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Thread: accuracy drilling small holes

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  1. #1
    Join Date
    Sep 2006
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    Southwestern Ontario, Canada
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    5,175

    Default accuracy drilling small holes

    I have brought this subject up before with out any final conclusions but I have dug the hole deeper.

    When I drill small holes, under 1/16" or so, the holes NEVER end up where I want them IE: in the center between to edges etc., so I did some additional testing. If I need a 1/32" hole right in the middle of a square or round bar they inevitably come out 5 to 10 thou off center now if I use an end mill to drill the hole they will be within 1 to 2 thou of the center. I consider that acceptable with my cheap Chinese mill, cheap Chinese collets and cheap "unknown" end mills all of which could be considered to be of questionable accuracy (maybe better then I thought).

    So it would seen that the problem is using drill bits. I always use a spot drill or a center drill (for small holes) thinking that it would place the holes where I want them to be. Apparently not so. Some times the center drill/spot drill holes have a pip in the middle but not always. The question is how do you guys get holes to come out on or near the place you want or in other words how do I get the damn drill bits to go straight.

    P.S. I always peck drill, which is suppose to help, the holes to stop the bits from bending instead of driving them down with all my strength.
    The shortest distance between two points is a circle of infinite diameter.

    Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

  2. #2
    Join Date
    Jul 2007
    Location
    Earlville PA
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    323

    Default

    Chuck run out maybe? Stu

  3. #3
    Join Date
    Mar 2005
    Location
    Peralta, New Mexico USA
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    918

    Default

    Holes from a drill can be accurately placed, accurately sized and accurately round. Just seldom all 3 at the same time.

    Drilling removes material quickly. Boring locates a hole well. Reaming tends to give you a hole to the desired size and roundness. If you need holes on position, straight and on size you really have to drill to remove most of the material, bore to locate and straighten the hole and ream to take it to size.

    If you only need to get close enough you can spot drill to start the drill. This improves the starting position quite a bit. If you don't need to be that close you can start with a split point drill, they tend to not wander as much as non-split points. If you're starting on material at an angle to the drill point (or round stock even if you're sure you're on center) it helps a lot to put a flat with a center-cutting endmill before spotting.

  4. #4
    Join Date
    Jun 2004
    Location
    N.J.
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    1,415

    Default

    Spindle run out.
    Chuck run out.
    Small drill was never straight to begin with.

  5. #5
    Join Date
    Jan 2007
    Location
    Minnesoa
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    Default

    Hi,

    First, the old "drill, bore, and ream, mantra does not work for tiny little holes. The biggest issue when drilling tiny holes is lack of enough spindle speed I have found. That and wanting to drill 3" deep.

    Few drill presses and mills can provide the proper speeds needed to consistently drill a straight hole under 1/8". You need 5000+rpms to really have a good shot at it.

    So what can we try since few of us here don't have a 10,000rpm spindle handy.

    If you need to drill a perfect #60 hole 2" deep in stainless, you need to rethink just what it is you are doing. Ain't going to happen in your average home shop.

    Consider using a stiffer tool. When the holes get below 1/4" and the roundness, location, and straightness matter, I toss the HHS and use solid carbide drills. Expensive, but when it matters, good results costs money. I've had very good luck with solid carbide spade drills if the holes aren't stupidly deep. Though fluted carbide drills are definitely better than HSS.

    If the hole isn't seriously deep, using an endmill can also work if you can get a pilot hole in the piece. Again, endmills tend to be stiffer than drills.

    If you are really up the creek, then your best option might to plunge edm.
    If you think you understand what is going on, you haven't been paying attention.

  6. #6
    Join Date
    Jan 2014
    Location
    Edmonton Alberta
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    1,315

    Default

    I assume the pieces your drilling are small,this drill jig is pretty accurate.The smallest I've drilled is 1/16" and seems to keep drill in place.The smallest collet I have 1/32" but have not used it yet,my drill press only goes to 2800 rpm.

  7. #7
    Join Date
    Jan 2010
    Location
    Kansas City area
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    5,597

    Default

    The small drills will still cut at any rpm, you just have to feed accordingly. I have drilled small holes just fine at 500 rpm. The recommended rpm is for a production setting where you need to make the best time.

  8. #8
    Join Date
    Jan 2009
    Location
    Nordland, WA
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    If there is a pip in the middle of your center/spot drill marks then you have some significant run out and/or looseness in the spindle/quill somewhere. This assumes your center/spot drills are properly sharpened.

    Pete
    1973 SB 10K .
    BenchMaster mill.

  9. #9
    Join Date
    Jan 2004
    Location
    Missouri
    Posts
    30,401

    Default

    Quote Originally Posted by 10KPete View Post
    If there is a pip in the middle of your center/spot drill marks then you have some significant run out and/or looseness in the spindle/quill somewhere. This assumes your center/spot drills are properly sharpened.

    Pete
    maybe.....

    Most larger drills make a significant flat spot in the center, where the drill fails to cut, and only rubs off material, due to the way the drill "point" is made. Even spade drills can be like that. You need a spot drill smaller than the small drill. A center punch mark "usually" works pretty well for small drills

    A small drill will skate around on that flat spot and get several thou off at least. Spot drilling works best when the spot drill is actually smaller than the follow drill.
    1601

    Keep eye on ball.
    Hashim Khan

  10. #10
    Join Date
    Sep 2009
    Location
    Sacramento, CA
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    1,222

    Default

    Center punch!

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