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Bandsaw blade tension problems

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Put a new blade on my 14" Delta clone and had problems getting the tension right.  I would get it setup and start cutting and the blade tension would loosen.  After going through everything I found the problem.  The blade tension spring had failed and would not keep the blade tight.  I was kind of surprised because I always loosen the tension when I am done and the spring is a pretty hefty one.  The springs cost about $10 and are easy to replace.  Lesson learned is to check your bandsaw over regularly with particular attention paid to things like springs that can fail.

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I suspect there was a manufacturing defect in the spring.  Is it still on warrantee?  


Keeping a spring loaded should not cause it to fail.  If that were a problem for spings, your car suspension would soon collapse.  The same applies to a bandsaw blade, which is basically spring steel bent over the wheels. The failure of springs and sawblades is repeated loading above a certain stress level that causes a fatigue crack.  In the case of bandsaws, the highest stress comes from bending over the wheel every time the blade goes around a wheel.  Actually, saw steel is very high strength, so you need an extremely high load to pull it apart in tension.   Assuming the steel was properly heat treated, and weld is properly annealed, the main reason for early failure is a defect/impurity in the steel or a scratch/knick on the surface which acts as a stress concentration.  

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Consider buying one of the "Cobra" brand replacement springs available from any of the on-line quality woodworking suppliers. These are heavy duty and I believe are available to fit Delta saws. I have a 40 or so year old 14in Sprunger bandsaw and actually ran it for several years without a spring after the original one broke. Last year I bought one of the Cobra springs and it works fine.


IItnsounds like the spring in your saw was improperly heat treated.



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As you discovered, the spring is an important part of the saw, particularly with regard to shock absorption while cutting.  It's likely that you could order a spring from Porter-Cable-Delta-etc that would be suitable at a reasonable cost.  I wouldn't buy a spring from a hardware store for permanent replacement.


Many people don't know or bother about relieving the tension on the bandsaw when it's not in use, to prevent wear and tear on the spring, blade, and flattening tires, and other parts of the saw.  There is a convenient device, a lever arrangement, that can be adjusted to quickly set the tension and relieve it after every use of the saw.  I don't have one, but I think it's a good idea.  Usually, I just back off the tension at the end of the work session, but sometimes I do forget.


There is a supplier of high quality parts and accessories for 14" saws:  Louis Iturra.  So far as I know, there is no website, but if you want good parts and advice, do a search.

Edited by Bob Blarney
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