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  • Drilling "long" holes on lathe

    OK, somewhat of a simple question I think ....

    I'm trying to drill a 1/8" hole thru a 2" long 1/2" dia basic steel (1020 ?) rod using a lathe. Rod held in a collet, drill in tailstock chuck.

    1st try) I center drill and then 1/8" drill, using around 1500 RPM. (using cutting speed of 100, => rpm > 2000). By the time the drill gets out the other side, the hole is very noticeably off-center. Used cutting oil & I pecked the drill a number of times to clean out the chips.

    2nd try) same as above, but only drilled 1/2 way ~ 1", then flipped part around and did the same from the other side. So both holes started out concentric and met in the middle, though don't know how straight the resulting hole is.

    Now trying the same with aluminum rod, but using #32 drill (slightly under 1/8). Centered drilled, drilled 1/2 way, flipped part, centered drill and drill rest of way. Drill bit went farther than 1/2 way this time before seemingly broke thru into hole from other side. Going in with 1/8" reamer - should have been a nice simple ream, but reamer had lots of problems getting thru, I think due to hold not being straight.

    I'm guessing the drill bit is wandering off-center as it's going thru the part ? Is there a better way to drill this hole. Gotta be a way to get a straight clean hold thru 2" ?? I'm trying to keep the drill length a bit shorter so there less chance for the drill to bend. Peck it more ? Runout on the chuck ? Maybe do it on a mill instead ?

    The hole straightness isn't that crucial (steam passage into cylinder), but want to know for future endeavors.

    Suggestion ?

    Thanks,
    Mike

  • #2
    I think you should use a gun drill to drill deep holes - almost a reamer in that the main body of the drill will keep the hole straight.
    Other way is to bore the hole but never tried at 1/8" as I've never seen a boring tool that small.

    Peter
    I have tools I don't know how to use!!

    Comment


    • #3
      Originally posted by mlucek

      The hole straightness isn't that crucial (steam passage into cylinder), but want to know for future endeavors.
      Just curious.......if it's a steam passage........why run a reamer through?? I doubt that a little "offcenter" for a steam passage would cause any problems.

      Also.....for holes that I wanted "straight" and didn't have a gun drill (and was sure I'd have "some" wander)...........I just used a larger diameter bar, drilled straight through and then mounted it between centers and turned the OD down to my final diameter.........faced the ends and had a finished piece........Might be some "stress related" issues (depending on what the final part was for), but it worked for me..........

      BTW............If your drill is sharpened "correctly", you should experience "minimal wander". Not as good as a gun drill, but should work.......


      Regards..........Rodg
      RPease

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      • #4
        On parts having deep holes that have to be located to a feature, it's usually simplest to drill the hole and then machine the feature using the drilled hole for a location reference. You get a better shot at concentricity in a lathe if you drill undersize a bit then bore to drill size three or four diameters deep. This gives the drill good initial guidance.

        I know it's tough to bore 1/8" ID in a lathe but maybe you could bore it with an endmill.

        Comment


        • #5
          I have success with this kind of operation by using a "guhring parabolic drill" which I purchased from MSC.
          ralphe

          Comment


          • #6
            Originally posted by RPease
            Just curious.......if it's a steam passage........why run a reamer through?? I doubt that a little "offcenter" for a steam passage would cause any problems.
            You're correct, I don't need the reamer or much concentricity. I was merely using the drilling/reaming as machining practice in my class. Can't learn unless you try something .

            Was quite surprised at how far off-center the exit hole was in the steel rod I was using. Definitely visible to my eyes. I tried a 2nd rod with the same result. The 3rd rod I drilled from both ends and met in the middle with satisfactory results. Again the concentricity wasn't that important.

            Also.....for holes that I wanted "straight" and didn't have a gun drill (and was sure I'd have "some" wander)...........I just used a larger diameter bar, drilled straight through and then mounted it between centers and turned the OD down to my final diameter.........faced the ends and had a finished piece........Might be some "stress related" issues (depending on what the final part was for), but it worked for me..........
            Hmm, didn't think of doing it that way, but makes sense !
            I know it's tough to bore 1/8" ID in a lathe but maybe you could bore it with an endmill.
            Don't think I've seen a 1/8" e.m. with a 2+" long flute area. Cutter deflection would snap that e.m. pretty quickly

            Mike

            Comment


            • #7
              It ain't easy. You'll get some drill wander the best you can do. Maybe the first thing to explore is how symmetrically sharpened is your drill bit. Even a slight variation between the cutting lips can add up on a deep hole. A more expensive drill bit might be more symmetric...maybe.

              You're on the right track to drill halfway, I think, to reduce the total error.
              ----------
              Try to make a living, not a killing. -- Utah Phillips
              Don't believe everything you know. -- Bumper sticker
              Everybody is ignorant, only on different subjects. -- Will Rogers
              There are lots of people who mistake their imagination for their memory. - Josh Billings
              Law of Logical Argument - Anything is possible if you don't know what you are talking about.
              Don't own anything you have to feed or paint. - Hood River Blackie

              Comment


              • #8
                Use a new drill

                I would use a brand new drill. If the flukes on the drill are not the same length it can cause problems. If one fluke is just a little bit shorter than the other it Will wander. Then watch your feed pressure and withdraw frequently to clear chips. This is the way I've had success with.

                Comment


                • #9
                  If you don't mind taking the time you may be able to drill the hole through and be much closer to center than you indicated.

                  You'll need to make a 1/8" D bit long enough for the depth needed. Best made from 1/8" drill rod; harden the cutting section. Also from 1/8" drill rod, turn a cone and harden; use this as a punch to make a new starting point in the bottom of the hole (see below).

                  Start the hole with a 1/8" diameter center drill. Drill to a depth of 1/4" or slightly more with a #33 or so, i.e. remove all of the leading hole from the center drill. Best is to then use a tiny boring bar to carefully bore the first 1/4" to 1/8" but a 1/8" reamer should be adequate. This first section guides the remainder so the more accurately done the better.

                  Ream using the D bit and lots of oil, clearing chips frequently - a D bit doesn't have much room for swarf. Ream until the bottom of the hole is flat, i.e. remove the cone depression left by the #33 drill. Use the punch tool to make a new (centered) starting point in the now flat area in the hole; this ensures the #33 doesn't follow any drift from the last pass. Deepen the hole by 1/4" using the #33 drill; proceed gently so the bit isn't forced off center. Don't go more than 2 diameters since this drill can drift slightly off center. Repeat these steps until reaching the desired depth.

                  Both the D bit and the punch are guided by the existing part of the hole so by flattening the bottom of the hole and restarting after each 2 diameter section the accumulation of drift is minimized. The #33 drill removes the bulk of the material to reduce the number to times the D bit must be cleared of chips.

                  Admittedly not fast but it seems to reduce drift considerably (I've only done this once).

                  John
                  Location: Newtown, CT USA

                  Comment


                  • #10
                    http://www.wisc-online.com/objects/MTL8602/MLT8602.htm
                    tHIS WILL ANSWER YOUR QUESTIONS

                    http://wttool.mywowbb.com/
                    this is where I got it from!

                    Comment


                    • #11
                      I drill a 1/8" hole thru 4, 5/8" hardened steel shafts 13 1/2" long almost every week. It is for a special Hydraulic cylinder I make. I had the same problem as you until I spent some quality time making sure my tail stock and head stock were true. Now I can drill from each end and meet in the middle with very little missalignment. I found also that a well centered start and a 1" pilot hole also helped guide the longer drill bit. The biggest issue is patients, clear chips often, like every .1" once the flutes are unalble to self clear (Deeper then an inch) and feed as slow as possible. I hand feed cause I can tell by feel when I need to clear chips. I don't start he job if I don't have an hour to do each shaft.

                      Hope this helps

                      Wayne
                      Last edited by zukIzzy; 11-29-2007, 10:59 AM.

                      Comment


                      • #12
                        Do like Zuk....

                        I have drilled 9" deep at 3/16" diameter and come out 0.01 off at the far end.

                        I KNOW my tailstock is tipped down a bit, so that didn't do any harm.

                        1) drill should have a very short fluted area, the rest blank shank at full diameter

                        2) peck drill no more than 1/16" at 3/16" diameter.

                        3) clear chips every "peck".

                        4) do not force the drill

                        5) start on-center

                        6" oil won't hurt.
                        1601

                        Keep eye on ball.
                        Hashim Khan

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