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  • Help me go go in the right direction ...

    Wanted to drill a 3/16 hole through some aluminum 6061 bar - 2" by 2" ... I set it up in the Kurt vice on my trammed in mill, and then spot drilled a starting point with a center drill, and then drilled through the block with the 3/16 drill. I used the proper speed according to the chart on my wall.

    The entry hole is where it should be, +/- 0.003". But the exit hole is about 0.050" off !!!

    Wha happened?

  • #2
    If I understand right, the hole was thru 2" thick? Sounds like you started out OK, did you peck drill? I would for sure. Maybe used a stub drill instead. Figure the shorter the length of the bit sticking out the more likely your hole will come out straighter.

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    • #3
      I use cutting fluid on a hole that deep. Helps the chip travel up the drill flutes. Choking the flutes will make the drill wander. Also I've found that if I've sharpened the drill with unequal length lips, I have troubles.
      I cut it off twice; it's still too short
      Oregon, USA

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      • #4
        This might be better accomplished on a lathe, and perhaps drilled halfway from each end with a 1/8" drill. Then look at the hole to see how well it lines up, Finally, perhaps, use an expanding reamer in steps to achieve optimum alignment. If the bore is not critical, you could just follow up with the 3/16" drill, which should come out concentric on both ends, and call it good. A lot depends on the actual requirements.
        http://pauleschoen.com/pix/PM08_P76_P54.png
        Paul , P S Technology, Inc. and MrTibbs
        USA Maryland 21030

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        • #5
          Sounds like maybe the drill's grind isn't so great. At almost 11x's the diameter in depth, even a small error in angle or straightness will have the bit drifting off center. I'll start a hole like that with a screw machine length drill and run the first inch or so with it, then switch over to a standard jobber length drill to finish. That jobber drill though, needs to be right. Namely straight (lot's of drills, even name brands aren't) and the point needs to be sharp of course, but also accurately ground.

          It's also possible you had some flute packing going on, that will make a drill wander also.

          I just need one more tool,just one!

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          • #6
            Originally posted by PStechPaul View Post
            This might be better accomplished on a lathe, and perhaps drilled halfway from each end with a 1/8" drill. Then look at the hole to see how well it lines up, Finally, perhaps, use an expanding reamer in steps to achieve optimum alignment. If the bore is not critical, you could just follow up with the 3/16" drill, which should come out concentric on both ends, and call it good. A lot depends on the actual requirements.
            Using the same bit, why would the lathe produce a result any different then the mill?

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            • #7
              Originally posted by reggie_obe View Post

              Using the same bit, why would the lathe produce a result any different then the mill?
              The use of a drill in the lathe DOES seem to make the hole straighter. Seems to average out the errors to go straight.

              I could propose reasons, but they might easily be wrong, and would provoke more controversy. Be satisfied with the fact that it does.
              1601

              Keep eye on ball.
              Hashim Khan

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              • #8
                Thanks for the responses (so far, keep em coming).

                I did peck drill, but maybe not enough pecking. It was late in the evening and this was "the last hole" before the part was finished. So, I probably let the flutes fill up too much.

                No lubricant. I sometimes use kerosene on aluminum - is that a good choice?

                In this case the requirements are just that the entry point of the hole be in the right place. The exit being off by 0.050" is 'okay', but I want to avoid that in the future.

                And... well... the drill was one of Horrible Fright's finest... so the grind could easily be off.

                Comment


                • #9
                  Originally posted by Dan_the_Chemist View Post
                  Thanks for the responses (so far, keep em coming).

                  I did peck drill, but maybe not enough pecking. It was late in the evening and this was "the last hole" before the part was finished. So, I probably let the flutes fill up too much.

                  No lubricant. I sometimes use kerosene on aluminum - is that a good choice?

                  In this case the requirements are just that the entry point of the hole be in the right place. The exit being off by 0.050" is 'okay', but I want to avoid that in the future.

                  And... well... the drill was one of Horrible Fright's finest... so the grind could easily be off.
                  Friends don't let friends use HF drills

                  Kerosene is good, so is WD-40 (it's one of the few things WD is actually good for). Aluminum can be tricky, it conducts heat very well, it also loses it's temper at a fairly low temp. In a deep hole, without lubrication even good Aluminum can turn sticky quick.
                  I just need one more tool,just one!

                  Comment


                  • #10
                    You can easily drill a hole with the lathe and it will be off as well. It's easier to see with the lathe if the start of the hole is concentric, and you tend to make a correction before committing to drilling the full hole. Even then, if there's a momentary buildup of debris on one cutting lip, it can sent the bit off to one side, and then the hole might follow that. Once there's even a slight deviation from center the drill bit will flex enough to go there nicely.
                    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                    • #11
                      In the lathe, you do better with an "aircraft" type drill, one with short flutes and a longer solid round shank. Tends to follow the straight path better.

                      1601

                      Keep eye on ball.
                      Hashim Khan

                      Comment


                      • #12
                        Vice was trammed, did you clock the piece ?
                        clamp a DTI to spindle , check 2 faces on the work .

                        Comment


                        • #13
                          Originally posted by wierdscience View Post
                          I'll start a hole like that with a screw machine length drill and run the first inch or so with it, then switch over to a standard jobber length drill to finish. That jobber drill though, needs to be right. Namely straight (lot's of drills, even name brands aren't) and the point needs to be sharp of course, but also accurately ground.

                          It's also possible you had some flute packing going on, that will make a drill wander also.
                          Umm, I dont know. He prolly knows how to punch holes in Metals. Go with his plan. I mean he is Weird right, dont poke it JR

                          My old yahoo group. Bridgeport Mill Group

                          https://groups.yahoo.com/neo/groups/...port_mill/info

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                          • #14
                            As stated above, check to see if you have a good quality drill, in good condition (no hardware/bigbox store chinese specials) and of course the head in tram (and that your quill travels perpendicular to the table). I use good quality new-ish bits for critical holes.

                            I'll often start such holes ( deep, requiring "accurate" location on both sides), using a shorter (stiffer) drill, drill to the capacity of the short drill, which gets the longer, less rigid, drill "aimed" in the proper direction, and reduces the required drill-depth of that more flexible drill. Also, the chips need to be cleared VERY often (I keep toothbrushes around, with the bristles cut down to make the bristles stiffer, to swipe chips off the bits). .

                            On a bridgeport, I've drilled thru a 12mm dia hole in a 12" block of aluminum (from both ends) with the holes meeting in the center with no visible offset with this method. Used a couple of different shorter lengths, smaller diameter sizes, then a long 12mm drill, the block clamped to a rt-angle plate, hanging over the edge of the bridgeport, took the full quill travel plus some knee travel, with that final bit clamped in an ER collet holder, the center and vertical axis indicated from identical faces on each end of a carefully squared block (surprised myself that worked as well as it did, but was a real PITA, which I don't care to repeat).

                            Drilling isn't a particularly precision operation, with regard to diameter, form or position, good bits are key. (oops, just saw your post regarding the Horrible Freight bits--that's probably the primary problem, mystery-metal, mystery-grind, mystery accuracy). Don't even think about using those if you really need to drill a straight hole, or a round hole, or an accurate diameter hole. Use some lubricant, kerosine is OK if you can stand the stink, WD 40 is ok (I keep it in small squeeze luer-lock bottles with a dispensing syringe for aluminum).
                            Last edited by clr2; 01-18-2020, 05:20 AM.

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                            • #15
                              Make a D bit. ClickSpring has a video showing how to make one.

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