Announcement

Collapse
No announcement yet.

What Did I Do Wrong?

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

  • What Did I Do Wrong?

    I wanted to drill a 1/4" diameter hole through a 1.250" OD piece of brass, 3 1/2" long. I have a 6" long 1/4" drill which I used to drill the hole. I chucked the drill so about 4" of it was outside of the tail stock chuck. After drilling the centering hole, I started to drill the 1/4"hole through the brass. I used peck drilling and cleaned the chips from the drill flutes about every 1/4"to 1/2" (rather time consuming process). After I had the hole drilled through, it looked off center and when I measured it, the hole was 0.065" off center.

    I'm assuming it was drill wander which caused the off center exit hole. Am I correct? If it was drill wander, how does one drill a deep hole with out having the drill wander? If it wasn't drill wander, what caused the off center exit hole? Appreciate suggestions.
    Bill

    Being ROAD KILL on the Information Super Highway and Electronically Challenged really SUCKS!!

    Every problem can be solved through the proper application of explosives, duct tape, teflon, WD-40, or any combo of the aforementioned items.

  • #2
    Chips probably packed one flute,
    causing the off-center push.
    Could also be one cutting edge was sharper
    than the other or at not quite the same angle.
    It also helps to reduce the rake angle of the
    bit to zero (instead of positive) when drilling
    brass.
    -D
    Last edited by Doozer; 10-17-2014, 12:01 PM.
    DZER

    Comment


    • #3
      If you have the option, drill half way from opposite ends. will help a lot (it'll reduce the runout by more than half).
      ...lew...

      Comment


      • #4
        That is a long way to drill for a 1/4" drill bit and it is drill wander that does it. There are many thing that can cause it but basically drilling that deep requires a different type of drill. You can try starting with a short stubby drill to get a good stating hole then a standard length drill and finish with a long drill to minimize drift but there will still be some wandering.
        The shortest distance between two points is a circle of infinite diameter.

        Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

        Comment


        • #5
          Originally posted by loose nut View Post
          That is a long way to drill for a 1/4" drill bit and it is drill wander that does it. There are many thing that can cause it but basically drilling that deep requires a different type of drill. You can try starting with a short stubby drill to get a good stating hole then a standard length drill and finish with a long drill to minimize drift but there will still be some wandering.
          Work your way up in sizes too. Don't try to push the 1/4" drill through with out piloting first.
          I've drilled the full length of a jobber drill on my lathe before and ended being off less than .001 at the exiting end. It can be done.
          All of the above mentioned are points to take into consideration.

          JL.............

          Comment


          • #6
            Check out "gun drills". As others have said, that is asking a lot of any twist drill and if it was a cheapo Enco drill then there is a very good chance that the tip wasn't sharpened 100% symmetric, which means it will drift much worse than a high quality bit. I have a complete set 1/8" through 1/2" by 64ths of those extra long twist drills from Enco. They were on clearance for next to nothing and their quality reflects the price! They are handy for crude tasks, but not deep hole drilling in a lathe.

            Comment


            • #7
              Make your life easier.

              Originally posted by Fasttrack View Post
              Check out "gun drills". As others have said, that is asking a lot of any twist drill and if it was a cheapo Enco drill then there is a very good chance that the tip wasn't sharpened 100% symmetric, which means it will drift much worse than a high quality bit. I have a complete set 1/8" through 1/2" by 64ths of those extra long twist drills from Enco. They were on clearance for next to nothing and their quality reflects the price! They are handy for crude tasks, but not deep hole drilling in a lathe.
              I sometimes work with a very capable older machinist. His solution for these sorts of problems is simple---- he drills the hole he needs in oversize stock then mounts the hole between centres and turns the stock to suit. This solution may not work for everyone, in every case, but it is well worth considering at times. It has saved me some worry at times. Regards David Powell.

              Comment


              • #8
                You still end up with a curved hole most of the time unless you straighten the piece after it has been drilled.

                Gun drills are the right way to go but buying one for a one of simple job is pretty much out of the question for most of us.
                The shortest distance between two points is a circle of infinite diameter.

                Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

                Comment


                • #9
                  Feed and RPM are important too. Also how you drill the starting hole.

                  Too much feed/low rpm and you push too hard and force the drill off center as it plows instead of cuts.

                  With the starting hole using a center drill (Technically wrong but we all do it), I like to stop several times while drilling it and lock the tailstock ram for a second or two, then resume. This turns the center drill into a little boring bar (Do it before the tapered section is fully inside the work) and bores the hole on center by single tooth cutting action if the cutter is slightly off center or the hole has runout. Won't work with a drill since they have to sharp a tip angle and are too flexible.
                  Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

                  Comment


                  • #10
                    Have you checked the alignment of a center held in the drill chuck, versus the lathe center? Any time I've been careful about spotting the center first and clearing the chips as I go, but still ended up with an off-center hole on the other side, it has been due to poor alignment of the drill. It's much less of a problem for me now that I have a couple of better quality drill chucks, and a lathe with better tailstock alignment.
                    Max
                    http://joyofprecision.com/

                    Comment


                    • #11
                      The drill should always follow center if it is sharp and you don't crowd the drill.
                      Your approach to center should be slow untill the center of the drill reaches the solid bar.
                      The "rule of thumb" is; first pass no more than three times the drill diameter, second pass two times the drill diameter, all subsequent passes should be no more than the diameter of the drill.
                      One of these conditions wasn't met.

                      Comment


                      • #12
                        Originally posted by David Powell View Post
                        I sometimes work with a very capable older machinist. His solution for these sorts of problems is simple---- he drills the hole he needs in oversize stock then mounts the hole between centres and turns the stock to suit. This solution may not work for everyone, in every case, but it is well worth considering at times. It has saved me some worry at times. Regards David Powell.
                        That's a good way of overcoming the problem providing you have the excess on the OD and the part can be rotated.

                        JL.............

                        Comment


                        • #13
                          Any asymmetry in the cutting surfaces of the drill can cause it to wander off center. Once off center the outer edge of the drill face sweeps a greater area than the inner edge hence removing more material. The tip of the drill moves farther from center and describes a circle centered away from the desired bore. It will never return to center. The drill can handle a limited amount of curve but can certainly break from the constant flexing along its axis. Spring in the drill will also cause the hole to taper along its length as the sides of the drill wear into the curved hole.

                          Comment


                          • #14
                            Instead of a jobber drill use a screw machine drill. First drill a small dimple with a spotter drill. New, sharp drill is important. Make sure the tail stock is on center.

                            You could also try a 1/4" endmill in the tail stock.
                            Gary


                            Appearance is Everything...

                            Comment


                            • #15
                              Originally posted by JoeLee View Post
                              Work your way up in sizes too. Don't try to push the 1/4" drill through with out piloting first.
                              I've drilled the full length of a jobber drill on my lathe before and ended being off less than .001 at the exiting end. It can be done.
                              All of the above mentioned are points to take into consideration.

                              JL.............
                              Interesting...
                              With a larger drill, it is stiffer, so I would think it would drill straighter,
                              but also it has more web and larger center of the cutting end that pushes
                              more than it cuts (hence the reason for splitting the point and thinning
                              the web). With a smaller drill, it is less stiff, but has less to push through.
                              So I dunno which I would say is better. Will have to think a bit on that one.
                              -Doozer
                              DZER

                              Comment

                              Working...
                              X