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how much bigger does a drill bit drill?

Discussion in 'A BEGINNER'S FORUM (Learn How To Machine Here!)' started by Rcdizy, Aug 11, 2017.

  1. benmychree

    benmychree United States John York H-M Supporter-Premium

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    I think that the set that I bought was Eastern European, probably bought from KBC Tool; that was probably 10 years plus ago, the way time flies, likely more like 15 years. That set came in a wooden block, like the Shars set pictured; I made hardwood blocks for all my chucking reamers and taps larger than machine screw sizes.
     
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  2. Silverbullet

    Silverbullet Active Member Active Member

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    There are ways to make a drill bit drill bigger or smaller. By varying the cutting edge length and width plus off center of the tip. As for you hole being tight you can freeze the liner and press in or set in when it warms up it'll be tight . But it's up to you. Lots of ways to get the job done. The norm is spot drill and ream to size. Amount of most press fits on liners is .0005 to .001 . If I remember right.
     
  3. Bob La Londe

    Bob La Londe United States Active Member Active Member

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    How much over does it drill? It really depends on a lot of factors. Runout, speed, technique, length, type of grind, setup. I've got a few sets of modestly expensive stub length screw machine drills that only get used when a hole has to be "pretty good." With good technique they drill holes that are pretty good. When a hole has be nearly perfect in size a reamer is ok, but for small sizes it still won't be any straighter. It will follow the hole you drilled. Chucking reamers tend to be long and flexible. A reamer is not intended to straighten a hole. A spotting drill followed by a a short properly ground screw machine drill followed by a reamer is going to get you as close as you can under most circumstances for small holes. For anything large enough boring will get you very close as well, but you will still have some variations due to the tool geometry, tool flex, and machine guality depending on technique.

    One might argue that you can't get reamers in all the sizes you might like, but for the most part you can. They just cost a lot. Outfits like Harvey Tool make small chucking reamers in decimal sizes to cover a huge range. Some outfits will even make custom reamers (or mills) for you.

    One thing to be aware of is a reamer ONLY sizes a hole. It doesn't do anything else, and if runout or offset is bad it can make the hole oblong or bell shaped. I believe this is why they tend to be long and flexible. So they can flex to follow the hole. If you leave it in the hole to long spinning it will still over size the hole. I ran into this problem making brass micro end mill adapters yeas ago. Gunsmiths run into this problem when chambering rifle barrels. The answers is a floating reamer holder. You still need to only have it spinning in the hole the minimum amount of time to size the hole, and not any longer.

    To the original poster. You already have a slightly oversize hole in a part I assume is otherwise finished. If your tolerances for the pin position will allow it just glue it in with some Loctite sleeve and bearing locker. They make atleast one formula that is intended to fill small gaps. Your local hardware or auto parts store may not have them, but you can always order it from somebody like MSC or McMaster. Maybe even Zoro. If your are confident in your hole position and it needs to be more precise just turn a pin out of some over sized stock and press it into the hole. I sometimes wind up with oversize holes for one reason or another. Usually my own carelessness. I'd rather spend ten minutes making a custom pin than half a day remaking a part.
     
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  4. jlsmithseven

    jlsmithseven United States Active Member Active Member

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    In my experience so far, drill bits drill bigger for me because:
    1. They're not in a collet ring. Whenever I tried a chuck or anything else to hold it, they usually drill larger.
    2. The hardness of the material matters. Speeds and feeds as well.
    3. Don't chuck up too far or too little on the drill bit. Right around the end of the flutes should be good.
     
  5. mmcmdl

    mmcmdl H-M Supporter - Premium Content H-M Supporter-Premium

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    Do what us old timers do when necessary . Smack that oversize hole with an appropriately sized ball bearing and load it up with Loctite retaining juice . No-one would ever know the difference ! ;)
     
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  6. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    Good idea, but never admit doing it... :busted:
     
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  7. mmcmdl

    mmcmdl H-M Supporter - Premium Content H-M Supporter-Premium

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    Who ? Me ? :big grin:
     

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