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Thread: Micro drilling burr free

  1. #1
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    Default Micro drilling burr free

    This is my first time posting so please bear with me. I am working on a project that requires me to drill a through hole in 304 stainless steel. The hole is .011" and is .010" thick. My problem is that when I punch through there are one or two burrs left on the hole exit. I've been told to use a backer but both sides of the hole are located in a recess. I am using a Bridgeport vertical mill running at 4200 rpms and a sensitive drill feed chuck to do the drilling. I fill the recess with a synthetic/water mix coolant. If any one has an idea I would appreciate it. By the way I have a reamer for that size but I am having troubles with carbides. My sensitive feed 1/8" drill chuck has too much runout (.005") for the carbide snapping them instantly when you touch the material. My 1/16" drill chuck runs much truer but so far the only carbides I can find have an 1/8" shank. The drill bits that I am using are cobalt. Goes through the stainless like butter.

  2. #2
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    That's what drill bits do when you don't have a backer--They leave burrs. The last thin layer of material gets pushed out in front of the bit. It happens with big bits and little bits. Have you looked into EDM?

    I don't know how you would grind them but a flat faced bit might help.

  3. #3
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    Quote Originally Posted by taquero View Post
    I am working on a project that requires me to drill a through hole in 304 stainless steel. The hole is .011" and is .010" thick.

    My problem is that when I punch through there are one or two burrs left on the hole exit. I've been told to use a backer, but both sides of the hole are located in a recess.

    I am using a Bridgeport vertical mill running at 4200 rpms and a sensitive drill feed chuck to do the drilling. I fill the recess with a synthetic/water mix coolant. If any one has an idea I would appreciate it.
    Manual table feed ? DRO ? Would deburring as a second operation be feasible ?

    Cogsdill makes tools that debur both sides of a hole in a single pass.


    Cogsdill offer small diameters, but whether they go down to 0.011" is something for you to inquire about. I have a couple of their Burraway models. Small, but not as small as you need.
    "There's a place for us,
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    Quote Originally Posted by taquero View Post
    I am working on a project that requires me to drill a through hole in 304 stainless steel.

    The hole is .011" and is .010" thick.

    I am using a Bridgeport vertical mill running at 4200 rpms and a sensitive drill feed chuck to do the drilling.
    4,200 RPM for an 0.011" drill in 304 Stainless seems a touch slow.

    For uncoated drills in 300 Series SS, Cleveland advises 60 sf/m. For 0.011" tool dia, 60 sfm appears to call for almost 21,000 rpm.

    For TiAIN coated drills, Cleveland suggests 110 sf/m. I think that calls for a touch over 38,000 rpm.

    Perhaps more speed could give you a better finish. Some kind of auxiliary spindle mounted to the BP quill could be one way to achieve higher speeds.
    "There's a place for us,
    A special place for us.
    Perspiration and chaos and sulfurous air
    Wait for us
    Somewhere."

    (Apologies to Stephen Sondheim who wrote the lyrics and Leonard Bernstein who wrote the music to Somewhere from Westside Story.)

  5. #5
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    Yeah, I was going to mention speed but I was too lazy to look it up. When I drill jets and vacuum ports for carburetors, I use the Dremel cranked all the way up. That's about 30k rpm. But, I don't think that will help with a burr in SS.
    Last edited by CCWKen; 01-22-2018 at 07:09 PM.

  6. #6
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    304 Stainless is prone to work hardening when one dilly-dallies, isn't it ?
    "There's a place for us,
    A special place for us.
    Perspiration and chaos and sulfurous air
    Wait for us
    Somewhere."

    (Apologies to Stephen Sondheim who wrote the lyrics and Leonard Bernstein who wrote the music to Somewhere from Westside Story.)

  7. #7
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    A flat faced bit is called a center cutting milling cutter. The geometry is fairly standard, but making it, especially in a small, home shop, may be difficult. Actually you may want a slightly concave face on that cutter so that the outer edge breaks through first. Wood bits are made this way to reduce chipping, but they still need backing. I am afraid that backing is the key and I would be looking at some way to do that, even in this recess. There must be some way to get something in there.

    As for those bits that deburr on both sides of the hole, do they even make them in such small sizes? Perhaps you could make a deburring tool that would work. Tool steel about 0.008" in diameter, sharpen it to a Dee shape near the end, then bend it at about 45 degrees in the middle of that Dee shaped area, providing a 45 degree cutting edge. Insert it in the hole and spin it while applying pressure in the reverse direction. Stop it to remove. It would probably be best to deburr the outside first to make the insertion of this tool easier.



    Quote Originally Posted by CCWKen View Post
    That's what drill bits do when you don't have a backer--They leave burrs. The last thin layer of material gets pushed out in front of the bit. It happens with big bits and little bits. Have you looked into EDM?

    I don't know how you would grind them but a flat faced bit might help.
    Paul A.

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  8. #8
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    Quote Originally Posted by Paul Alciatore View Post
    ... I would be looking at some way to do that, even in this recess. There must be some way to get something in there.
    One way could be to use Cerrobend (one of several commercial variations of the low melting temperature alloy known as Wood's Metal).

    Cerrobend melts at just under 160F (70C). Pour it into place, drill the 0.011" hole, then place the part in a tank of hot water ( > 160F) to melt and reclaim the Cerrobend for future use.

    Yes ?

    If this concept seems feasible, do some research on the variations of low melt alloys available now. There are several just within the Cerro line besides Cerrobend: Cerrosafe, Cerrocast & ect ...
    "There's a place for us,
    A special place for us.
    Perspiration and chaos and sulfurous air
    Wait for us
    Somewhere."

    (Apologies to Stephen Sondheim who wrote the lyrics and Leonard Bernstein who wrote the music to Somewhere from Westside Story.)

  9. #9
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    Check with Harvey Tool. They may have a milling cutter that would work or other solution.
    Toolznthings

  10. #10

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    As previously mentioned 4200 rpm is not nearly enough, I have used .015 drills and I always used cutting oil Mobilmet or CoolTool. With out some type of back plate there is always a burr, for the work that I did these were removed with a polishing stone. Do you have to hold a location, if so how are you starting the drill?

    frankie

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