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Rifles, Reloading, Optics, Equipment
Gunsmithing
Rechambering melonite barrel?
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<blockquote data-quote="Trickymissfit" data-source="post: 1293225" data-attributes="member: 25383"><p>carbide and ceramic tools don't really cut metal as we'd like to think. They push the metal off the surface. Where as a good high speed tool tends to slice the metal off the surface. Carbide's main advantage is it's ability to handle heat, and ceramic will take even more. </p><p></p><p>A lot of metal work hardening is due to not getting into fresh metal, All metal that has some carbon in it work hardens a little bit. Some more than others due to alloy make up. Steels that are heavy with chrome and nickel work harden faster and easier. All this leads into the term "surface cutting speed." There's a lot going on with that phrase, and the folks that figured it out are a hell of a lot smarter than I am. Plus a major portion is trial & error. You learn that softer metals want a higher surface speed. Metals that are known to be tough and will work harden will want a slow speed with a heavy feed rate. Yet all this changes with the Rockwell and method of cutting. High speed reverts back to the lower rate of speed, but carbide and ceramic was a much faster surface speed. I honestly can't comment on diamond inserts for a couple reasons. I've only used them on pretreat steels and aluminum, and even then it wasn't often. You get into something that has a .025" case at 64RC, and you got to get thru the first .010". The case decreases in hardness as you go deeper. If you only need to remove .008" or less, forget it. You can grind the .008", but that's about it unless it can be honed. Believe me a 64 RC is harder than most tools used. I highly recommend reading the Machinist Handbook for a good start, but there are some better sources. Seems like Valenite has a good manual (maybe Sandvik).</p><p></p><p>A good rule of the thumb is that a smaller diameter, the faster the rpm. Yet a slower feed rate. But cutting tools simply change everything. Carbide and ceramic want speed to force the chip string off the insert's surface. Two reasons come into play here. First is heat. If the chip stream leaves the cutting surface in a rapid fashion, and doesn't really stay on the insert; then all the heat goes out with the chip, making the part stay cooler and not imparting heat in the insert. It's also a good way to get burnt! Heat will actually harden some steels while cutting, and forget the idea that coolants will fix this. Still some metals don't want any coolant period (Ampco Bronze comes forth here). Ampco will harden so bad that that you can't touch it with a high speed tool, but still cuts better with high speed if done right.</p><p>gary</p></blockquote><p></p>
[QUOTE="Trickymissfit, post: 1293225, member: 25383"] carbide and ceramic tools don't really cut metal as we'd like to think. They push the metal off the surface. Where as a good high speed tool tends to slice the metal off the surface. Carbide's main advantage is it's ability to handle heat, and ceramic will take even more. A lot of metal work hardening is due to not getting into fresh metal, All metal that has some carbon in it work hardens a little bit. Some more than others due to alloy make up. Steels that are heavy with chrome and nickel work harden faster and easier. All this leads into the term "surface cutting speed." There's a lot going on with that phrase, and the folks that figured it out are a hell of a lot smarter than I am. Plus a major portion is trial & error. You learn that softer metals want a higher surface speed. Metals that are known to be tough and will work harden will want a slow speed with a heavy feed rate. Yet all this changes with the Rockwell and method of cutting. High speed reverts back to the lower rate of speed, but carbide and ceramic was a much faster surface speed. I honestly can't comment on diamond inserts for a couple reasons. I've only used them on pretreat steels and aluminum, and even then it wasn't often. You get into something that has a .025" case at 64RC, and you got to get thru the first .010". The case decreases in hardness as you go deeper. If you only need to remove .008" or less, forget it. You can grind the .008", but that's about it unless it can be honed. Believe me a 64 RC is harder than most tools used. I highly recommend reading the Machinist Handbook for a good start, but there are some better sources. Seems like Valenite has a good manual (maybe Sandvik). A good rule of the thumb is that a smaller diameter, the faster the rpm. Yet a slower feed rate. But cutting tools simply change everything. Carbide and ceramic want speed to force the chip string off the insert's surface. Two reasons come into play here. First is heat. If the chip stream leaves the cutting surface in a rapid fashion, and doesn't really stay on the insert; then all the heat goes out with the chip, making the part stay cooler and not imparting heat in the insert. It's also a good way to get burnt! Heat will actually harden some steels while cutting, and forget the idea that coolants will fix this. Still some metals don't want any coolant period (Ampco Bronze comes forth here). Ampco will harden so bad that that you can't touch it with a high speed tool, but still cuts better with high speed if done right. gary [/QUOTE]
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Rechambering melonite barrel?
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