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Is this normal?

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  • Is this normal?

    Watch this video:

    Right around the one minute mark, the center drill contacts the workpiece and if you look closely, it wiggles around a bit after it apparently bites in.

    Is that normal? My lathe does this all the time and it annoys the hell out of me. My tailstock is locked down tight, I have good drag on the ram clamp but even when I am step drilling, the tip of the drill wiggles a bit. I appear to be getting okay holes, but it just doesn't look right to me. I've re-centered my tailstock four or five times with no difference.
    Dial indicators all over the ram say it's a bit high vertically (.0015), but dead on horizontally. It's almost as if the ram is coming out at an angle. Or am I foolishly thinking being off .0015 vertically isn't enough to be causing the wiggles?

    What can I do to prevent (or eliminate) this?

  • #2
    Use a ball endmill

    edit;- Odd that its high, wear should make it low. Has it been shimed to high ??

    Last edited by jugs; 04-17-2011, 02:00 AM.

    I used to be indecisive. Now I'm not so sure , but I'm not a complete idiot - some bits are still missing


    • #3
      It looked to me like the round bar had a small tit in the center which forced the bit off-center as it was advanced into the bar.

      The cutting tool used to machine the end of the bar wasn't at the correct height. Correct that, and the bit wouldn't drift.
      Any products mentioned in my posts have been endorsed by their manufacturer.


      • #4
        The video shows a centre drill. It actually moves to the side a considerable amount as it bites and self-centres itself. I assume the tailstock in the video is not horizontally centred. If your problem is with step drilling then you are using relatively long twist drills, which are quite flexible. You can never guarantee that the drill is perfectly straight or mounted in the drill chuck perfectly parallel to the spindle axis, so it is not uncommon for the drill to appear to wobble. None uniform geometry of the cutting edges may exaggerate the effect.

        Just a thought or two.


        Ps: Mount a piece of ground rod in the drill chuck and run a dial indicator along it (horizontal and vertical).


        • #5
          When starting the centre drill bring it into contact with the work very lightly, just barely touching. Leave it there for a few seconds and then slightly increase the pressure very slowly until it begins to start drilling. Once it has begun to bite then the pressure can be ramped up to drill properly and it will be dead on centre, every time.
          Free software for calculating bolt circles and similar: Click Here


          • #6
            Originally posted by Evan
            When starting the centre drill bring it into contact with the work very lightly, just barely touching. Leave it there for a few seconds and then slightly increase the pressure very slowly until it begins to start drilling. Once it has begun to bite then the pressure can be ramped up to drill properly and it will be dead on centre, every time.
            Ditto on this one. Even a small tit won't matter if you do it this way and also this is the way to correct a centre hole if it is offset from the center a little bit.
            Amount of experience is in direct proportion to the value of broken equipment.


            • #7
              I look at my center drill less like a drill, and more like a form boring bit.

              Because if you lock your tailstock ram, the bit will be rigid enough to just use one flute to bore the hole. This insures a properly centered hole. Even if its a little oversized from your tailstock being too high/low/left/right. (Idealy you want the flutes of the bit aligned with the axis your 'out' or you might end up with rubbing)

              the way I drill is basicly as evan said, bring it slowly at first, once the tip is in a little to the first flat section, lock the tailstock ram, wait untill shavings stop appearing, then feed it in deeper, lock the tailstock ram one last time at final depth, Wait for shavings to stop, and done!
              Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.


              • #8
                The workpiece had been faced. If you face a piece like this preparatory to drilling, it's a good idea to swap in a cutter that can cut into the face a little more when you've finished facing, and tweak the cutter into the face in the centre to give a small crater to help the drill start in the right place.

                Also, if you watch through to see the operator use the chuck key to remove the centre drill, he applies pressure towards the headstock. That always risks the chuck and taper popping out of the tailstock and damaging lots of stuff. To tighten or loosen a drill in a tailstock always apply pressure across the bed, risking turning but not dropping out, or towards the tailstock.

                Added: Thinking about the whole presentation, you across the pond may not catch the typical "I'm pretty and I'm reading this from a card, but I know sweet FA about lathes or drills" voice of the narrator. Just like the report on that poor Yale student that said

                "A lathe is a machine used for shaping wood, metal or other material by way of a rotating drive that turns the material being worked on against cutting tools."

                I mean, yes, true, but if the reader didn't know what it was to beforehand with, they're not going to be any better off after reading that, are they ? The journo must have asked a prof, and the prof gave a logical answer.

                Better get the ignorant to tell the ignorant. If the informed get involved, brain overload !

                I like this Dilbert cartoon - the second in this link -
                Last edited by rohart; 04-17-2011, 05:41 AM.
                Richard - SW London, UK, EU.


                • #9
                  Unless you are needing a centre hole to support a centre then forget centre drills.
                  They have been superseded by better options but unfortunately the text books have not kept up.

                  Spotting drills do a far better job, not as prone to breakage and save an operation in that they are the first pilot drill.

                  Evan mentioned a valid point in that you allow the drill, any drill, to just touch and find it's own centre before proceeding.

                  Having the tailstock barrel clamp just nipped a bit also helps.

                  Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.


                  • #10
                    It's likely common for the tailstock to be off center or out of alignment one way or another. In addition to being high or low, forward or rearward, it can be tilted and or skewed. Put a center in the spindle and another in the tailstock. Wind the tailstock ram almost all the way in, then bring it up to the chuck and pinch a flat plate between the points. The plate will likely tilt because the points aren't aligned. Then back the tailstock away and crank the ram most of the way out. Slide the tailstock in and pinch the plate again, avoiding using the dimples that the first test made. Each time you repeat this type of test, make sure that each point contacts a fresh area on the plate.

                    The plate will likely have tilted differently this time. Once the ram is aligned with the spindle axis, you hope to find that the drill chuck will hold a bit on axis as well. Theoretically now, the drill bit should not wander when it contacts a workpiece which has been faced.
                    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                    • #11
                      I must say I love the way he tightened the tailstock in the earlier part of that video. Carpal Tunnel Syndrome he we come.

                      Not a good thing.



                      • #12
                        Originally posted by rohart
                        The workpiece had been faced.
                        Yup, just not very well, or I suspect that wobble would be significantly reduced. Either that, or as pointed out, reduce the initial pressure.
                        "I am, and ever will be, a white-socks, pocket-protector, nerdy engineer -- born under the second law of thermodynamics, steeped in the steam tables, in love with free-body diagrams, transformed by Laplace, and propelled by compressible flow."


                        • #13
                          This mught already have been said.
                          Always run a center drill first.
                          Turn or file away the teat.


                          • #14
                            I just hope those hands were not the hands of the female narrator!!!!


                            • #15
                              I think Darryl nailed it , but here are a few things you can do to address your problem
                              Do the Darryl tests, but you need to put a mark with a felt tip marker on the top of the drill chuck you use. If you have several chucks, or taper ADAPTERS, each should be marked. After you test the allignment, remove the chuck and rotate it it 90 degrees, so the mark is now towards you. Repeat this rotation again at 180 and 270 . Also do the test with the tailstock slide fully extended and fully (almost ) retracted. These 8 readings will show where the error is previlent.
                              Nothing is perfect in this world, so what you are doing is dialing in for accuracy.
                              If the 270 reading was the most concentric for example, You now PAINT a spot on the top of the drill chuck in that position, so the next time you use the chuck, you will insert it in the tailstock barrel (paint spot up)in its most optimum place. If you find ( as most do ) that the shorter tailstock is more accurate, try to start a hole with the shortest extension of the barrel.
                              The most common error you describe is in/out which is caused by tailstocks being adjustable for tapers and that is fixable . Lathes are made with a top/down error on the top side (.001" or .025mm) to compensate for wear and part weight. When you read low, only a tailslide rework can raise it back.

                              The other variable is the position of the flutes on your drill, or centerdrill.
                              Get in the habit of always setting the flute horizontal !
                              This makes the drill position less sensitive to top/down error, and offers the advantage of drilling without a centerdrill to start !
                              This is done by having the jobber drill right up to the work, and then moving your Lathe Toolbit about 1/4" behind the drills lips and barely touching the drill. The cutting tip of your toolbit will be in the flute relief area ( and therefore protected) due to the helix of the drill, and the heel of the toolbit will be touching the flute.
                              Now give the crosslide about a .002 feed IN while you contact the part by turning the tailstock handle, as you feed into the work, back out the toolbit with the left hand and you will have a perfectly started drill bit. If you have a bent drill, poorly sharpened drill or a bad chuck, you may need more than the .002"

                              No machine is perfect, but using your eyes and logic can narrow the error.


                              I agree with the earlier poster, that a ball endmill will give you the most accurate hole start
                              Green Bay, WI