The Unimat scroll saw uses a spring arm to maintain tension on the blade.
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With spring tension return jig saws when you run the saw too fast the spring does not have time to return and can not keep the blade under continuous tension, this causes the blade to flex and the blade will fail from repeated bending. (Think of bending a solid wire over and over, it gets hot at the bend and then it breaks at the bend from metal fatigue.)
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Thin fret and scroll saw blades can make tighter turns but you must keep the speed very low to maintain spring tension and avoid blade flex since the thin blade flexes more and it doesn't take long to fatigue the thin metal.
Thicker jig saw blades can last longer at slightly higher speeds since they don't flex quite as much but they can't make tight turns.
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Modern types of scroll saws use a parallelogram drive mechanism to maintain constant blade tension and also keep the blade perpendicular to the table through each stroke (assuming the table is not set at an angle) so the saw can be run much faster without premature blade failure.
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Of course there are other factors that contribute to premature blade failure such using a blade which has too many or too few teeth for the material, cutting stock that is too thick, or pushing the material into the blade too fast, all this can overheat and/or flex the blade causing it to fail no matter what saw you are using.
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Push the stock into the blade only as fast as it cuts, don't get in a hurry and force it.
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Also the teeth must cut toward the table....
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Richard
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