Fall, 2009 | Front Page | | < Previous | | Next > | Volume 3, No. 4

As detailed in the Summer 2009 “Last Word” article, the new Starrett Versatix MP band saw blade has achieved outstanding results with interrupted cuts, structural work pieces and with pull-down saws. This article is an overview of the process used to develop this radically better product.

Why Blades Fail Band saw blades usually fail due to one of the following reasons: 1. The teeth gradually wear until they     no longer cut efficiently 2. The blade starts to cut “off-square” 3. The blade body fractures due to metal fatigue 4. The teeth fracture prematurely due to overloading Versatix was developed primarily to address #4 -- premature teeth fracture or “tooth stripping” due to overloading. Our objective was a balanced design to produce high tooth strength without significantly compromising cutting speed. For blades that usually perform well cutting solid sections, tooth stripping is most common when cutting metallic materials such as structural I-beam, H-beam steel members and tubular sections of varying section thickness. Tool Stripping Analysis Resistance of the cutting force (x) by the saw tooth results in tensile forces along the rake face. Tooth stripping occurs when the cutting force (x) acting on the cutting face (rake) exceeds the fracture strength of the material.

Blade Design – The First Round Initially, our focus was on an “extended tip” design. Following disappointing performances of several extended tip blades in our benchmark testing, we went back to the drawing board.

“Finite Element” Stress Analysis There has been very little scientific research related to the complex physics of multi-toothed cutting tools such as band saws blades. Consequently, published academic research is scarce, and most advances have occurred through the process of trial and error. Recently, however, “Finite Element Analysis” (FEA) has become available. Using powerful computers, millions of calculations can be performed to simulate the sawing process, permitting “Virtual Product Development” (VPD). FEA has provided us with a faster design cycle, months rather than years, and more comprehensive product knowledge from our tests. This process involves:  • An electronic drawing of the artifact is downloaded into the FEA software.  • The operator programs the FEA software to sub-divide the artifact using a meshing system.   • The mesh is more concentrated at the critical areas (in this case, the tooth tip).   • Each mesh intersection is a point where stress, temperature, strain, etc. are calculated. Each calculation has a relational knock-on effect with neighboring areas.    • The forces acting upon the model are specified, that is, where the tooth tip contacts the work material.    • Algorithms such as Young’s Modulus of elasticity, shear modulus and loading are applied to the model as part of the programming. The Versatix Design The result of our analysis, design and testing was a new blade geometry with the following characteristics: • A balance that produced high tooth strength without significantly compromising cutting speed • Curvilinear design to reduce stress “Hot-Spots” and promote smooth chip flow  • Shallow primary relief angle for tooth strength  • Small rake angle for tooth strength  • Increasing rake angle as flank wear proceeds to offset reduction in cutting speed due to wear  • Reduced Pitch/Tooth Depth ratio for tooth strength A New and Better Blade Cutting simulation with our proposed design indicated that we had produced the desired effect in strengthening the tooth. As field tests began, time after time Versatix’ performance and durability exceeded our optimistic expectations.

With our target interrupted cut applications, Versatix not only cut faster, but the incidence of blade fracture was dramatically lower than with other blades. In some applications, Versatix lasted as much as three or four times longer than the blades they replaced. In solid cutting applications, the Versatix 6-10 proved to be a very good general purpose blade for stock 2” and under. After 30 to 45 cuts, Versatix actually cut faster. We believe this is because the rake angle increases as the blade wears. There was no doubt that with Versatix, we had a winner.

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