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  1. #1
    meco3hp is offline Hot Rolled
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    Hello,
    What is a "Flat Bottom" or "Bottoming" drill bit used for? Could a person resharpen them to have a 118* tip on them and just use them as you would a regular bit? A buddy of mine came up with 2 of these, in a bucket at a farm auction, new in their boxes!

    Thanks!
    Richard

  2. #2
    traytopjohnny is offline Stainless
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    Nah! You can cut a flat bottom profile, do what you need to do and then turn right back around and put a driling point and return it back to it's original purpose. John

  3. #3
    gvasale is offline Hot Rolled
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    much nicer on sheet metal. I saw someone using them on sheetmetal about 10 years ago. Try one this way and let me know what you think. of course, they can't have a perfectly flat bottom. Suitable for drill press or mill only as I recall.

  4. #4
    Bill's Machine Shop is offline Hot Rolled
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    I didn't know they even had a name for it. When I worked in a job shop, I'd grind bits for cutting through thin sheet metal as close to flat on the point as I could. I'd leave a little point in the center to keep the drill from drifting. In use, the bit would remove nearly all the metal before it broke through and augered into something I didn't want to damage. It worked really great and gave a lot better control of the drill, even when hand-held.
    A flat pointed (I see the makings of a new oxymoron here) bit will also work well if you build furniture. It's much easier to determine depth for a dowel hole and reduces risk of drilling a hole through a surface you don't want to damage. WWQ

  5. #5
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    At my last job, we had probably fifty twist drills, some over 2", ground for either a dead-flat-bottom profile or a near-flat-bottom. These drills were mostly used as custom sized counterbores.

    For counterbore use with a socket head cap screw, the hole bottom must be dead flat. Just a little difficult to grind, as both flutes have to be 90 to the body. Drill the clearance hole for the cap screw first, followed by the flat bottomed counterbore. Slower is better, as there's no center point to guide the drill body. Once the counterbore is fully below the surface, the feed can be increased.

    Near-flat-bottom drills are a breeze to grind and use. Set the protractor or drill guage to 100 and grind a normal profile. This makes a point with an included angle of 160. Even this tiny angle makes a huge difference, as the drill now has a point & tries to self-center on the clearance hole. These drills can be run twice as fast as the dead flat profile.

    For sheet metal use, there are better choices. My favorite is the Uni-Bit:



    ---------------
    Barry Milton

  6. #6
    jims's Avatar
    jims is offline Cast Iron
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    You should state what size they are. Someone here
    might be looking for just that size. I grind my own but some have never learned that skill.
    jims

  7. #7
    BadDog is offline Stainless
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    Sheet metal drills are not really "flat", but rather more like a trepanning tool so that the ends of the cutting edge are the first to make contact.

    On using drills for countersinks, I did that with a drill not to long ago and it is a pain to sharpen. Mine was really only cutting on one side, but it didn't matter, because I drilled most of the hole with a normal drill bit and then only needed to flattened the bottom. I would never attempt to start a flat drill bit with my drill press. I could probably get away with a stubby or screw machine bit in my mill, but not on the drill press.

  8. #8
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    If the drill press weighs 10,000# (Morse MorSpeed, 5MT, 48" arm) it isn't a problem

    ----------------
    Barry Milton

  9. #9
    JST's Avatar
    JST
    JST is offline Diamond
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    The old-time shop books explain about those.... just for flattening the bottom, i.e. for a hole where the bottom must be flat, like a really deep counterbore, except that the end need not have a hole continuing.

    You have to have the hole first, because they will obviously not start a hole with out wandering from here to Tasmania.

    One book basically says "it's an end mill". Seems good to me.

  10. #10
    northernsinger is offline Titanium
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    Photographic example of item under discussion, 13/16ths:


  11. #11
    JST's Avatar
    JST
    JST is offline Diamond
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    You sure that isn't a "hammer"?

    I'm just lookin' at all the dings on the taper.

  12. #12
    northernsinger is offline Titanium
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    A good 'point,' W4.

    I bought a couple hundred pounds of drills from the iron works my family had a part of, when they closed down, in 1985 (after it had run 150 years, fronm 1833). This was one of them. There weren't any machinists there, only iron workers, mainly Polish and Jewish.

    Those workers managed to help that firm pay its bills for a good many years. But maybe to some there it was a hammer.

    Not the best example of care of consumables.

  13. #13
    moe1942 is offline Aluminum
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    Maybe I missed something but why not use an end mill. That's what I have done in the few instances that I needed a flat bottom blind hole.

  14. #14
    willbird is offline Banned
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    Moe, most end mills do NOT make a flat bottom hole, AND for the job at hand we really would rather the tool pilot in the hole already there and not cut all along it's sides like an endmill does . Also if your 2" deep with a 1/4" hole, a flat bottom HSS twist drill is a LOT cheaper than a 2" LOF endmill

    Bill

  15. #15
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    why not use an end mill
    That's a valid question. If this operation was being done in a large milling machine (40 taper or 50 taper), an end mill would be a good choice.

    Lots of flat-bottomed holes are needed while hole-making on the drill press. It's near impossible to find a large end mill with (for instance) a 5MT shank, which is common on a large drill press. So you grab the drill size needed, cut off flat in the abrasive chop saw, grind relief behind both cutting edges, and you're ready to go.

    I'm just lookin' at all the dings on the taper.
    Where I last worked, that drill bit would be considered pristine, given a score of 10 out of 10

    In a production shop, expendable tooling is just that - use it hard, use it til it's all gone, get another to replace it. Grab a 1" bit with a 3MT shank, put it in the 3MT-5MT adapter, whack the end of the adapter HARD on the drill press table (or lathe compound, or on the top of a thick metal bench), drill hole, wedge the adapter off (which often sends the bit to the floor) & drill something else

    Pretty tooling doesn't pay bills, but lots of holes, drilled in a timely fashion, pays the rent... and a busy shop drills dozens, sometimes hundreds of holes per day. You don't get yelled at for breaking the occasional bit, or putting dings on the taper -- you do for being slow.

    ----------------
    Barry Milton

  16. #16
    JST's Avatar
    JST
    JST is offline Diamond
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    Barry, take a look..... It isn't a few, its dozens, based on the area we can see. I can count at least 10, any one of which would keep it from seating..... and that is in about 1/8 of the surface area.

    Didn't come from using it as a drill...... or even falling on the floor.....

  17. #17
    BadDog is offline Stainless
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    Why use a drill instead of an end mill? Among the other points made, what about size? Most end mills are stocked in various increments, increments that are generally MUCH wider than typically stocked drills.

  18. #18
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    Barry, take a look.....
    I did :rolleyes:

    If you've never worked in a production shop, this looks awful. If you've drilled a zillion holes with a drill press the size of Texas, it looks typical. Not uncommon in a multiple operator shop.

    ---------------
    Barry Milton

  19. #19
    JST's Avatar
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    Ok, whatevah

  20. #20
    northernsinger is offline Titanium
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    You guys are funny: I'm going down to look at the bit again. There's something to what each of you say of course.

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