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Making stubby drill bits

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  • Thrud
    replied
    Paul Alciatore:
    I buy Gaar Carbide endmills & burrs and they have started doing drills and reamers. Comparing their price with Travers or KBC they start to look cheap. Just a thought.

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  • Paul Alciatore
    replied
    Rotate,
    I am looking to buy one or more sets of screw machine bits for the very reasons mentioned here: stiffer and more clearance. If you have found a good price on these sets, would you please share the source?

    I suspect the higher cost is because they aren't sold in the higher quantities that Jobber bits are: they can be found in Drug Stores for Pete's sake. Also Screw Machine bits seem to be more frequently sold in individual sizes instead of sets. I suspect a manufacturer would buy a dozen or a hundred of the single size needed for a particular part instead of a single set. Prices are surely better in quantity.

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  • Thrud
    replied
    I read about some bone head drill company coming to the realization that a uniform web thickness would be a good thing to eliminate web thinning when regrinding the 5 billion times a shop would like to for reducing drill expenditures. Well, Duh! I mean, Doh!

    Albert
    Parabolic flute drills are used to more effectively remove the swarf. You should also note that colbalt drills have a thicker web than HSS and are a poor choice for work hardening materials such as Stainless Steel.

    It is a shame to drill SS, it is soooo shiney!

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  • Peter S
    replied
    Rotate,
    Why not just buy some standard stub drill bits? They are just short versions of normal jobber drills, and are cheap.
    I wouldn't be bothered shortening jobber drills, the web will be too thick.
    I have bought stub drills just for the sizes where they are most useful, eg. tapping drills, bolt clearance holes etc. No need to get a whole set.

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  • Rotate
    Guest replied
    Uncle Dunc,

    I've sourced reasonably priced screw machine bit. Needed to compare apples to apples. Thanks.

    Ablert

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  • Uncle Dunc
    replied
    >> Why are they so expensive?

    One drill is always going to be more than the per piece price on a set, but probably what happened to you is that the one you bought is a better grade of drill than the set you were comparing them with.

    Call MSC at (800)645-7270 and ask for a free catalog, or go www.mscdirect.com and search for 'screw machine'.

    >> What are they used for?

    One use is the exact situation you have, where a normal length drill won't fit in the space available. The other, as Stepside noted, is that they are stiffer, which sometimes means that you can omit using a pilot drill or center drill to start a hole.

    >> Why are they called "screw machine bits"?

    There is (or was, CNC may have displaced them) a class of turret lathes called automatic screw machines. If using the shorter, stiffer drill meant eliminating the pilot drill, that would save one position on the tool turret, which might eliminate a second machine setup, which would be economically significant if you're making a bazillion pieces.

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  • Rotate
    Guest replied
    I checked out the screw machine bits and they sure are expensive. For the price of a 1/2" bit, I can buy a whole set of the regular bits. As usual, I have follow up questions.

    a) Why are they so expensive?
    b) What are they used for?
    c) Why are they called "screw machine bits"?

    Thanks.

    Albert

    P.S. I asked these questions to KBC salesman, and I got the usual "I only sell this stuff" line.

    Leave a comment:


  • lynnl
    replied
    But it would seem to me that by the time the web'ed portion gets down into the hole, the lips have already converted that metal that used to live in that hole (ahead of the web) into chips.

    Tho I can see that as the web gets progressively thicker, back near where the fluting ends, the clearance space for chip ejection will be diminished. ... Okay, I guess I can kinda understand it.
    Thanks for the additional explanation.

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  • halfnut
    replied
    Mite is right, it rhymes, had to repeat that once again.

    The web of a drill bit gets thicker towards the shank, as a drill is shortened by cutting off or repeated sharpenings this needs to be thinned or the web split.

    I was perusing through a catalog the other day and noticed some drill bits that were advertized as having an equal thickness web the lenth of the flutes. This is an exception and not the norm.

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  • metal mite
    replied
    Lynnl,

    Most of the feed pressure in drilling is created in the web.
    The lips cut freely because of the positive rake.
    The web is for all practical purposes, wearing the metal off.

    The web area will work harden stainless steels while drilling.
    Split points, or a special " S " grinds are frequently used on stainless.

    You run a lead drill thru so you don't have to force a large drill's web thru the metal.

    mite

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  • lynnl
    replied
    Question: (..regarding Halfnut's comment about thinning the web). Why is that necessary? I'm not taking issue with it. I've seen that mentioned before, but I've never really understood the purpose it serves.

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  • Thrud
    replied
    Albert

    Mite is right, spotting drills or stubbys. If you have a collet holder non-taper length drills can be gripped by the collet but you won't gain much unless you have a NT40 or NT50 shank tool holder (more empty space behind the collet).

    Leave a comment:


  • Peter Sanders
    replied
    Hi Albert

    <font face="Verdana, Arial" size="2">Originally posted by Rotate:
    I had to drill a 1/2" hole on a part that tall enough that my standard 1/2" drill bit was too long. Over the years I collected motly collection of bits, and I decide to sacrifice one of the bits by shortening the shank. To get the clearance, I had to grind off almost the entire length of the shank. To my horror, the drill chuck couldn't grab the fluted portion of the drill. After looking at the flute and the drill chuck, it became obvious why. The drill chuck has three jaws and the drill only has 2 landing area. Lesson learned.

    Now how do you properly shorten a drill bit?

    Albert
    </font>
    I don't propose this as the "proper" way to shorten a drill bit, however I am sure that if you were willing to sacrifice a drill bit you could use an angle grinder to cut off most of the drill bit (without overheating of course) and then sharpen the remainder. As it was pointed out though, don't forget, the web will be thicker and you may need to relieve some of this to retain a good cutting edge.



    ------------------
    Kind regards

    Peter

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  • halfnut
    replied
    Mite is right, cut down working end, shank is soft to allow the chuck to bite. Could buy one of those new Albreight chucks with the diamond coated jaws. But that won't work if you are past nice round part.

    Just cut off the cutting end, regrind it. Remember that the web will be thicker now, it will have to be thinned or split. Easy if you have a drill grinder that does this, not hard to do with a grinder freehand if you have a sharp cornered wheel.

    [This message has been edited by halfnut (edited 05-19-2002).]

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  • Stepside
    replied
    The Mite is Right. Get a screw machine bit. In fact save your coins and buy a whole set---98% of the time you will wonder why they even bother to make the jobber length bits. I find for most work they eliminate the need for a starter bit. Now for .250 and larger holes in sheet goods get a set of annular cutters if you want round holes.

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