Drilling a straight hole
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    Default Drilling a straight hole

    I am trying to drill a barrel nut for the gas tube and can't get a straight hole. Hole is .200"

    I've been trying different methods after scrapping this part, tight pilot hole undersized pilot hole, multiple length drill bits, power feed, manual feed, peck every 50 tho ... I've used new drill bits and freshly sharpened drill bits. Pilot holes were done with a 4 flute end mill. I don't have a little boring bar (yet) or a reamer in this size.

    Suggestions appreciated.
    Attached Thumbnails Attached Thumbnails 748737051_20211123_143231_2878500_resized.jpg   748610843_20211123_144045_2981924_resized.jpg  

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    Do the drilling on a lathe. Use a quality sharp drill bit about 5 thou. under, Ream with a sharp! three flute ream.

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    Quote Originally Posted by CalG View Post
    Do the drilling on a lathe. Use a quality sharp drill bit about 5 thou. under, Ream with a sharp! three flute ream.
    That's four setups plus the work to make prick marks for setting up on the lathe :'( I have considered it

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    Buy the correct self centering carbide drill.
    Clock it in to ensure zero runout.
    Coolant and peck by hand.

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    Drills ate so thin webbed it is not uncommon that they may not drill straight, Drilling a second size rarely will help.

    Reamers with a much thicker web and often may flutes make straight close size holes.

    A local grind shop can make a .200 reamer from a near size standard, likely making it .1998 to finish at .2000

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    Reamers flex just like the drills - hole will be to size, but not necessarily straight. Carbide drills, like was recommended may do better due being more rigid. But ultimately boring is the only way to get it straight.

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    Not that it should make a difference
    Are you drilling the 4 holes before or after the inner detail?

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    Drill from the fussy side first. Consider drilling from each end.

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    Do you have to do one or a million?

    Its not hard to do this the tedious way (I've done it several times and get a hole within a thou or 2 over 25x the diameter) for a couple but its not suitable if you have a lot of them to do

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    Quote Originally Posted by scott-ak View Post
    I am trying to drill a barrel nut for the gas tube and can't get a straight hole. Hole is .200"

    I've been trying different methods after scrapping this part, tight pilot hole undersized pilot hole, multiple length drill bits, power feed, manual feed, peck every 50 tho ... I've used new drill bits and freshly sharpened drill bits. Pilot holes were done with a 4 flute end mill. I don't have a little boring bar (yet) or a reamer in this size.

    Suggestions appreciated.
    It ain't the right thing to do but a couple of times in similar situations I have cut the shank of the drill off so I can choke up on the drill to where there is just barely enough sticking out to do the job, it is harder for it to wonder when it is really short.

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    Nachi 3 flute aqua exoh3f carbide drill. Centers with precision and the extra flute will generate a finish and concentricity that rivals a reamer.

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    Is it just me or do you first need to define 'straight'?

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    By the way. BTDT

    Done on the mill, drill while indexed on the dividing head. (no prick marks ;-) Spot drill, twist drill, ream. And still a few of the holes don't work.

    ar10 Actually
    lr 3OH8 ;-)

    I'm not proud, but it's light(er) ;-)img_20211124_230504811_burst000_cover_top.jpg

    Oh! and a note on tooling. ER 32 collets are the tits! hold anywhere up the length on spiral flutes.
    Attached Thumbnails Attached Thumbnails img_20211124_230504811_burst001.jpg  

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    Quote Originally Posted by GregSY View Post
    Is it just me or do you first need to define 'straight'?
    Kinda wondered about that myself. Is that second picture of the start end or the exit end?
    If it's the former the OP needs a better way of laying out the holes.

    What do the holes do? What's the spec on the drawing? If there is one...

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    Quote Originally Posted by LKeithR View Post
    Kinda wondered about that myself. Is that second picture of the start end or the exit end?
    If it's the former the OP needs a better way of laying out the holes.

    What do the holes do? What's the spec on the drawing? If there is one...

    The NUT retains the barrel to the upper receiver. The holes allow the gas tube to pass the nut and enter the upper receiver and BCG.

    Also the holes serve for wrenching the nut tightness. Unless external flats are also part of the element features.

    Through holes are not neccessary for all hand guard configurations, but ......

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    Two thoughts:

    The material: could it be due to pockets of harder or softer metal? Have you tried another alloy?

    I would try a solid carbide, center cutting end mill that is a bit undersized. 3/16" (0.1875") or 5mm (0.1968"). Then finish with a reamer to the final size.

    A pilot hole at 5/32" drilled with a solid carbide bit would clean out most of the material first, making the job of the end mill easier. I don't think it would wander enough to get outside of the 0.2" final diameter but you may need to use a smaller one if it does. If this is used first, the end mill does not need to be center cutting.

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    Quote Originally Posted by EPAIII View Post
    Two thoughts:

    The material: could it be due to pockets of harder or softer metal? Have you tried another alloy?

    I would try a solid carbide, center cutting end mill that is a bit undersized. 3/16" (0.1875") or 5mm (0.1968"). Then finish with a reamer to the final size.

    A pilot hole at 5/32" drilled with a solid carbide bit would clean out most of the material first, making the job of the end mill easier. I don't think it would wander enough to get outside of the 0.2" final diameter but you may need to use a smaller one if it does. If this is used first, the end mill does not need to be center cutting.
    The barrel not can easily be 1.5 inches in length. that's an L/D of 7.5 .. That sort of end mill might be difficult to source. Especially in carbide.

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    thanx for sharing your work. Two of the holes work but if you look close you can see where one of the other holes broke thru the threads

    I found Guhring has carbide 3 flute straight shank bit in 5.2mm and some say they work well.
    Attached Thumbnails Attached Thumbnails 1030090603_20211123_144249_2916388_resized.jpg  

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    Quote Originally Posted by scott-ak View Post
    thanx for sharing your work. Two of the holes work but if you look close you can see where one of the other holes broke thru the threads

    I found Guhring has carbide 3 flute straight shank bit in 5.2mm and some say they work well.
    Guhring makes damn good drills and there is plenty on Flebay usually!

    Murf


    Sent from my iPhone using Tapatalk

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    Awful deep hole for a regular twist drill. Must be pushing 4 inches or so?

    Deep hole... Tight tolerances...

    Maybe a gun drill would be better suited to this work?

    Else maybe redesign the part to eliminate the need for through-holes? Mill slots for a claw wrench/outside pin wrench instead?

    Cheat and drive a golden spike in the middle of the hole?


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