Drilling with endmill in drill chuck?
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  1. #1
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    Default Drilling with endmill in drill chuck?

    Hey all, I know it's a big no-no to use an endmill in a drill chuck, and understand the radial forces that a drill chuck isn't designed to handle. However, I have a case today where I need to use a 5/16" endmill to drill a hole and didn't realize it, but don't have any collets or endmill holders in that size. I checked my bin for a 5/16 EM with a 3/8" shank and don't seem to have that either. Other than the fact that a drill chuck doesn't grip like an endmill holder, is there still a reason not to drill with an EM in a drill chuck?

    My internal reasoning is that I won't miss the extra grip of an EM holder or collet, because the metal removal is going to be less than a 5/16" drill, since I'm going slow, so since obviously the chuck has the bite to do one, it should still be ok with the other.

    The other thought is that since runout in a chuck is more than an EM holder or collet, maybe it'd be hard on the EM since it'd be taking uneven bites. However, I don't know if an EM is a lot frailer than a drill, and drills survive slightly uneven bites on their two sides just fine all the time (when slightly improperly sharpened for example, although in that case they don't drill straight, but it doesn't hurt the drill.)

    I'm doing this in a mill, not a DP.

    So that's the general question, and I kind of think the answer is "probably no big deal."

    However, in this case, the *reason* I need an endmill instead of a drill is that I'm putting a hole off-center in a ball, so a drill would skate out of the cut (I even spotted it first, and a drill still moved.) So given this condition, maybe, even though I'd be EM-drilling straight down, I *do* still have radial forces for that first second where the EM is biting on one side and not touching on the other, until it creates a flat - and then after that no radial force. So maybe even those who say the general case above is ok, would still say this arrangement has the potential to damage the chuck in this specific situation?

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    Take some round stock, make a split sleeve, and use a collet. There's places where you can get away with using a drill chuck and an endmill, this isn't one of them.

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    Quote Originally Posted by Milland View Post
    Take some round stock, make a split sleeve, and use a collet. There's places where you can get away with using a drill chuck and an endmill, this isn't one of them.
    This, if you do it quick and dirty that is a 5 minute job.

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    Perfect. Thanks!

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    Though I agree making a bushing to use the end mill in a collet or endmill holder with a set screw especially to do what the OP intends but 5 minutes?? You sound like some of the workers at my customers place

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    Quote Originally Posted by Froneck View Post
    Though I agree making a bushing to use the end mill in a collet or endmill holder with a set screw especially to do what the OP intends but 5 minutes?? You sound like some of the workers at my customers place
    Well, now that I'm done, I can confirm the 5 minute estimate was correct - but only because I spent the 5 minutes digging through my bin of old endmills and did find a slightly sharpish 5/16 that had a 3/16" shank for the collet I did already have, haha...

    Someone might be able to make that in 5 minutes, but I'm not that fast! (Although he did say split, so I don't think he was talking about a set screw? I was envisioning drill/ream to 5/16 ID, use a hacksaw to split almost down the whole length of it twice, and let the collet squeeze for the grip.)

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    Quote Originally Posted by JasonPAtkins View Post
    I was envisioning drill/ream to 5/16 ID, use a hacksaw to split almost down the whole length of it twice, and let the collet squeeze for the grip.)
    Yeah, that's generally what I meant, but we usually do a single, full cut down one side as it works fine that way.

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    End mill is sharp on the OD so will/may cut a larger hole..
    A drill often cuts oversize double the amount the point is off center.
    But the drill will cut like a reamer to a few tenths over the micrometer size if the hole is pre-drilled a size a tad smaller than the need size drill.. perhaps a 1/32 or so. Yes the drill may try to catch so a very slow in-feed is best.

    But looks like job is done , Good.

    Doing a lot of this kind of work a screw hold end mill holder perhaps 3/4 (or any) Id can be used with a 3/4 (or what) od slug in the hole made to the size you need to hold....drilled to the size you need can be handy for all odd cutters/drills,

    You can use the actual drill for drilling the slug (with a pre-drill)..Very handy method for MM tooling you may not have a collet for.

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    I make a few of those bushing for different sizes simply because the SPI quick change I have for my 40 NMTB ToolMaster mill. Many carbide endmill shanks come in the size of the cut diameter plus metric end mills will not fit any of my tool holders and I can't find any that are! So I'm stuck making bushings. I usually chuck some tool steel that is larger and turn the OD to size, then drill and bore The ID to keep it concentric. I do split it with a hacksaw and deburr the cut with a 3 sided file. The tool holders are set screw type so some especially the larger ones I don't split and cut a slot so that the set screw hold the endmill on the flat notch. I have no problem with size, 2 flute endmill cuts to sizs if it runs concentric. I also have a Darex drill grinder, does a great job on drills but I uses endmills in similar applications to the OP. Of course it take me longer than 5 minutes, 6 minutes comes to mind But that was just to think what I was going to do Then I do it

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    End mills are harder than the drill jaw chucks. Drills have soft shanks to the
    chuck jaws can bite into them.

    If you spin the end mill in the chuck it will toast the jaws to some degree.

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