> Just some additional considerations on coated bits. Keep in mind that the
> shiny part at the tip of the bit does not do the cutting. The point of the
> tip becomes the guide for entry. The cutting portion is the swirled edge
> of the bit. This coupled with the degree of angle provides the ease of
> entry. Sharper angles provide faster entry but dull faster. There is
> always a trade off. There are min's and max's to angle setting where too
> little or too much will not cut. Since the bit is totally covered with its
> coating the very edge does have the coating and does aid in extended life.
> The most important statement in IMHO was carbon versus HSS (high speed
> steel) where HSS is far superior and coated HSS bits further extend the
> life but to what degree has much to do with speed, pressure, etc. as
> stated. As a side note on free hand sharpening where many go wrong is
> changing the angle and twisting/turning the bit when sharpening. The
> proper way is to align/match the existing angle with the grinding wheel
> (dressed/flat) and place the bit to the wheel and lift up slightly without
> turning or twisting the bit. Light pressure is all that is needed.
> Applying too much pressure will grind more than is needed and make the two
> sides that you need to sharpen unequal and useless. Grinding stone grade
> for each application is also important along with many other items. Edge
> life, and thus 4-5 sharpenings is good, is more a function of material
> being cut followed by speed and pressure. Drilling stainless and drilling
> a TR body panel will result in different edge life. Drilling body panels
> and having to sharpen after 4-5 holes indicates other problems that would
> need addressing. I have used the same bit to drill soft metal like body
> panels for a long time. The need for pressure has more to do with dull
> blades. Like a hand saw, no pressure should be applied except to the
> extent of keeping the cutting edge on the material being cut. The teeth,
> if sharp, will do the cutting and pressure should match the cut speed of
> the saw. If you go to fast or apply too much pressure the gullet area of
> each tooth will get clogged, burn/heat the material and not allow for the
> cut material to be ejected, thus not maintaining cooling. Same applies
> with bits and saw blades whether steel or carbide tipped. Too fast and the
> curl of the bit will not eject material, cause heat from "blow by" and
> burn both the bit and the material. Again the same with saw blades, steel
> or carbide. Cutting tools whether steel, carbide or ceramic are designed
> for different applications, materials being cut, speed and feed rates just
> to mention a few. The number of teeth, rim speed, kerf (thickness of cut),
> angles and application play heavily in design. So match the tool with the
> application. Just my humble opinion.
> Alex Manzo
> SunBelt Saw & Tool Co., Inc. (a lot of financial interest but no
> solicitation) :o)
> 72 TR6
> 59 TR3A
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