Sorry Dave, blades that don't crack first don't exist.? Unfortunately?its actually built into the design of? 4x6.
Engineering-wise, repeated stress cycles induce cracks in any tensioned member, if the stress is high enough or its cycled long enough.?
Bandsaw blades get put under repeated stress cycles when they:
- bend around the bandwheels and straighten out again,
- bend across their width when tracking onto the top wheel and
- are twisted through the guides,
This happens whether the blade is cutting or not!
The critical thing is how much the blade bends in relation to its thickness, the thicker the blade the worse it gets for a given bandwheel diameter.
There used to be (pretty sure it doesn't exsit now) an industry association called the 'Hack and Bandsaw Manufacturers Association of America' who published minimum recommended bandwheel diameters for each thickness of blade. For our 0.025" thick blade, the minimum diameter bandwheel is supposed to be just under 12"!? Most 4x6's run 7 3/8" to 7 1/2".? That means the 4x6 bandwheels are less than 2/3 of the size they should be for blades to last.?
As a consequence they all crack. Doesn't matter whether they are bimetal or carbon steel (though maybe carbon steel might last a wee bit longer as the steel is not as hard - I haven't tested that)??
And they crack in a surprisingly short time. I set up tests with 6 identical brand new bimetal blades, tracking properly on one of my saws that had its guides removed, so the only cyclic stresses were the bending around the bandwheels and tracking on the top wheel and varied the tension from 15000psi to 27500psi (lowest recommended tension for carbon steel to mid-point tension for bimetal blades) in 2500psi steps and ran continuously until they failed.
I was expecting more than a week, but the longest lasted 56hrs and the shortest 21hrs! I dye-penetrant crack tested them; each blade had 20-40 cracks, all starting from the gullet of the teeth.?
These were cheap Chinese manufactured BiChamp brand, So I thought maybe its because my saw is so old (1987) and the blades are Chinese, so I bought a US-made Starrett blade and ran it, at the tension that gave 56hrs result before, on a new saw (yr2000 RF128). It lasted only 8hr (eight hours) of continuous running and did not break at the weld. This could have been a defective blade (but I'd paid top dollar for it!).
I have not been able to find any set of conditions or adjustments or any modification that significantIy extends blade life.? ?
This sucks, but its a fact - jv? ??
John Vreede