Announcement

Collapse
No announcement yet.

Drilling help needed

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Drilling help needed

    Hey guys, I need a little drilling advice. I'm making some brake linkage clevis pins for a friend for his Harley. Seems like a simple enough project. Turn 1" stock to .743 to a shoulder, cut off part, face cut off end, chamfer all corners and then drill through small end to accept a cotter pin. Easy as pie right. The problem I'm having is the cotter pin hole. I need to make a 7/64 through this .743 part made of 304 stainless. My old BP owner's manual says for stainless I should be running over 50 fpm, which means crank the old step pulley machine as fast as it'll go (2750 RPM)for a bit this small correct?
    I have been center drilling to get the hole started then switching to a normal drill bit and so far my results are three scrapped parts and three broken drills, two HSS and one cobalt. I have been drilling dry. One was just about to break through when the drill broke, the other two only made it part way through.

    Any advice?

    John


    ------------------
    Pursue Excellence and the rest will follow.
    Pursue Excellence and the rest will follow.

  • #2
    John,

    I would use some lubricant. Being SS you have to keep up the feed pressure and don't slack off for a moment. When drilling 4130 wing spars we used wax lubricant. You plunge the drill in the wax stick before drilling and it melts down and lubes the cut as the drill heats.

    I would also slow it down some, maybe 1000 rpm with agressive feed.

    [This message has been edited by Evan (edited 05-31-2004).]
    Free software for calculating bolt circles and similar: Click Here

    Comment


    • #3
      Evan, you're right on the money. 1115 RPM and some tap-o-matic cutting oil and everything seems to work fine now. Thanks for the replies guys.

      John

      ------------------
      Pursue Excellence and the rest will follow.
      Pursue Excellence and the rest will follow.

      Comment


      • #4
        I agree with Evan, slow down to about 1000 RPM and you have to use coolant of some sort. Preferably something made for high heat or for stainless usually a sulpher based oil. Don't let the drill get too hot or most oils get thin and move away from the piece. A cobalt drill is better as it will take more heat than a plain HSS but only to a certain point and the web is thicker so it provides more support for heavier feeds. They are usually a 135 degree split point which means the lip has more support also and it is self centering and cuts through the steel easier. The problem with most CRES (including 304) is it tends to work harden as it is being cut. To avoid this a heavier feed is employed so you are constantly cutting into fresh metal instead of the thin layer that you just cut through that has been work hardened. Another example is I never use a taper tap for tapping CRES, I always use a plug tap to a larger, heavier cut is taken and I am not trying to make a smaller cut with the taper tap into work hardened material. It's like cutting the scale off of hot rolled steel. The scale is hard and abrasive on cutters, that’s why you always make your first cut below the scale to minimize the contact the cutter has with the scale. Imagine if every cut on CRES leaves a layer of scale after every pass. You have to take a heavy cut every time or you will be cutting through that scale every time, very hard on the drill, it gets dull fast. Start off drilling slowly taking a heavy cut with good healthy sized chips, increasing the pressure if the chips are not a good thickness. When you are getting close to drilling through back off on the pressure a little bit as the drill will tend to push through getting stuck in the flutes and sucking the drill through or snapping the drill off as you have found. Good luck and have fun.

        Mike


        [This message has been edited by coles-webb (edited 05-31-2004).]

        Comment

        Working...
        X