Manfre -
Looking at the referenced picture, it looks like what broke is a gusset on the bracket for the tracking adjustment rod? If that is the case, there really shouldn't be significant stress placed on that area during tensioning ...
The piece that broke is part of the tracking adjustment mechanism. While you are correct that there would not be much stress placed on the part in an absolutely ideal world -- the wheels are perfectly coplanar, the blade is riding perfectly centered, the blade is the correct length, and (most importantly of all) the blade was able to run
without any tension aplied to it -- the world is not exactly perfect or ideal. The more tension the user places on the blade the more the upper wheel will want to pivot downward and inward directly into the tracking knob -- that's why you need tension to effectively adjust tracking -- placing ever greater stress on the very part that snapped. That the part was diecast with as much reinforcement as it had is a good indication that a good deal of force will be applied to the part in normal service.
Sadly, manufacturers seldom 'over-engineer' diecastings -- they are pretty much optimized to produce a part for the bare minimum of cost and fuss despite their inherently brittle nature. I hate seing die-cast parts used in high-stress applications nearly as much as I hate seeing plastic used for the same (and I really hate the use of plastic 'springs' in otherwise perfectly good tools)!
If the user installs a large blade, say 3/4" on a 14" bandsaw, -- especially one a bit shorter than it ought to be -- and then dials up the tension until the factory tension gauge says its tensioned (at which point the over-short blade is now greatly overtensioned), then a considerable amount of force would have been applied to the tracking 'paddle' that counters the wheel's natural tendency to collapse inward and downward about its pivot/hinge. Many factory tension gauges assume that the installed blade will be at, or very near, the recommended length. Unfortunately, reality assures that some blades will be significantly shorter or longer than the recommended length which will result in the factory tension guage reading (inversely) either over-tensioned or under-tensioned even for a perfectly tensioned blade. That is why the factory tension gauge should only ever be considered a 'suggestion'.
I don't know that the above scenerio caused the OP's disaster, but it is a very likely scenerio by which a bandsaw owner can damage the bandsaw in the very same way. Ideally, the manufacturer should have over-engineered the assembly to survive overtensioning upto and beyond the point at which the tensioning spring is fully compressed. Unfortunately, they know that if it was a cheap bandsaw (relatively speaking) many non-mechanically minded buyers will simply blame themselves and purchase a new tool rather than trying to repair the damaged part (which is well beyond their mechanical abilities) -- so it becomes an opportunity to sell them another saw more often than it is a repair.
Rant: It just really irks me how common poor engineering and manufacturing has become. It's like my new air compressor (Kobalt, really ABAC iirc) -- a reasonably decent 3-cylinder single-stage design -- but the idiot assembly person (chinese made pump) assembled the bearing carrier plate with a gasket torn at 3 points (oil everywhere!) but continued to bolt it together despite having thoroughly mutilated the gasket! It takes *hours* to break the unit down to where you can remove the carrier plate and draft out and cut a new (and rather complex) replacement gasket just to fix a mistake that should never have been made in the first place and could have been corrected in mere seconds at the time of assembly. I could not help but wonder, after seeing how many tools I had laying about, whether the average air compressor purchaser would even own the full complement of tools -- much less possess the knowledge and experience -- to make that same repair. And it really is more of a repair than a return item at over 500lbs and nearly 7ft tall! That and the fact that unless an item is beyond reasonable repair I would rather repair the known defects in an otherwise properly functioning device than gamble on the unknown with an exchange!
...Ok, now back to the topic...
Just a few more cents -- or possibly yuans -- worth of opinion... :nah:
Thanks for listening!
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