Drill rumbles on entry
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  1. #1
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    Question Drill rumbles on entry

    I was drilling a 17/32" (13.5mm) hole in annealed A2, with an OSG coolant thru drill. It's in an ER25 holder with a bearing nut and a sealed, on size collet. Okuma M560v. Hole depth is 1.100" thru hole. I'm not spot drilling it. Just straight feed. When the drill enters, it rumbles until it's fully engaged, then sounds great. I looked at the tool closely and I don't see any chips or wear that would indicate an issue. I also dialed in the runout to within .0002" Should I look at a better holder or look at something else.
    Speeds & feeds:
    160 SFM
    .008" IPR
    1,000 psi

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    I'd try using a spot drill. Same angle or slightly larger than the drill.

    Or experiment with a two-stage drill code, where the first 1/8" or so is slower RPM and/or feed to establish the hole, then kick to the "regular" numbers for the rest of the hole.

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    Sounds like you aren’t using a centre, or you centre drill is the wrong angle.

    Is the drill a 118 deg standard?

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    What OSG drill? They make a lot of different ones, and they all perform differently. That said, I have never had any issues with their drills and I never spot!

    Also, how long is your drill? 3xD or 8xD ()?

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    You need a "soft start" to your drilling process. .008" per rev is aggressive, so start the first 1/4" at about .002" per rev, then up it once in the material. I created a subprogram to do this and it works great in 4340 and A2.

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    sounds like too much of a cut and not enough sfm.
    is there a pre existing hole there? I had that issue in a job where the hole was 5/8" and needed to be 1 9/32, drill was walking around too much because the large center hole. slow feed/rpm until it hit full diameter

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    No pre-existing hole. It's the HP255-5311. It's a 5xD drill. They recommend 160-240 sfm and .008"-.012" ipr on their chart for this drill in tool steel. I guess i'll try spotting with a 142°. I was told not to spot drill with coolant through drills but hey, I'll give it a shot. I'll also try slowing down until it's in the full diameter before going to the full speed and feed. Thanks guys

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    Quote Originally Posted by sirgreggins View Post
    No pre-existing hole. It's the HP255-5311. It's a 5xD drill. They recommend 160-240 sfm and .008"-.012" ipr on their chart for this drill in tool steel. I guess i'll try spotting with a 142°. I was told not to spot drill with coolant through drills but hey, I'll give it a shot. I'll also try slowing down until it's in the full diameter before going to the full speed and feed. Thanks guys
    I wouldn't use a spotter, just take the drill you have and feed it easy until its supported, then pile drive it.
    The drill is able to start itself now at .008 a rev, it'll start itself even better at .002 a rev or so.

    Might only need to get a small spot before picking up the feed, may have to go until the OD is supported.


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