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Thread: 3/8 304 stainless 470 holes,help

  1. #1
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    Jan 2008
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    st.croix valley,mn
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    Angry 3/8 304 stainless 470 holes,help

    bought some sgs 5/16 dream drills (carbide)for a job, specs say,something like 1400 rpm .004feed. i can only get about thirty holes or so and the the drill breaks down . i have been up and down the rpm and feed spectrum but just cant seem to find a happy medium.the drills are a 140deg so i didnt spot them, had the plates annealed at the heat treaters but that didn,t seem to change anything.any sugestions would appreciated.

  2. #2
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    Is this a mill or lathe application?
    How are you holding the drill, in a collet or.. ?
    How deep are the holes?
    Thru or blind hole?
    Any peck cycle?
    Food coolant or mister?

  3. #3
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    st.croix valley,mn
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    the part is 3/8 thick ,the holes are through,470 holes on each plate,using flood coolant,cnc mill.,the drill is being held in a er25cat 40 holder, ihave tried different peck depths, .187,.1,.05etc
    Last edited by mjm3xs; 01-08-2008 at 08:29 AM.

  4. #4
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    Atlanta Ga USA
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    Where does the drill failure begin?

    Is there any kind of deflection that you are aware of from feed pressure, that suddenly gets relieved as the drill exits the other side?

    Ag

  5. #5
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    no i dont think there is deflection the drill seems to chip out aprox 1/3 way up the cutting edge.

  6. #6
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    Feb 2005
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    Stainless is work hardening, try RPMs sloooow and feed high. This makes a chip thick enough that the heat is carried away with the chip.

  7. #7
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    no i dont think its deflection, iam clamped down to another plate, but after that first plate of holes,put the second plate on then there is holes in my subplate, and when the drill breaks through it is not cutting the bottom of the 304 out, more or less just stretches it.im almost thinking that the first initial peck is whats chipping the bit,the surface of the plates are not machined so the scale is still there,so i thought maybe i should use a spotting drill first?

  8. #8
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    Aug 2005
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    Atlanta Ga USA
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    Sintered Carbide is first and foremost shock sensitive.

    The traditional different grades are very close in hardness, the toughness is the major change.

    Micrograin is reputed to improve toughness, as well as sharpenability.

    If the failure always happens 1/3 way up the cutting edge, look for a reason to explain any form of shock there.

    What is the drill point geometry??
    Is there a traditional chisel center??
    or is the web rigged with a pressure relieving grind that gives the swarf a place to move without HUGE amounts of pressure and cold work?

    An idea to try - -
    Put another (clean&flat) plate below the work to see if the break-out or breakthru is fostering the shock.

    If the drill enters the second plate immediately instead of air the problem may go away.

    Hth Ag EDIT .....immediately (within a thou or three or four) instead of .....
    Last edited by agrip; 01-08-2008 at 11:25 AM.

  9. #9
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    talked to a rep he is sending out different drill,but now recomends 650rpm.009feed,no peck?3/8 thick no peck what do you think?

  10. #10
    Join Date
    Aug 2003
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    Default drill

    The big problem is when the drill is almost thru the work and the material stretches down into the old backup plate hole. During this time the material being drilled hardens , dulling the drill bit, even carbide. Keep the rpm down, feed up and plenty of coolant/lube.
    JRW

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