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Starrett Bi-Metal Hole Saws are constructed of hardened, heat and abrasion resisting high speed steel teeth with a tough alloy body and cap. This gives them exceptional strength, durability and shatter resistance for user safety. Best for notching thick wall tubing.The "constant pitch" of Starrett hole saws have six teeth per inch, making for a smoother cut.
Here are some pointers to get the maximum life out of a hole saw:First of all, always select the best tooth configuration for the job you are doing. For notching purposes your general choices are:4/6 TPI variable 6 TPI constant Typically the 4/6 vary tooth is what most hardware stores and home centers sell. The vary tooth is the best choice for notching thick-wall (.175 and greater) round tubing and square tubing (held flat ways). The vary tooth is the fastest cutting of them all but encounters problems when cutting thin-wall material. What happens is the thin-wall will “drop” into the gullet of a hole saw. This is known as an “interrupted cut”. As one tooth breaks contact with the cut and the next tooth enters the cut, the shear force is so great that tooth breakage occurs - and frequently results in multiple tooth carnage. (This also holds true (especially) with band saw blades as well. Many of you have experienced the catastrophic failure of a lot of teeth when using a large toothed saw blade in too thin of material.)*The 6TPI constant tooth has the broadest range of effectiveness and will give most users the least amount of grief when notching standard size wall thicknesses i.e..083, .095, .120 etc. They are less “catchy” or “grabby” and less likely to wrench that drill out of your hand that you’re using. In the construction business it would be comparable to a wood circular combination blade - overall a good cutting blade but not the best for ripping and not best for fine crosscutting however it can do both effectively well.*Do not attempt to use carbide hole saws, annular cutters or end mills in a standard notcher. They will most assuredly self destruct (and they’re not cheap!). These type cutters need the rigidity of a mill or mag-drill.)*Get into the habit, before each cut, of checking all points of your notcher that may become loose. Make sure to secure the work piece so no shifting of any part will take place. Again this is probably the most common reason for early retirement of a hole saw.*As a general rule, the larger the diameter hole saw - the slower the speed.1” ............. 350RPM1-1/2 ........ 230RPM1-3/4 ........ 195RPM2” ............. 170RPMOne exception would be when notching thin-wall material. A faster speed would prove to be less of a chance of the hole saw catching on the tube.*Use a proper cutting oil. Motor oil is not a cutting fluid!*Do not “dive” into a cut. Ease into the material and allow the saw to pace its self. You should be able to “feel” how much pressure to apply.*Hole saws can quite often be “out-of-round” as a matter of speaking because of a wayward tooth on the weld joint. Filing it down from the side (not the top!) will not damage the saw but give you a truer cut.*Also get into the habit of checking after each notch to clear any remnant pieces of tube that may lodge and remain inside the hole saw. There's nothing more unexpected than to have one of those pieces engage and bring your project to an abrupt halt!