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Thread: accuracy drilling small holes

  1. #1
    Join Date
    Sep 2006
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    Southwestern Ontario, Canada
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    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
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    Jul 2007
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    Earlville PA
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    Default

    Chuck run out maybe? Stu

  3. #3
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    Peralta, New Mexico USA
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    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
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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.

  5. #5
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    Jun 2004
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    Spindle run out.
    Chuck run out.
    Small drill was never straight to begin with.

  6. #6
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    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

  7. #7
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    Sep 2009
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    Center punch!

  8. #8
    Join Date
    May 2006
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    Are you using jobber drills? if so then try precision drills that are much shorter and don't wonder as much, the quality of the drill is very important too...

  9. #9
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    First, tram the head to the table as exact as you can make it. Use a collet for the spot drill instead of a chuck. Use a quality small chuck with low runout to hold the drill. Use a good quality sharp bit and good cutting fluid. Use a light touch and let the drill do the work. If you push too hard, it will go off center.

    Peck drilling won't make the drill go any straighter,but you have to do it often to clear the chips. Otherwise, the chips will lock up the drill bit and break it off in the hole.

    I drill #57 (.043) bits 3/4" through steel by the hundreds and have them come out the other side on location doing it this way.

  10. #10
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    I think you're not getting a proper cone for the drill to start in. It could be various reasons as noted above. We have to assume a proper drill grind, and, once a drill is mounted, run out of the chuck doesn't matter (it may however matter when using the spot drill).

    Of course if you are boring afterward, its not an issue...but that's a little challenging if you need a 1/32 hole.

    Two practices in watch making worth noting. They might be useful techniques but they underscore the importance of a cone in the right spot for the drill to start. With lathe work, it is common to make the starting cone by hand with a graver (but its not easy to consistently avoiding getting a pip!). Drilling is done by hand with a pin vise. Point being with a single point tool (graver) you're guaranteed to get the cone in the right spot, and with the start in the right spot, exactly where the drill is held is minor....and they don't rely on the tailstock to get the starting position. Secondly, on a watch makers jig borer, a very accurate centre punch mark is made and that is used to start the drill. We're talking machines who's dials are graduated in tenths so its done to a very high level of accuracy. all the punch marks would be made with a special quill and then each would be align via a microscope for drilling/boring.

    That's a couple of ways small holes (sometimes a few thou) get located properly by those who must get them accurately placed. The takeaway is what matters is having a cone of the right shape in the right spot. I'd start by looking at the cone you're getting with a loupe or microscope and go from there.
    Last edited by Mcgyver; 02-09-2019 at 01:23 PM.
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