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Thread: Wooden Band Saw Blade Tension

  1. #16
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    Quote Originally Posted by Jim Dwight View Post
    It was mostly 3/4 plywood but the frame was a box frame of 3/4 plywood but it still would not tension a 1/2 inch blade. I added a 2x6 and it was better but still did not work great.
    FWIW, he made mention of this in his latest video. His comment was that plywood was a bad idea, because you wanted the grain all running vertically for strength. Looking at his current version it appears to have at least 4 2x6s in the frame, all running vertically.

    WoodenBandsawFrame.jpg

    I like Matthias's videos (both of them, there is one in Germany too and he also has a wooden frame bandsaw). He seems to be technically trained or at least inclined and I am confident his bandsaws work. But I do not believe they will do the work of a steel frame bandsaw. I wouldn't try a blade bigger than 1/2 inch and they may not tension that.
    I saw the video where he makes boards out of a tree by fastening the trunk to saw horses and rolling the saw to make the cuts.
    I was just looking at this video, and it appears he's using at least a 1" if not larger blade to do this milling, and it's over the entire span of the saw. His assertion is that it takes less force to tension a larger blade, which I believe is correct. However the manufacturer's assert that you need to put more tension on them because of how they are used. My 1/4" blade is used with maybe 4-5" between the guides, a resaw blade would be over a 12" span. Hence the requirement for more tension.

    You could be correct about the steel bandsaws, I'm sure there are a lot of reasons why manufacturers have moved to that design over the old cast iron.

  2. #17
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    Quote Originally Posted by Andrew More View Post
    FWIW, he made mention of this in his latest video. His comment was that plywood was a bad idea, because you wanted the grain all running vertically for strength. Looking at his current version it appears to have at least 4 2x6s in the frame, all running vertically.

    WoodenBandsawFrame.jpg



    I was just looking at this video, and it appears he's using at least a 1" if not larger blade to do this milling, and it's over the entire span of the saw. His assertion is that it takes less force to tension a larger blade, which I believe is correct. However the manufacturer's assert that you need to put more tension on them because of how they are used. My 1/4" blade is used with maybe 4-5" between the guides, a resaw blade would be over a 12" span. Hence the requirement for more tension.

    You could be correct about the steel bandsaws, I'm sure there are a lot of reasons why manufacturers have moved to that design over the old cast iron.
    Tension is tension. Large blades need just as much tension as smaller blades. Matthias's argument about larger (wider) blades not needing as much tension is correct in that they have higher beam strength ("I" again) but that only goes so far. Span between the guides doesn't change the requirement for tension, only for deflection with respect to beam strength. But in the end, a blade cuts straight, or not, based on how much tension is put on.

    My recommendation is to put a riser block on your 14" Delta if you want to do modest resawing and veneer slicing, and install a 1.5 to 2 hp motor. A 3600 rpm motor is fine, too. You may have to change one or both pulleys but it's OK to run it higher speed. Mine runs at over 3000 fpm. Faster is better for clearly sawdust from the cut. With this set up on my 14" Delta I cut hundreds of square feet of 10" and wider veneer with it. Deviations were usually less than 0.008" over a slice. It's half that or less on my new BS, but that's still good enough. I would cut veneer at 0.100" thick and drum sand it to 0.065" and rarely lose a piece. It takes patience, careful setup, and a sharp 1/2" x 3 tpi blade but it will do it. There's no need to go off on an adventure building a wooden bandsaw that will perform no better. My two cents.

    John

  3. #18
    I was a bit bored so when I went out to the garage to put on another coat of poly I measured the outside of the frame of my Jet. It is two tubes of steel totaling 5.5 inches by 3.25 inches. The dimension going away from you if you are facing the blade is not the important dimension, it is the dimension going to your left if you are facing the blade. The blade tried to reduce the depth of cut of the blade - pinch the frame in. In my saw's case, that dimension is 3.25 (about, I did not use calipers).

    It doesn't make a whole lot of difference if I assume 1/4 thick tubes versus 1/8 inch thick tubes. I got 10.5 inches to the fourth with 1/4 wall and 10.1 with 1/8 inch walls.

    So then I solved for what would be a big enough beam to offset the 15 times lower modulus of elasticity. Because of the direction of the force, you want more going to the left. If I assume 3.25 thickness (b in the equation) and a little over 12 going to the left, I can get enough thickness. The equation is I=bh3/12 so it makes a lot more difference what you use for the h than the b. But any wooden beam with an I a little over 1500 inches to the fourth should work. I don't think Matthias has that kind of mass in his frame.

  4. #19
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    In advance, I didn't read all the posts . . .

    A 1/2" bandsaw blade on a 14" bandsaw is adequate to resaw as long as the setup is properly completed. Check Alex Snodgrass (from Carter Products) videos for proper setup. You may not be able to just shove the board through as fast as you'd like, but it will do the job. The key is proper setup and a sharp blade. Stockroom Supply insists that even a 3/8" blade will work as long as certain guidelines are followed. I've resawed a number of boards at least 6" in width (some more) with excellent results, but the setup of the guides must be done correctly. As others appear to already have said, a 1" blade on a 14" bandsaw just won't work. My Rikon saw could use up to a 3/4" blade, but I'd never use more than a 1/2" blade. The 1/2" is sufficient to resaw.

  5. #20
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    FWIW, if one's motivation is a BS for resawing and veneer slicing, only, then you could build a rectangular frame and run any tension you wanted to, even on wide blades, with no worries about deflection. Wood is great in compression so the vertical sections wouldn't need to be very stout and an LVL beam or a couple of 2 x 8's would be more than stout enough across the short top and bottom span needed to build the frame.

    John

  6. #21
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    Quote Originally Posted by Jim Dwight View Post
    So then I solved for what would be a big enough beam to offset the 15 times lower modulus of elasticity. Because of the direction of the force, you want more going to the left. If I assume 3.25 thickness (b in the equation) and a little over 12 going to the left, I can get enough thickness. The equation is I=bh3/12 so it makes a lot more difference what you use for the h than the b. But any wooden beam with an I a little over 1500 inches to the fourth should work. I don't think Matthias has that kind of mass in his frame.
    I'm struggling a bit with this, so I might be off, but I believe you're using the wrong formula for a tube. I believe the one you used is for a solid beam, which would be the case for the wooden bandsaw frame, not the Jet. I believe the jet would the moment of the area of the tube, which I believe is (bd^3-hk^3)/12.

    https://www.engineersedge.com/calcul...re_case_10.htm

    So (bd^3-hk^3)/12 = 15*(bd^3)/12

    For your Jet, the area moment of Inertia works out to be:
    1/8" steel: (5.5 * 3.25 ^ 3 - 5.25 * 3^3)/12 = 3.92 inches ^4.
    1/4" steel: (5.5 * 3.25 ^ 3 - 5 * 2.75^3)/12 = 7 inches ^4.
    So the wooden version would need to be 58.8 inches ^4 to be the match the 1/8" steel version, and 106.0 inches ^4 for 1/4" steel.

    It's unclear to me how you got 1500 inches^4, seems like it should be 150 even with the simpler formula? 10.5 * 15 = 157.5 inches ^ 4

    Right now, guessing from the pictures shown, I'm guessing Matthias's version is 6" x 7.5" because I think he's using unmodified dimensional lumber, and you can clearly see 4 layers in the pic.
    (6 * 7.5 ^3)/12 = 210 inches^4.

    So right now, it appears that his wooden bandsaw would be 2-4x stiffer than your steel Jet, using the formula for a square tube, or slightly stiffer if we use the simpler approach. Am I missing something? I'm basically learning this right now, so my assumptions could be way off.

  7. #22
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    Quote Originally Posted by Andrew More View Post
    I'm struggling a bit with this, so I might be off, but I believe you're using the wrong formula for a tube. I believe the one you used is for a solid beam, which would be the case for the wooden bandsaw frame, not the Jet. I believe the jet would the moment of the area of the tube, which I believe is (bd^3-hk^3)/12.

    https://www.engineersedge.com/calcul...re_case_10.htm

    So (bd^3-hk^3)/12 = 15*(bd^3)/12

    For your Jet, the area moment of Inertia works out to be:
    1/8" steel: (5.5 * 3.25 ^ 3 - 5.25 * 3^3)/12 = 3.92 inches ^4.
    1/4" steel: (5.5 * 3.25 ^ 3 - 5 * 2.75^3)/12 = 7 inches ^4.
    So the wooden version would need to be 58.8 inches ^4 to be the match the 1/8" steel version, and 106.0 inches ^4 for 1/4" steel.

    It's unclear to me how you got 1500 inches^4, seems like it should be 150 even with the simpler formula? 10.5 * 15 = 157.5 inches ^ 4

    Right now, guessing from the pictures shown, I'm guessing Matthias's version is 6" x 7.5" because I think he's using unmodified dimensional lumber, and you can clearly see 4 layers in the pic.
    (6 * 7.5 ^3)/12 = 210 inches^4.

    So right now, it appears that his wooden bandsaw would be 2-4x stiffer than your steel Jet, using the formula for a square tube, or slightly stiffer if we use the simpler approach. Am I missing something? I'm basically learning this right now, so my assumptions could be way off.

    Your math is correct, however, you overlooked the point where Jim said the frame of his saw has TWO tubes, so you need to redo the calculation. With two tubes welded together you have to use a different approach to calculate the moment of inertia, like you would for a beam. Take a look at this reference: https://skyciv.com/docs/tutorials/se...-beam-section/
    Using that approach I came up with an I = 32 for Jim's bandsaw frame, assuming I did the calcs. correctly, using the data calculated from your link: https://www.engineersedge.com/calcul...re_case_10.htm

    So Jim's saw is still 15 / (210/36) = 2.6X stiffer if it's made out of 1/4" steel tubes. If the tubes are 1/8" thick then I = 17 and Jim's saw is 15 / (210/17) = 1.21 stiffer.

    For reference the tubes on my Grizzly bandsaw are made of two tubes that are about 6" wide. It easily tensions a 1" blade to 25K psi with throwing the guides out of alignment.

    There's a reason you don't see many people making bandsaws out of wood.

    John

  8. #23
    Well you are right that I had a math mistake, actually it looks like two. When I calculated the I for the column of my saw, I subtracted the I for the inside from the I for the whole thing, calculated as a solid beam (i.e. I=bh3/12). I think that is right, I found a reference to it. But when I calculated the inside, I only used one of them, not two. So my I for this beam was too high. I think it should be 7.94 in4 for 1/4 tubing and 4.48 in4 assuming 1/8 inch wall tubes. So when I then solve for an equivalently stiff wooden beam, I multiply these values by 15 (to account for the lower modulus of elasticity) I got 119 and 67.2 for the necessary I for the wooden beam. I'm just using my phone calculator so this isn't exact (i.e. it either doesn't have cube roots or at least I don't know where they are) but I think the beam fo the saw needs to be about 3.25 by 6.25-7.5 inches depending on what you assume my saw's beam is. But that dimension has to be in the direction away from the blade, not in line with the blade. I did not go back and look at Matthias's saw but I think it might have a big beam similar to this but it is not oriented this way so it will not be this stiff. But I didn't look so I am not sure.

    Sorry I messed up the math the first time. 2 2x8s would seem to get you in the ball park if you orient them correctly. That is true if the modulus used in the factor of 15 is consistent with softwood. It might have to be hardwood or bigger for softwood.

  9. #24
    I looked at his current big bandsaw build and I think he is a bit light. It looks to me like he laminated 7 boards about 3/4 thick for a "b" of 5.25 inches. There is a drawing briefly on the video that includes the H dimension but I couldn't see it clearly, it was something over 12. Matthias is in Canada and works in meters so I think this is cm so it would be 5.12 inches if I round up to 13 cm. That would give him an I of less than 60. So my guess is he will be able to use a 1/2 blade just fine but not be able to fully tension a 1 inch. Maybe a 5/8 or 3/4.

    I'm not really sure mine will tension a 1 inch. It is supposed to but I haven't tried by wider blade yet. I may have ordered a 3/4, figuring it might not fully meet the 1 inch spec. It wouldn't be that surprising.

  10. #25
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    I get the idea of making or repairing something yourself vs paying for it. I have a replacement heating element for my stove top coming any day. Would you save money? In the long run, probably not. What ever you make isn't going to have much valve if you sell it (the motor will). A brand name saw will. For example if you pay $1500 for a Grizzly saw chances are as long as you keep it in good shape it'll be worth half what you paid. If you decide to keep it then you could be dealing with wood movement and always be tuning the saw. You may even experience a failure which will require you to rebuild it. I wouldn't go too far into 26" must be better. If nothing you will do will need more than what you have now (your 14" saw) the extra really isn't of much value. If you are planning to get into woodworking and you will need it then I would say comparing it to a 24" bandsaw price wise would be comparable. The biggest advantage to a wider wheel besides throat depth is less flex of the blades allowing you to run a wider thicker blade.

    I'm not trying to talk you out of it, I actually would like to see you try and report back how well it works over the long term. Do you know someone who welds? I think I would be much more optimistic about a hybrid design. Mostly wood but with a steel skeleton.

  11. #26
    Randy, I pretty much agree but I would also say that there is a variety of 14 inch bandsaws. My biggest blade is a 3/4 which I have not tried yet but my steel frame Jet is rated to handle a 3/4 blade (I thought it was 1 inch but I went and looked). It is the jwbs14-sfx and weighs nearly 300 lbs. Thickness capacity is 13 inches. I have not tried nearly that yet but have resawn really hard wood, I think it was cocobolo, about 6 inches wide with a 1/2 inch blade. It breezed through that. I will try my 3/4 blade some day but I agree, a 1/2 will certainly work. Based upon my calculations, I think Matthias's wooden frame saws are lighter made but still might tension a 1/2 inch blade.

    I would guess that a saw like the HF 14 inch might not be as stiff as Matthias's wooden saws. I am pretty sure it is not as stiff as my Jet. But with a 3/8 or possibly 1/2 inch wide blade it should be capable of resawing wood within it's capacity. But only with a lot of fiddling around to get it running right. I would expect a wooden frame saw to require if anything more fiddling around. I never got the vibration fully out of my wooden frame saw and it had aluminum wheels.

    My advice to the OP is to do what I did and apparently you did and just buy a nicer steel frame saw (I was going to buy the "326" Rikon until I saw the Jet on sale and read it's reviews). But some people like to use tools they make, Matthias, both of them, certainly seem to be in that camp.

  12. #27
    Quote Originally Posted by Lee Schierer View Post
    Your 14" saw was never designed for nor is it capable of properly tensioning a 1" blade. Any blade over 1/2" is pushing the limits, even with beefed up tensioning springs. Before investing time and money on a new saw that you try the following:

    1. Buy a good 1/2" blade with 3 TPI.
    2. Align your saw table and fence to the blade. This video is the best I know of on how to align your saw.
    3. Insure your belt is properly tensioned so you get full power from your motor.

    Once you do these things, I think you will have a much improved bandsaw.
    Good stuff Lee. Thank you!
    "All that is necessary for the triumph of evil is that good men do nothing."

    “If you want to know what a man's like, take a good look at how he treats his inferiors, not his equals.”

  13. #28
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    Thanks Jim and John, this has been an interesting and enlightening discussion about mechanical engineering, even if we're all futzing the numbers a little bit. It happens.

    Alex - the resale argument is a very good one, and something I saw one of the people reviewing the 17" Grizzly bring up. He was arguing for even higher numbers than half price, but who knows how things will be, if I get it, and then sell it a few years later. I just had an interesting discussion with a guy trying to sell a Delta 13" planer for $800 when I can get the Grizzly version, only with 15", a warranty, and parts support for $1100.... I turned him down.

  14. #29
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    FWIW I got a reply back from Grizzly about their 17" band saw. According to them, their saw is made of 16 guage metal, which makes it 1/16th, far less than the 1/4" or 1/8" we had been assuming. Not going to run through the math again, but I think that make's Matthias's bandsaw stiffer than a Grizzly's.

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