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Thread: Why release the tension?

  1. #61
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    Based on the responses, I'm not seeing any evidence in support of de-tensioning the blades. I would agree that if you're happy with doing it and that de-tensioning on your saw doesn't cause additional issues then it doesn't hurt to do it and errs on the side of caution.

    Scientifically, the question comes down to the response of the materials when put under tension in the saw. I assume most if not all spring mechanisms in these saws are made from coiled spring steel which likely are well within their elastic region and likely to have an equivalent infinite life at the stress values seen by the materials. My saw has shown this to be true with no effect on the springs. It comes to mind that we don't know if a manufacturer may have used cheaper materials or have spring designs that are going beyond their elastic properties.

    The remaining metal components involved include the wheels, bearings, fasteners and frame components. Once again these are expected to be loaded in their elastic region with an expectation of infinite life. Same argument would apply for a manufacturer using a poor design or incorrect materials - they could fail.

    I do think people hear about fatigue failures of springs and such (which can and does happen) but this is a different mechanism and requires repeated cycling. The stress in a bandsaw spring and other tensioned components is a constant while the machine is not in use. When in operation, the bearings, wheels, shafts, and such do have cyclic fatigue effects but this has no impact on de-tensioning while not in use.

    The remaining item would be the rubber tires on the wheels. This can vary and these type materials can creep enough to potentially cause an issue. I own a 20 year old Grizzly and while I'm not so confident the materials chosen for my tires were well engineered (maybe I'm not giving them enough credit - I can't say for certain). But even if it is by luck that my rubber tires are of a material that resists creep or taking a set under the loading presented by my saw, the fact is they have done so very effectively.

    One other item this relates to is the belts, motors, arbors and other related components on all of my machines are all under tension and also have metal and elastomeric materials. However, I don't nor do I see any designs which utilize de-tensioning each time I leave my shop. Granted they do require replacing under heavy use eventually and once again - maybe I've been lucky but I've never replaced a belt on my equipment either. I am a one man shop that took several years off of woodworking while raising our kids and such. My tools aren't used remotely like an industrial/commercial facility. However, my shop represents quite a nice case study of the long term effect of leaving these items under tension.

    My take on this after reviewing this as well as my personal use case is that a well made bandsaw should have no need to be de-tensioned.

    I also know that sometimes even a "well engineered" machine can sometimes have unintended flaws that couldn't have been foreseen initially. So the idea of doing it just in case is still valid. Certainly, if you have a saw that exhibited an issue from being tensioned then by all means do what you need to do for it.

    It really appears to be riskier to de-tension and possibly start it up this way or to tension it incorrectly. It also seems to like it could add additional wear on components that (at least in my saw's design case) aren't designed for repeated tensioning/de-tensioning.

  2. #62
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    Never! No problems.

    Did you ever buy that Lamello thingy? Bought my ex out of my house instead but is still on my radar when the $$ balance is back up.

  3. #63
    For years I worked for a family run mill work business....not my family. Some of them were detensioners and some were fogetabouters.
    All I can tell you is they never broke the machine.

  4. #64
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    Yep. For a time I thought I'd be good and detension when done with the saw. All it ever accomplished was to cause me trouble when I next needed the saw and forgot - despite all the clues I left myself - to retension. I quit after a couple of those episodes, and ten years on the same saw have never seen any ill effect from leaving tension on.

  5. #65
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    Quote Originally Posted by Larry Edgerton View Post
    Never! No problems.

    Did you ever buy that Lamello thingy? Bought my ex out of my house instead but is still on my radar when the $$ balance is back up.
    I didn't yet, I was hoping you'd buy it first and give it a good test so I'd know if it was a good idea! Sounds like you are probably spending wisely though. Was actually just thinking about it yesterday. It would make this current job easier to install, ought to just do it. I really don't like the domino, lamello might be the better mousetrap.

  6. #66
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    I have two bandsaws. The 20 year old craftsman has never had the tension released and seems to yuan fine on the original bearings and tires. The newer rikon is rigged with a micro switch that turns two led task lights on when itís under tension. That means when I leave the room and turn out the lights, the bandsaw nags me. In truth, I think the Craftsman runs smoother.

  7. #67
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    Some of the question of detension or not to detension comes down to the saw and the materials used in the critical parts.
    I just replaced the hinge for the upper wheel on my JET JWBS-14CS. This spent probably a decade where I just left it under tension. The upper hinge assembly is made from some cheap pot metal and distorted over time, to where the hinge was interfering with the shroud (I though I had a picture of that from before). This would interfere on adjustment and tensioning.
    old bandsaw hinge rotated.jpg
    This is the original hinge compared to an engineer's square. The hinge arm is bent, so that it interferes with the sheet metal shroud. The part where the arrow is pointing is where it would interfere.

    new bandsaw hinge installed rotated.jpg
    This is the replacement hinge with an iron pivot arm. (item 153303814248 from wmprice on ebay) I tried to email to make sure I got the correct assembly, but no response. Since the dimensions seemed correct I went ahead and ordered.
    The two arrows show where I had to use a file to trim the pot metal back a bit. If you do this have a file card around since the pot metal will clog up the file.

    When I first started to look into repairing this a couple of years ago, I tried emailing with Iturra but had issues with him responding. (I think I got a response to my first email, that my vintage saw could not have that problem, and then no response to my followup email. While by reputation the Iturra parts are probably better, I went with where I could deal with an online order (even though the email responsiveness was about the same))

    John

  8. #68
    Quote Originally Posted by John Stankus View Post
    ... the materials used in the critical parts. ...
    I de-tension a RIKON because it's easy, I don't have to even think about creep in the materials, and I swapped a mechanical for a tension-interlocked mag starter. Now even I can't mess it up.

  9. #69
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    Quote Originally Posted by John Stankus View Post
    Some of the question of detension or not to detension comes down to the saw and the materials used in the critical parts.
    I agree that this is the key issue.

    Specifically if zinc parts are used as in the example given by John. Zinc alloys are very susceptible to creep. For the technically inclined here is a link to some details:

    https://www.dynacast.com/en/knowledg...als/zinc-creep

    Note in particular some of the graphs are creep rate in % per 10,000 hours which is a little more than a year. So the takeaway for me is a less robustly designed part could be moving quite significantly over the expected lifetime of a machine.

    So in that case detensioning would be a good thing to do to prevent premature failure of the zinc part.

    Of course your mileage may vary.

    Tim Orr

  10. #70
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    I don't think you'll see a black and white difference. Most of the "I don't" people seem to not do it because they don't want to take the time to do it or because they will forget to tension it. I'd be in that group except for my Grizzly has a lever so it's quick and a key to turn on the power that gets hung on a magnet next to the lever when detensioned. In the long run I think it's better to remove the tension. It's just not easy to see any results. Most people would never notice if their BS has slightly more vibrations than when new. Most likely the bearings, while could be damaged, will still work just fine. In fact most would feel that if they got 25 years out of a bearing to be good. Yet that same bearing might have gone twice that, you'll never know.

    One thing is for certain. Very little, if anything, is under the same tension as a BS. Belts are the most common thing and the level of tension they see is a tiny fraction of what a BS is set up to.

  11. #71
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    Actually the tension on a bandsaw is very slight.

    I have a 90 year old motorcycle, I never detension the valve springs, they're doing just fine.

    Same for all the springs in dampers, Reeves drives etc.

    I guess if you have a "bandsaw shaped object" as opposed to a bandsaw it could be an issue, however with over 40 years in industry I have never seen a saw detensioned and many are 40 or 50 years old......Regards, Rod.

  12. #72
    I don't think the metallurgy or creep properties of the tensioning springs is in question (same for a motorcycle). It is the other parts of the system that give me pause.

    (A motor's valve spring is much more likely to break due to fatigue imposed by the high cyclic rate of load changes. I'd have to be really quick on the lever of a Rikon to replicate it.)

  13. #73
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    Quote Originally Posted by Malcolm McLeod View Post
    I don't think the metallurgy or creep properties of the tensioning springs is in question (same for a motorcycle). It is the other parts of the system that give me pause.
    (A motor's valve spring is much more likely to break due to fatigue imposed by the high cyclic rate of load changes. I'd have to be really quick on the lever of a Rikon to replicate it.)
    The tension spring was prone to "weaken" in the common older 14" Delta and Jet saws with cast iron frames. This happened to the one in my old Delta after about 10 years. I bought a replacement spring from Iturra and it was a better quality spring.

    Other tensioning parts of the system on the Delta did distort and had to be replaced, but the spring did too.

    I also fixed an old Jet with the same problem that John Stankus mentioned. The cheap metal had deformed. I was asked to stop by the community training organization and adjust the tension of the saw but didn't bring tools. Fortunately they found a file somewhere so I made it work.

    JKJ

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