store and get a heavier duty one with the same dimensions?
The problem with the original springs was that they couldn't get enough steel in the spring to increase it's stiffness, because there is only so much room inside of the housing that holds the spring. The solution was to use a special spring with square instead of round wire. The square cross section is considerably stiffer than a round wire of the same dimension. These springs are used in industry for certain applications, I know of them from seeing them used in the complex mold assemblies for plastic molding. The easiest way to get one is to buy it from a woodworking supplier. I'd recommend getting one from Iturra Design since they pioneered the idea of replacement springs and they are machinists so they know what they are dealing with, and they are just nice people. Amazingly they still don't have a web site. Call them at 904-642-2802.John White
Edited 4/2/2008 8:15 pm ET by JohnWW
"If you have an older saw, with the original spring, that is the reason that you can't get any measurable tension, they are only capable of achieving about 5,000 psi when they are new and once they have been fully compressed, even once, they will be partially crushed and won't even achieve the 5,000 psi. I had an engineer at a spring manufacturing company analyze the design of these springs and he said they were way undersized if you were trying for 15,000 psi."John,
I am confused. If the spring is fully compressed at 5,000 lbs the tensioning rod will continue to apply tension to the blade until the target is reached or the rod / nut fail either by thread stripping or the rod bending or the casting bends or fails. These mechanical failures could occur even with a spring that was not fully compressed.
The intent here is to stretch the blade. That should happen spring or no spring.
The spring would seem to permit gradual increase or decrease of tension and to absorb any shock that could damage the wheel bearings.Don
Once you collapse the spring you certainly can get high tension on the blade by continuing to turn the tensioning knob, but as you noted the spring serves a second function as a shock absorber, so it is not a good practice.John White
John,
I wasn't clear about my confusion.
I read into your response to Eric that you had difficult getting accurate reading from you jig due to the spring being fully compressed.
My thinking is the jig should still measure the blade stretching regardless of the condition of the spring.Don
Don,The jig will measure the tension finally increasing after the weak spring is fully compressed, I did it many times, he just didn't want to do it because he wasn't sure the gauge was reading properly.John White
Eric,
What makes you think you need to torque up to 15,000 psi?
I buy my blades from http://www.woodworkershaven.com/
They have some tips that tell you how to adjust their Viking Blade which is somehow related to the Timberwolf bands.
You should also follow Michael Fortune's tip for bandsaw tuneup found in FWW online.
Although the article discussing being able to calibrate to 15,000 lbs was interesting, I would argue that the blade tension required in any bandsaw is the realm of blade manufacturer. The blade is engineered to operate at maximum efficiency under certain conditions.
Same with the spring. Why is it there - to absorb shock? If so, why change to a spring that hardly compresses and has minimal shock absorbing properties.
Some thoughts.
Don
Edited 4/2/2008 12:06 am ET by Don01
As far as I am concerned the 15,000 psi is a number (although it is a number that many people throw around). All I am interested in is to get some feedback. I get excellent results from apparently much less tension. I just want to have a way to measure and reference other peoples experiences and know what certain tensions really are.
SO...
The question remains. Has anyone tested tension with a strain gauge mechanism, calipers, shop made jig, or some other scientific method and can relate tension in PSI to the reading on a delta gauge with the STANDARD Delta spring......???
On a Jet saw, a real tension gauge proved better than twice the travel indicated by the calibration markings on the saw was required to even approach 10,000 psi tensioning.
Well, one thing I am learning here (and education and a reference point is what I was after anyway) is that I don't want to put anywhere NEAR the levels of force that you typically hear. I have gotten excellent results from the tension I have, and I can't EVEN MEASURE IT it is so low!! I still wish I could make a reading of the true stress level, but I am not going to do it with my caliper method.
I could create a lever arm arrangement that would multiply the small stress I am getting by 3 to 10 times and I might see some movement then. I wonder if there is any other way. Keep in mind, I am still just trying to educate myself as to what the level really is. As a woodworker, I am satisfied that I can come up with a level of stress that is acceptable and repeat it pretty closely with the existing spring in the saw.
Eric,
To measure tension and quality of cut comparisons, you would need to make test cuts at various settings, which makes it very difficult to attach a measuring device to the blade.
Wild guess here. Could you not place a small hydraulic ram between the casting and the tensioning bolt. Extend the ram slightly, making sue it is filled with oil. Attached a gauge of sufficient range and an air bleed valve to draw off excess air. As you increase tension the ram would apply pressure to the gauge.
You might be able to due the same with an electronic load cell. Some possibilities if you really want to know.Don
Don,
All true, but at some point you have to wonder how far you want to go with this thing. I am in the process of stepping back and looking at this analysis thing and saying: Hey, what are you trying to do. Oh yes, compare what you are doing with the "industry standard". And how important is this?? I am starting to say...Good question! It looks like the best I am getting is somewhere between 4,000 and 5,000 psi max from the standard delta spring according to my makeshift strain gauges. I think I should order a high performance spring from Iturra designs. If I want to have a way to test the stress on the blade, the easy way would be to get their stress gauge. Now it is starting to get expensive. According to the Iturra designs people, the next step after that might be to increase the hp of the saw from its 1 hp to 1 1/2 to 2 HP. I don't know how little I could get away with in replacing the standard motor with a 1 1/2 to 2 HP motor. Any guesses anyone?
I just bought a 1/2HP 110/220V 1725RPM Baldor for my new drum sander. It set me back CAD$138.00 (distributor cost).
My King Industrial 14" 1HP saw has some brand X 1 HP offshore motor. It has loads of go for what I need. I have resawn lyptus, Kentucky coffee tree, red oak, white oak, paduak, tigerwood with no real problems as long as the saw is kept properly tuned. I f I try to feed to fast the belts will slip - I changed the 2 drive belts to the Fenner style link belt. I would rather the belt slips than overheat the motor.Why are you wanting to increase the motor HP?Don
For my shop, I probably don't really have to change it, but I would not say it has "loads of go". I resawed brazillian cherry about a year ago, and if I had to do that many times, I would go for a 2 HP for sure. I would also increase the tension based on what I know now. I probably had about 2500 to 3000 psi on the blade when I did that.
However, for most other woods, including oak, I am probably just fine with my 1 HP for a home shop. If I up the HP, I would do it just to see what I could get out of a 14 inch saw and that would probably be the only reason, I don't think I can justify the cost for the amount I use it just based on use alone.
I am thinking that the motor upgrade is going to set you back over $200.00 at least. That is $200.00+ that you could put towards a 16 or 18 inch saw with the heavier everything. Like upgrading you existing computer, you could end up spending more than an equivalent replacement.
The Busy Bee/ Craftex people in Canada are selling their 18" 2HP unit for CAD$850.00.
Grizzly will sell you a 14" 2HP saw for US$850.00 plus freight. This saw has a 10" height, so saves the cost of the riser.
I nearly jumped at a 16 Laguna last fall, but went for a walk and asked myself have I truly outgrown the 14". I could not answer yes at this point in time.
If you have the room and find yourself changing blades for different tasks, you might make a case for having a dedicated resaw and a second for general sawing. Like we get to do with router purchases :-)Don
I made a jig from John White's design. It works well for me on my 20" bandsaw. I would recommend looking at Roland Johnsons video currently on the homepage here on FWW. Its a common sense approach that gets close to what you need to get your bandsaw just about right.
Take a look.
dan
I replaced the spring on my 1966 Powermatic 20" but have never done a real tension test. I got the spring (actually I bought 3 different ones) from McMaster-Carr. They are die springs and there were so many options I bought several and picked the best one. I spent about $25 total, each spring was about $8.
As said above, seems like a sharp blade cuts perfect regardless of the tension.
Jim
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