I tried a similar approach on a 16" band saw, except I clamped the two jaws of a 6" dial caliper to the blade. Seeing the small amount of measured deflection to give proper tension, I modified my setup. I measured the deflection over 12" to get more 'signal' and I also used a dial indicator that measures 0.004" over a complete turn of the dial (about 25 times the scale resolution of a typical dial gauge). These results showed my simpler setup was over estimating the tension by about 25% (cont..)
You are absolutely correct. I made the hole slightly larger that the dowel travels in and waxed the dowel with paste wax. It is much smoother now. Good catch.
The needle jumped because the blade doesn't stretch smoothly - its stretches in a 'jerky' fashion. A DI that measures to 0.0001" would jump as well. Let's not get carried away here. Ball park is all that is needed. I now have a method to get me very close to 15,000psi where I didn't have a clue before.
two questions for you: 1) Where did you get the 5800#/thou figure? Was that found in a book or google or??? 2) Does the type of blade (bi-metal for example) make any difference in the tension amount? I love the simplicity of this jig. Makes me wonder why I never thought of something like this before....
I agree, you are just trying to set a reference compared to the built in tension gauge (which is rarely accurate). I suspect the jumping is from the dowel binding inside the wood leg. Being that the blade being tensioned is just like a big stiff spring, jumping is unlikely.
Nice. I have less blade breakage at the proper tension on my 3 wheel bandsaw, better cutting results too. I was not using enough tension before. Do you have any tables for the proper blade speed when resawing different types of wood from Cedar to dense hardwoods? Or perhaps the feed rate is where to compensate.
(S/D) x 29,000,000 ---->Young's modulus for steel S = blade stretch in inches D = length of blade measured in inches (0.001”/5”) * 29,000,000 = 5,800 psi Answer 2: Use the same tension regardless of whether the blade is carbon steel, bimetal or carbide-tipped.
Brian, my bandsaw has an adjustment on the tension arm that can be "recalibrated". I wonder if you have ever tried to recalibrate it to your reading on the dial indicator and changed to another blade size and did it again. If so did the "recalibrated" built in indicator follow in a somewhat linear reading? Enjoyed the video and thanks. Bobby
You have a unique setup with 2 means of measuring the tension and I just wondered if setting the tension at .0025 always produced the same measured tension on your bandsaw's pointer. If there is a variance between the two, does it point to the inaccuracy of a traditional bandsaw tensioner quage? That's what we all have and you have means of testing it. I never miss your videos. This was another good one. Thanks
Not sure what you mean by "repeatable"? I can apply 1500 psi to the same blade over and over again. All that is required is to apply tension until I read approx 0.0025" on the DI. If by repeatable you mean reaching the same reading on the BS internal tension gauge with approx 0.0025" on the dial indicator, then yes it is repeatable.
Thank you for the video and the math. Do you need to do anything to the jaws clamping the jig to the blade to prevent slipage? And, somewhat related, have you ever heard about using a guitar tuner to measure blade tension? Frequency can be converted to tension. Seems like another interesing alternative. Cheap app to measure frequency when the tensioned blade is "plucked" is available for any smart phone. Thanks again for producing such an informative video.
Nothing is needed, in my experience, to prevent slipping. I have heard of the "plucking" technique before, but I have never tried it. My suspicion is that the frequency technique would come with a larger degree of error than the method described in this video and it might involve a tricky calibration of known tensions and frequencies.
WOW, that was vary informative. I'm going to pick up a dial indicator as soon as I can. My only question is what is the tension for 1/8, or 1/4. I run from a 1/8 to a 3/4, the biggest my saw will take and all those blades can't run at the same tension. I would think that a 1/8 would snap at the same tension as a 3/4. Thanks.
The suggested tension is the same regardless of the width of the blade. A 1/8" wide blade will require less force to reach the SAME tension as a 3/4" blade. The wider the blade the more force is required by your bandsaw spring to reach 15,000psi of tension.
I think you under estimate the accuracy of this method, although it will probably do a 'good enough' job. Using a dial gauge that has a basic scale resolution of 0.001" to measure 0.0025 of deflection is really pushing it. Did you see how the needle jumped as you increased blade tension? Any slop (side to side) in your fixture will also show up as changes in deflection. (continued...)
Its a very useful tool and I will make one. However, one query you are using the measurement of blade length as 5" but you cut the vertical member at 5" but you are clamping the blade on the cross members, are you not extending that measurement to 5" plus half the cross members? Should you measure between the two bolts? thanks James
The gauge in the bandsaw measures tension. As blades stretch and get slightly larger, the same tension will be required and registered on the bandsaw gauge. Therefore, blade stretch over time will be inconsequential.
nevermind i read the comments that said it didn't matter. but since a 15k psi moves the needle barely, can i magnify this by increasing the measurement distance from 5" to say 15"? I just have to divide the reading by 3, correct?
It doesn't go on tight enough to affect the set in the teeth. It's just tight enough to prevent it from slipping as the blade stretches. I don't think you could disturb the set even if you really cranked down on it.
This is an amazingly good video that is going to save me over $500.00!!! Thanks for sharing this!! A quick and important question though... Does .001" = 5800 psi over a 5" blade length for blades of all widths and thicknesses? Or do I need to use a different scale to get the same tension on other width and thickness blades? If so, where can I find a conversion table? :-)
Ok... don't worry... I think I just found the answer in your replies to others below. The amount of stretch over 5" stays the same for the same amount of tension regardless of blade size. I hope I have that correct. :-)
Great video. Are the other pieces of wood you used also 5" in length? What size dowel and hole did you drill in the piece of wood? Do you have any complete plans for your gauge. I am very new to woodworking and I need all the help I can get. Looks like you used some type of hardwood for the gauge. Is this correct?Thanks for your help and concern in this matter.
No problem. It is a little confusing. I just finished a page on my website that answers your question as it is pretty commonly asked. I hope it helps. www.garagewoodworks.com/BS_Tension.php
Using your setup will get you in the ball park, but you still need to fine tune the tension by checking blade side deflection, plucking tone, or using other time tested methods
Your actually talking about this backwards, use a gauge that gets repeatable, accurate measurements then test with a "gut feeling" test. Any way you can measure something with rulers, caliper or gauge that is a measurable method is better than any time tested method that has no actual measurable method.
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I tried a similar approach on a 16" band saw, except I clamped the two jaws of a 6" dial caliper to the blade. Seeing the small amount of measured deflection to give proper tension, I modified my setup. I measured the deflection over 12" to get more 'signal' and I also used a dial indicator that measures 0.004" over a complete turn of the dial (about 25 times the scale resolution of a typical dial gauge). These results showed my simpler setup was over estimating the tension by about 25% (cont..)
You are absolutely correct. I made the hole slightly larger that the dowel travels in and waxed the dowel with paste wax. It is much smoother now. Good catch.
Excellent video Brian. Thanks and I have one of those on my "To-Do" list for sure !
Really enjoy your videos man !
The needle jumped because the blade doesn't stretch smoothly - its stretches in a 'jerky' fashion. A DI that measures to 0.0001" would jump as well. Let's not get carried away here. Ball park is all that is needed. I now have a method to get me very close to 15,000psi where I didn't have a clue before.
two questions for you: 1) Where did you get the 5800#/thou figure? Was that found in a book or google or??? 2) Does the type of blade (bi-metal for example) make any difference in the tension amount?
I love the simplicity of this jig. Makes me wonder why I never thought of something like this before....
I agree, you are just trying to set a reference compared to the built in tension gauge (which is rarely accurate). I suspect the jumping is from the dowel binding inside the wood leg. Being that the blade being tensioned is just like a big stiff spring, jumping is unlikely.
Very infomative video will be making one, love your videos keep up the good work.
Nice. I have less blade breakage at the proper tension on my 3 wheel bandsaw, better cutting results too. I was not using enough tension before.
Do you have any tables for the proper blade speed when resawing different types of wood from Cedar to dense hardwoods? Or perhaps the feed rate is where to compensate.
(S/D) x 29,000,000 ---->Young's modulus for steel
S = blade stretch in inches
D = length of blade measured in inches
(0.001”/5”) * 29,000,000 = 5,800 psi
Answer 2: Use the same tension regardless of whether
the blade is carbon steel, bimetal or carbide-tipped.
Brian, my bandsaw has an adjustment on the tension arm that can be "recalibrated". I wonder if you have ever tried to recalibrate it to your reading on the dial indicator and changed to another blade size and did it again. If so did the "recalibrated" built in indicator follow in a somewhat linear reading?
Enjoyed the video and thanks.
Bobby
This is brilliant! I have a dial indicator and I have a bandsaw but I have no way of determining the tension…yet.
You have a unique setup with 2 means of measuring the tension and I just wondered if setting the tension at .0025 always produced the same measured tension on your bandsaw's pointer. If there is a variance between the two, does it point to the inaccuracy of a traditional bandsaw tensioner quage? That's what we all have and you have means of testing it. I never miss your videos. This was another good one. Thanks
Great device...
What would be a good indicstor for this?
Not sure what you mean by "repeatable"? I can apply 1500 psi to the same blade over and over again. All that is required is to apply tension until I read approx 0.0025" on the DI. If by repeatable you mean reaching the same reading on the BS internal tension gauge with approx 0.0025" on the dial indicator, then yes it is repeatable.
Thanks for the video. How did you thread the wooden nuts on the bolts? Did you use tnuts or threaded inserts?
Just curious. Have you tested for repeatability and will the same blade test differently after some use?
Thank you for the video and the math. Do you need to do anything to the jaws clamping the jig to the blade to prevent slipage? And, somewhat related, have you ever heard about using a guitar tuner to measure blade tension? Frequency can be converted to tension. Seems like another interesing alternative. Cheap app to measure frequency when the tensioned blade is "plucked" is available for any smart phone. Thanks again for producing such an informative video.
Nothing is needed, in my experience, to prevent slipping. I have heard of the "plucking" technique before, but I have never tried it. My suspicion is that the frequency technique would come with a larger degree of error than the method described in this video and it might involve a tricky calibration of known tensions and frequencies.
WOW, that was vary informative. I'm going to pick up a dial indicator as soon as I can. My only question is what is the tension for 1/8, or 1/4. I run from a 1/8 to a 3/4, the biggest my saw will take and all those blades can't run at the same tension. I would think that a 1/8 would snap at the same tension as a 3/4. Thanks.
The suggested tension is the same regardless of the width of the blade. A 1/8" wide blade will require less force to reach the SAME tension as a 3/4" blade. The wider the blade the more force is required by your bandsaw spring to reach 15,000psi of tension.
I think you under estimate the accuracy of this method, although it will probably do a 'good enough' job.
Using a dial gauge that has a basic scale resolution of 0.001" to measure 0.0025 of deflection is really pushing it. Did you see how the needle jumped as you increased blade tension? Any slop (side to side) in your fixture will also show up as changes in deflection.
(continued...)
Its a very useful tool and I will make one.
However, one query you are using the measurement of blade length as 5" but you cut the vertical member at 5" but you are clamping the blade on the cross members, are you not extending that measurement to 5" plus half the cross members? Should you measure between the two bolts?
thanks
James
No. The clamping force from the bolt is spread over the entire surface of the wood contacting the blade.
tks a lot
Good idea on writing in the gauge on your bandsaw for each blade width but bandsaw blades stretch over time so soon it won't be accurate
The gauge in the bandsaw measures tension. As blades stretch and get slightly larger, the same tension will be required and registered on the bandsaw gauge. Therefore, blade stretch over time will be inconsequential.
Wouldn't that stress the blade
How would you do this for a bench top band saw?
Joseph
Lorentzen
does the formula apply for different width blade and thickness?
nevermind i read the comments that said it didn't matter. but since a 15k psi moves the needle barely, can i magnify this by increasing the measurement distance from 5" to say 15"? I just have to divide the reading by 3, correct?
See here: www.garagewoodworks.com/BS_Tension.php
I see that this was done 8-9 years ago, but I'm wondering if you are concerned about affecting the set of the teeth where the gauge clamps on.
It doesn't go on tight enough to affect the set in the teeth. It's just tight enough to prevent it from slipping as the blade stretches. I don't think you could disturb the set even if you really cranked down on it.
@@GarageWoodworks Thanks for the reply.
Would this work with a 3" version as long as the calculations are re-done? I only have a small 10" Bandsaw
+Eddy W Yes. It will work.
Thanks for the prompt reply and the help :)
My calculation comes out at 9666.7 does that sound right?
+Eddy W It depends on what you use for D. See here: www.garagewoodworks.com/BS_Tension.php
S=0.001 and D=3 then times by 29,00,000
This is an amazingly good video that is going to save me over $500.00!!! Thanks for sharing this!! A quick and important question though... Does .001" = 5800 psi over a 5" blade length for blades of all widths and thicknesses? Or do I need to use a different scale to get the same tension on other width and thickness blades? If so, where can I find a conversion table? :-)
Ok... don't worry... I think I just found the answer in your replies to others below. The amount of stretch over 5" stays the same for the same amount of tension regardless of blade size. I hope I have that correct. :-)
+Napier Thompson Yes. Blade width has no influence on the calculation. See here: www.garagewoodworks.com/BS_Tension.php
+GarageWoodworks Thankyou so much for the reply. You have been a great help! :-)
Great video. Are the other pieces of wood you used also 5" in length? What size dowel and hole did you drill in the piece of wood? Do you have any complete plans for your gauge. I am very new to woodworking and I need all the help I can get. Looks like you used some type of hardwood for the gauge. Is this correct?Thanks for your help and concern in this matter.
Oh ok just wanted to make sure it doesn't shorten the life of the blade. Thanx
Calculus and physics and I couldn't come up with the answer until you told me. Duh on my part. Thanks for the answer.
No problem. It is a little confusing. I just finished a page on my website that answers your question as it is pretty commonly asked. I hope it helps.
www.garagewoodworks.com/BS_Tension.php
Using your setup will get you in the ball park, but you still need to fine tune the tension by checking blade side deflection, plucking tone, or using other time tested methods
Your actually talking about this backwards, use a gauge that gets repeatable, accurate measurements then test with a "gut feeling" test. Any way you can measure something with rulers, caliper or gauge that is a measurable method is better than any time tested method that has no actual measurable method.
Any time you put tension on a bandsaw blade you are stressing the metal. It's unavoidable and actually the intention.
Now you have finnished with your tension guage I will have it to save you cluttering up your shop HA HA
I priced a commercial blade tension gauge at over $250.00.
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