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Re: Band saw blade tension

 

Ed -? I tested your method and it's perhaps a little high (depending on if the threads are greased or not)
My go-to method for many years was very similar:- Tighten it as hard as a normal person can (not a gorilla?or a wimp) without?any aids (like a rag). but I never knew whether that was correct or?not.
I have the gear now, so set up the blade with the load cell and standard tensioning rod&knob?per the picture and tested it.
  • With degreased?threads (as it comes from?the factory) with one hand and no rag or other aid, I could only get it to 230lb tension which?is ~21000 psi?stress.? This is just over the limit for a?carbon steel blade and only marginally tight enough for a bimetal blade
  • Degreased, one hand?+ rag could get it to 270 lb tension which is ~25000 psi the upper limit of what you should run a bimetal blade.
  • With grease?on the threads and knob/washer/casting and one hand/no rag I could get it to 250lb tension, ~23000 psi just over the midpoint of the bimetal blade?
  • With grease, one hand?+ rag could get to 300lb tension ~28000 psi, well over the limit for bimetal on the small wheels of a 4x6.
  • With grease?+ rag and two hands I could get it to 330lb >30000psi
From these tests, if?you're normal strength like me, greasing the threads and doing it up as tight as you can?with one hand only, the tension will be right on the money.?
My problem is that it takes time to get it that tight and it hurts my hand, so I prefer to use other?methods.
But if you only tension the?blade once in a blue moon, then it's a pretty good method.

James -? It actually?needs to be tighter than '...just not slipping ...' , unless you have the bow weight wound back to where there's?not much weight on the teeth in the cut (i.e. bow weight <5lb). If this works for you, the bow weight will be significantly less than you could apply (8lb max on a 4x6 ) with good tension, so the saw will cut slower than it safely could.
Low blade tension and bow weight >5lb sends the blade into a degree of 'elastic lateral torsional?buckling', where the top edge of the blade tips sideways. Then the blade?cuts off angle.The more bow weight, the more it tips. It's elastic so the blade just straightens up without damage?afterwards, often pinging away from the cut face at the end - jv

On Sat, Oct 30, 2021 at 9:45 AM n5kzw <n5kzw@...> wrote:
The method I use was posted on rec.crafts.metalworking.? First tou tighten the blade as much as you can with your hand, then you throw a shop rag on the tensioning knob and see how much tighter you can get it.? This method has served me well on my HF unit for many years. - Ed

Loadcell on nRF128.jpg

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