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Thread: What type of drill bit to drill the sear?

  1. #1
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    What type of drill bit to drill the sear?

    Anyone know which type of drill bit I need to drill the sear? As it's hardened my guess is it need an engineers type bit but I don't know which one to get. Anyone know?

  2. #2
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    cobalt coated high speed steel would be my guess .

  3. #3
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    another one...hehe

    I would suggest using carbide bits, should have better results.

    Carbide drill bits cost more than steel or titanium coated drill bits, but will last longer and stay sharper if used properly.

    If you overheat a carbide drill bit, it will shorten it's lifespan fast.

    You could/should use a cutting lubricant to minimize that problem with dense materials like the sear is made to be.

    Always go easy and let the drill bit do the work, because applying too much pressure will quickly dull your drill bit.


  4. #4
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    it all depnds of the rpm of your machine if using carbide drills you want to run at least 5000 rpm with coolant or cutting oil.

    a standard hss drill should do the trick

  5. #5
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    Hi all, i can get cutting lube from work, I'll see if I can get a carbide drill from somewhere. I'll only be running at between 500 and 1100 rpm, I think the lower the rpm will yeild better results as It's less likely to overheat being that the sear is so hard! Although looking at some of the drill stats I may well be wrong!
    Last edited by longi; 02-26-2012 at 02:38 PM.

  6. #6
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    Maybe this will be more useful than just my words...

    Enjoy everyone.

    http://www.drill-service.co.uk/documents.asp

  7. #7
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    Yeah, I think I need to get someone to dril the sear for me, i've broken 3 drill bits and not done anything other than scratch the sear. Anyone in Blighty that can do it for me?

  8. #8
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    Use the proper rotational speed and feed rate for the metal and bit type you are using. Feed too slow or have a rotational speed that is too fast and you will burnish your finish and overheat your bits. Feed too fast for your rotational speed and your bit will cut too deep resulting in stress on the bit and other components.

    You really need to look up the proper feed rate for the diameter of your bit at a given rpm and bit material when used to cut a specified type of metal. There are charts for this information.
    Except for the Automag in front, its usually the man behind the equipment that counts.

  9. #9
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    Quote Originally Posted by longi
    Yeah, I think I need to get someone to dril the sear for me, i've broken 3 drill bits and not done anything other than scratch the sear. Anyone in Blighty that can do it for me?
    What what is the hole for?

  10. #10
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    Quote Originally Posted by luke
    What what is the hole for?

    Hi Luke, the hole is there to secure a sear extender i've made to the sear so I can mount the MPA-3 lower in the frame, so as to lower the operating pressure. I'll also be able tho move the MPA-3 further away from the sear in a cheapo attempt to dial out the short stroking in my Pneumag. It probably won't work but it's something to do!

  11. #11
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    if you just wanna extend the sear arm you could use a steel tube (or tubish thing:P) to go over the sear, n use set screws or crimp it to keep it on

  12. #12
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    Why not just weld on an extension piece?

  13. #13
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    Quote Originally Posted by luke
    Why not just weld on an extension piece?
    Nice idea but I don't have access to a welder!

  14. #14
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    Quote Originally Posted by BiNumber3
    if you just wanna extend the sear arm you could use a steel tube (or tubish thing:P) to go over the sear, n use set screws or crimp it to keep it on
    I'm thinking of making a sleeve now and bolting them together and adding some 2 part epoxy.

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