tapered mill bore
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    Default tapered mill bore

    I have an aluminum part, has a 20mm bore thru 1.17" material.

    I'm trying to mill bore to finish size for a bushing, but the bore tapers from top to bottom.
    I'm going around twice for a spring pass.
    I'm using a 3/8 x 1-1/4loc 3 flute carbide endmill.

    I would rather not add a reamer or boring head to this but it just isn't consistent.

    What am I not thinking of?

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    I always roughed with a helical pass and finished with a regular pass.

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    I'm drilling it to 19.5mm diameter and then milling.

    Does that change anything?

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    Quote Originally Posted by Houndogforever View Post
    I'm drilling it to 19.5mm diameter and then milling.

    Does that change anything?
    You wouldn't think so. Maybe the end of your cutter is dull?

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    Quote Originally Posted by Houndogforever View Post
    I have an aluminum part, has a 20mm bore thru 1.17" material.

    I'm trying to mill bore to finish size for a bushing, but the bore tapers from top to bottom.
    I'm going around twice for a spring pass.
    I'm using a 3/8 x 1-1/4loc 3 flute carbide endmill.

    I would rather not add a reamer or boring head to this but it just isn't consistent.

    What am I not thinking of?
    Worn or tapered end mill, cutter run out.Cutter pushing off
    Tony

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    Quote Originally Posted by Mark P. View Post
    You wouldn't think so. Maybe the end of your cutter is dull?
    Test it on your fingernail

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    When I have problems with taper like that I usually have good luck running the finisher as a helical path.

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    We don't know the fixturing, the specific material (aluminum covers quite a range), the toolholding, the spindle/machine configuration, the speeds/feeds you're currently using, the coolant, the cutter condition, why you're not using a larger diameter endmill, whether you could use a stub reamer/home made boring bar with an insert to set diameter, the taper amount, the tolerance you're shooting for, the phase of the moon, and whether your shop rests on ancient Indian burial grounds.

    Aside from that, I can comfortably conclude that you're running the spindle backwards. Reverse rotation to CW, and you'll be spot-on.

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    I got a curt 5 inch vise clamped into an old bridgeport vise hanging off the side of a chinese copy of a bridgeport mill with a hot copy of centroid system running on a virtual Linux machine.
    I'm using an old high speed steel left hand cut, right hand spiral endmill running at 92 sfm and .012 IPT.

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    ok, so actually it is on the Speedio rotary holding a 1/2" 2-clamp raptor dovetail clamp. 6061-t651 extruded bar.


    I'm using the 3/8 end mill because going much larger and the interpolated bore starts losing shape when the actual movement ends up being a 1/8" dia circle.
    I'm using a 1-1/4 loc mill as I need to reach 1.17 thru the part.

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    Quote Originally Posted by Houndogforever View Post
    I got a curt 5 inch vise clamped into an old bridgeport vise hanging off the side of a chinese copy of a bridgeport mill with a hot copy of centroid system running on a virtual Linux machine.
    I'm using an old high speed steel left hand cut, right hand spiral endmill running at 92 sfm and .012 IPT.
    Well there's yer problem right there - I always use 94 SFM with that setup. But watch the cutter TIR, anything less than .005" and it howls like a banshee.

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    More seriously, it sounds like there's a lot of "stuff" in the holding path, which means a lot of opportunity for movement. I'd ditch that 3/8" full flute endmill and use a short-flute necked EM, with a helical cut to final size.

    Something like this: 3/8"DIA. 3 Flute SE HP Carbide End Mill Necked 37 Degree Helix | eBay but of the appropriate reach. YG-1 makes a range of them, and Suncoast is a good vendor. I just grabbed that link because it was the first.

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    Quote Originally Posted by Booze Daily View Post
    When I have problems with taper like that I usually have good luck running the finisher as a helical path.
    ^^^^^^ this

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    Quote Originally Posted by Houndogforever View Post
    I got a curt 5 inch vise clamped into an old bridgeport vise hanging off the side of a chinese copy of a bridgeport mill with a hot copy of centroid system running on a virtual Linux machine.
    I'm using an old high speed steel left hand cut, right hand spiral endmill running at 92 sfm and .012 IPT.
    NO WONDER it is running so poorly! lol

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    Another vote for helical interpolation for the finish path.


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