Help Choosing a Countersink
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    Question Help Choosing a Countersink

    Hey All,
    I have to countersink a bunch of 6"x6"x3/8" steel angle for 3/4" flat head machine screws. Head diameter is 1.4375"

    Planning to get a 1.5" countersink. The question is:

    How many flutes? Readily available options are 6 flute, 1 flute "fluted", and 1 flute with the hole. I'll be doing this on a Bridgeport, 1hp.

    Any thoughts would be appreciated.
    Thanks.

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    I'd be looking for a countersink with carbide inserts and more than "single flute." If this is hot-rolled material, the oxide layer will play h&ll with the cutting edge. With a single-flute cutting edge, the side load will be trying to move the mill's head all around and slip the knuckle clamping. This does not sound like much fun on a Bridgeport even with multiple flutes.

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    O flute style. I swear by them, not at them.

    Scroll down about 2/3.

    McMaster-Carr

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    The less flutes the better probably. You’ll really need to lean on a 6 flute to prevent chatter.

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    An M head Bridgie? I'd either go zero flute or piloted 3 or 4 flute.

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    The secret to getting a clean chamfer is to drill the countersink profile FIRST, then drill the holes after.

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    Over the years I've used a variety of different style countersinks, from 0 flute to 6 flute. The ones that seem to do the best are the MA Ford Uniflute style like this.

    MA Ford 61150002 1-1/2 HSS Uniflute Countersink 82-Degree | eBay

    When getting above 1" they aren't cheap, but they seem to outlast any others I've used except KEO. I purchased a sharpening fixture several years ago and have sharpened several different sizes rather than replace them. I'm not sure if MA Ford still sells the fixture. Several suppliers say "out of stock". Here's a link to an older MA Ford catalog with the sharpening fixture on page 382.

    M.A. Ford Catalog 2014

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    I would go with as many flutes as I could get and start off at the slowest RPM moving up until it starts to chatter then back off a little. Take as large a chip as it will comfortably take to increase tool life.

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    So I had to bite the bullet a couple hours after I posted the original question. All of this helped immensely for the future but I went with an M.A. Ford 6-flute. My reasoning was that 6 flutes would prevent the side-to-side and back-and-forth movement of the spindle, while reducing chip load on each tooth.
    It worked great at 135 RPM on the steel. Chatter in a couple spots of each hole, but for the most part was calm and cool.
    Thanks for all the input everyone.


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