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Thread: hole sizes

  1. #1
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    Question hole sizes

    A heated debate is going on at another forum (no, not THAT one ) about hole sizes. It seems that one faction believes that a given drill will make a different size hole in some materials than others.
    I'm dubious having never had a problem between materials, I don't buy this argument.
    What say the jury?
    At the same time, some believe that drills vary between brands. Again, I haven't ever experienced problems with this issue and don't buy into that argument. What say the jury about this?
    Next week, I'm going to do some tests with materials and measure drill bits from a variety of sources. I expect the variations to be almost zero.

  2. #2
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    How precise to you want to measure it? If I remember correctly you will get some variation from drilling say Aluminum to steel. But you are talking VERY small amounts. Much smaller than we care about in wood working. I would expect that would translate into the some difference in soft wood and hard wood. But nothing of a practical difference. Woodworkers have in the past few years started trying to measure to machine tolerances which is overkill on wood IMHO.

    Difference from drill brands. Nope, unless you buying really cheap poorly made bits.

  3. #3
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    I don't believe that the material that is being drilled has any effect on the hole size. I have done machine shop work for a few years and have found that a given bit will drill the size hole that the bit is. However if you sharpen the bits freehand and you are not careful to get the web centered correctly the bit will run out a small amount giving you a slightly larger hole. This has been my observation over the years, I have not noticed the brand of bits making a difference, but this being said, we always used a good name brand of bits and not the cheaper Chinese variety.
    Charles

  4. #4
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    I can see 2 reasons why hole size could vary. If the material fails by crumbling before it is cut is the first one. Think spruce, perhaps balsa - some of the end grain material is pulled out rather than sheared. It clings to the bit, making it oversized. I think this might also occur in white metal.

    The 2nd reason is a combination of operator error and/or dull bits. A dull bit wants to wander. If it's not securely chucked in the drill press or if the stock is not clamped in place you'll get an odd-shaped hole.

    I look forward to your results mic'ing drill bits. If you find a variation that's significant to woodworking I'll be surprised.
    All the best,
    Ian G

    **Now holding auditions for a catchy new signature**

  5. #5
    Hole sizes DO VARY, on wood or metal. Worked in machine shop for 17 years, working with metal. (Jig Grinder)
    feeds, runouts, metals. All drilled different. Use to keep a log on different information.

    Use to work in.0001, you read right 4 place demical. Talk to my foreman when I would miss the whole size about .00015. Parts would actual be scrap, 5 place demical. One time proved to him that you can hold a part in your hand and change the tolerance of a hole.

    It was a bear many times from one operation to the next to maintain that kind of tolerance.
    With metals, had to wait till the machine was warmed up. In fact it had a tempature guage on the machine and would wait till it got to temp.

    As the day progessed would have to change speeds, feeds, to keep the tolearace.

    This applys to woods from soft to hard wood, from soft to hard metals all this depends on:

    1.) Speeds: My machine would be electric and AIR. Could change the hole size with how much air would allow the head to spin at. Slower the speed tighter the hole, with same bit.

    2. Feeds: how fast you pull down on the handle. Use to have the machine where could set how fast it went down into the metal, from slow, medium or rapid plunge, would make differant holes using the same size bit.

    3. Metals, wood. There are tons of different grade of metals, just like there are different woods.
    These will also have a bearing on SPEEDS, FEEDS & MATERIALS. Softer materials the hole tends to run larger, because there is no side pressure, on harder materials tend to cut smaller.

    4. Good VS Bad bits.
    To answer this, would be "YOU GET WHAT YOU PAY FOR" I can take cheap bit and melt it like butter, and take a cheap bit VS expenive bit and come up with different hole sizes.

    Many wood workers believe it or not their hole sizes vary, but will not to be noticed. But use to have guages and could prove to you that your holes do vary, not enough for you to notice ...........BUT THEY DO!!!!

    Can take say 1/2 drill bit and can come up with different size holes on wood or metal...........come over and I'll prove it.
    Last edited by Bob Spare; 12-24-2006 at 05:23 PM.

    WoodWorking, Crappie Fishing, Colts, Life is good!

  6. #6
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    Thanks Bob, I was not a machinist but I worked with and around a lot of them and in a manufacturing environment for many years working with cutting tools. You reminded me of a lot I learned listening to the guys but had forgotten.

    Quote Originally Posted by Bob Spare View Post
    Use to work in.0001, you read right 4 place demical. Talk to my foreman when I would miss the whole size about .00015. Parts would actual be scrap, 5 place demical. One time proved to him that you can hold a part in your hand and change the tolerance of a hole.
    I remember a machinist talking about having to make some pins that where the tolerances were something like +/- .0001. Checked the pins and one was something like .0001 undersized. He said he took it and held it in his hand while the QC guy measured the others. Then asked him to remeasure the one that he had in his hand and it was in tolerance then. Always remember that story.

  7. #7
    Not trying to capture this thread.....but I want too learn as well as give. Just happened that the right subject pot up that I had experience in over the years.

    If I just could get as good at wood working as I was journman machinist I would have it made.
    I am learning!!!!!!!
    Never too old to learn (72)

    WoodWorking, Crappie Fishing, Colts, Life is good!

  8. #8
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    In the machine shop world, even a perfectly sharpened, top quality drill bit will cut oversize, particularly in hard metals like incolnel, hastelloy, tungsten, etc. There are tricks to make a twist drill cut undersize but if youíre working to close tolerance work you will use a reamer or if youíre working to very close tolerance work like Bob, youíll finish the hole on a jig grinder (spent a few years on a Moore #3)
    Iíve never experimented on various woods but I would imagine they would cut a little oversize as the drill point wanders around in the grain, particularly smaller sized bits.
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  9. #9
    As a machinist that works to .0001 or better I can tell you that different materials will make the same drill bit change diameters. At the same time, chuck the very same drill bit in a different machine and due to run-out and wear of the machine, you will get a different hole diameter.

    At Lie Nielsen they had a special program for their cnc machines during breaks and lunch. It would basically cycle the machine through all the functions when the operator was gone, that way the machine would stay the same temp and would not throw things off. When I mean off, we are talking 40 times smaller than a human hair!! In woodworking, precision does indeed matter!!

    Heck when I worked for LN I once saw a .150 drill bit screw up a lot of planes. The bit was actually .150 and not .002 oversized like most drill bits there.

  10. #10
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    Quote Originally Posted by Travis S Johnson View Post
    ... not throw things off. When I mean off, we are talking 40 times smaller than a human hair!! In woodworking, precision does indeed matter!!
    Please clarify. Are you talking woodworking or toolmaking tolerances? I would hate for any newbie to think that their work needs to be within a 10,000th. Aside from the fact most of us can't measure that fine, I think (just my opinon) that there's a bit too much emphasis on extreme accuracy - machine shop type accuracy. I'd hate to think of anyone throwing their hands up in failure because they can't do better than +/-1/64th.

    To relate back to the original post - garden variety fractional bits have never let me down in woodworking. Poorly sharpened spade or brad point bits have caused me problems, but that was my fault for using them in that condition.

    Wood moves and no degree of accuracy is going to change that.
    All the best,
    Ian G

    **Now holding auditions for a catchy new signature**

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