Cut rifling 4140 steel
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  1. #1
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    Default Cut rifling 4140 steel

    Hi all, I`m having problems with my cut rifling of 4140 blank barrels, ,45 cal. I use a T/C cutter at 5% forward angle in cutter box on a sliding ramp , coolcut cutting oil and pull through by hand. The problem is cutter rips small chunks and leaves scratch's in the groves, so that am I doing wrong, would love to get a nice smooth finish in the rifling, , help. Homebrew.357.
    p1010211-1-.jpgThe cutter head.

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    I'm guessing it's a combination of cutter geometry and lubricant. It may also be stability within the bore, if it's not a close fit it can bounce around, and as it does so it'll dig in and cut more than it should.

    For the lubricant, you may want something with more extreme pressure additives, maybe try Moly-Dee or similar.

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    I am no professional at this but here is my take. I assume that "I use a T/C cutter" means a tungsten carbide cutter. I am not sure that is the best choice as you probably need a real keen edge on the cutter since you are really just scraping the metal in this process. Fagersta WKE45 Swedish Tool Steel has a good reputation for use in cut rifling machines.

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    Will second HSS over carbide for work like this, carbide doesn't usually like to go slow, or to stay sharp like high speed steel. Also, do you have clearance on the sides for the spiral?

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    make sure of your positive rake and sufficient relief on top of cutter. Check straightness of barrel, close fit of cutter body is recommended but maybe hampered if barrel isn't straight. Not had a problem with carbide cutter myself. Only take small cuts 0.0001" - 0.00015". The peak of the angle of the ramp on the underside of the cutter should be forward of the front face of the blade.

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    My experience with annealed 4140 is that is its nature, material welds up to the tool edge then lets go. The only time I got good finishes was with negative rake tools and lots of speed and feed. Not sure if heat treated or annealed material is common for barrels. In any case negative rake would not work for rifling, suggested high speed steel looks like the best option.

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    Pulling through by hand ---is the obvious problem ....Get a power draw ,speed up the cut x10 ,and your problems are solved.

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    OK, thanks guys for all that, will see what I can sort out from it. I thought T/C would be the best as my gun drills are still sharp after drilling 28" of 4140 .444" hole with only 300/400 oil pressure. Will look at keeping to a very fine cut each pass when pulling through the bore and I do give the cutter a bit of a hone after six groves. But it`s no surprise I`m having problems with the backyard way I`m doing this. homebrew.357.

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    You need a scraping type of cutter or a negative rake. .0002 per pass


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