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How do you dead centre drilled holes? (Sieg X2)

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  • #31
    I was going to mention buttons but you beat me to it . Good job. I have a set in my box for real jobs that have to right.

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    • #32
      Another vote for the "prick punch".

      Mine are ones sharpened to a sharp point. maybe a 30 deg included angle.... spearpoint sharp. The ONLY thing they are used for is to lightly start a punch mark. They can 'find" the intersection of lines well.

      After using the prick punch, I deepen the punch with a regular blunter punch to leave something a drill can start in.

      Then, pilot hole drill. Either a spotting drill, or just a small drill that will start well in the punch marks You really only need enough depth to get the bigger drill started. But a real pilot needs to be deep enough that the following drill is drilling to max diameter before it runs out of pilot hole.

      If the location is less fussy, cut out some steps
      CNC machines only go through the motions

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      • #33
        I don't buy the 'bend a small pilot drill to self align with the prick mark' theory. Yes, your wee pilot drill will flex and dimple into the center of the punch mark, but you're following it up with a much larger, stiffer drill that isn't going to be as compliant. Simply having a divot doesn't actually help you mechanically locate the spindle over the hole - you're just hoping that your drill bends enough, and your hole will be straight enough.

        My own method depends on circumstance, but these days with sharp split point drills, I have no problem accurately starting holes in only a punch mark. All other comments so far about layout, picking up the lines, and punching apply. With a traditional helical drill relief, the process is punch-stub drill-pilot drill-final drill-ream. Any hole larger than 12mm gets a pilot hole regardless of drill geometry, about 25% of diameter. This clears the web on chisel point drills, and gives better cutting action on split point drills.

        My personal belief is that it is better to locate the hole on the point of the drill than the lips. I feel that even minor inconsistency in lip geometry can cause the drill to wander due to cutting forces, if the first part of the drill to engage the material is the lip, as the further towards the end of the lip the material engagement occurs, the greater the skewing force applied to the drill. By contrast, on a well ground drill the point is on the neutral axis of the drill, reducing the moment arm of any force applied. This is even better on a split point or 4-facet drill. Thus I feel the role of spotting, even if it creates a very small flat at the bottom of the dimple, is to create a guide for the drill, in the same way a center drill creates a guide for a center on a lathe.

        The spotting drill should have a tip angle slightly larger than the point angle of the drill (120° for 118°, 140° for 135°), so that the point of the drill is the first contact with the material. The spotting drill should be split point, so as to create a spot dimple with a sharp center point. If the drill wanders in the spot, the action of the sides of the spot in combination with the drilling force, should re-center the point of the drill back towards the center of the spot, like a crowned pulley centers a belt. If the drill is not aligned with the spot, the action of the sides should again guide the point to the center of the spot. By using this larger angle type of spot drill, the outside edges of the lips of the drill cannot engage the material until the point and inner edges of the lip have already engaged the material and began their cutting action, providing further security from wandering.

        Another thing is to consider your drills. On a small machine like the X2, air below the head is always at a premium. For that reason, I have been building up a collection of screw machine length, split point, parabolic flute drills from Maritool, specifically for use on my mills (CNC SX2, RF-45 clone). These drills are a lot stiffer than jobber drills, have a split point so locate accurately even with only a punch mark to start on, and more closely match the length of other mill tooling. 95% of the drilling I do on my mills is going to be less than 5 diameters deep - tapped holes for fasteners, dowel pin holes, clearance holes, bolt holes, etc. All a longer drill does is makes me move the head farther, extend the quill longer, and add more flex into the equation. Jobber drills are easy to find if you really need a longer drill, inexpensively, in good quality, even at the hardware store. Yes, quality drills like that from an industrial tooling supplier are more expensive - but the time and frustration saved makes it more than worthwhile.

        In specific regards to your X2, consider the following:
        - always lock down the X and Y axis motion before any drilling operation to prevent the possibility of the table skating.
        - since you're using the entire head as the downfeed mechanism, you need to ensure the Z-axis gibs are nice and tight, to prevent the head 'nodding' upwards from the reaction force from drilling - this can have a significant effect on drilling accuracy in these types of mill as it skews the entire spindle axis.
        - the factory 'Jacobs' style chucks given away with those machines are garbage, and often have belled jaws. They're a really good way to chowder up all your drill shanks, no matter how hard you tighten them. A quality drill chuck is worth every cent. A collet is also an acceptable way to hold smallish drills.

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        • #34
          Originally posted by Sun God View Post
          I don't buy the 'bend a small pilot drill to self align with the prick mark' theory. Yes, your wee pilot drill will flex and dimple into the center of the punch mark, but you're following it up with a much larger, stiffer drill that isn't going to be as compliant. Simply having a divot doesn't actually help you mechanically locate the spindle over the hole - you're just hoping that your drill bends enough, and your hole will be straight enough.
          ....
          .
          You just don't know the trick.

          Small drill, with a good point. Rough center it on the punch mark. Power OFF, lower it into the punch mark. Odds are it will shift, because it isn't centered. shift the work until it IS centered. Turn drill 90 deg, repeat. Move the work only in direction parallel to the drill edges. An x-y table is good for this.

          Now you don't depend on flex to center the drill. With a good split point (not the crap you get from a Drill Doctor) you can use a bigger drill, because it has a smaller tip.

          Not that critical? Rough centering may be OK. More critical? Use a center finder or wiggler.

          Always drill in far enough that the hole is still present and guiding when the drill starts cutting full diameter.

          Do not cram the drill into the work, that causes drifting. If it is that hard to get it to cut, go get a sharp drill.

          Don't drill too large a pilot. about the size of the web, or a bit larger is about right. the chisel point has to fit in the hole.

          Yes a spotting drill is better if you have one.

          Watch out for spotting drills that leave a big flat spot in the middle. The following drill may run around in there and get off-line.
          CNC machines only go through the motions

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          • #35
            Originally posted by Arcane View Post
            It sounds like you might have a runout problem from a bad chuck. Have you done any measurements to eliminate it as a contributing source to your problems?
            No, and I should. I have a spare chuck too, but I need a hydraulic press to separate the arbor.

            It only seems to be a problem with shanks up to around 6mm, or short tools like centre drills. My 8mm solid carbide end mill in the chuck cuts true (or much better anyway). I am guessing uneven jaw surface and play in the threads.
            Last edited by Swarfer; 10-27-2016, 07:54 PM.

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            • #36
              Originally posted by sewingmachine View Post
              I was going to mention buttons but you beat me to it . Good job. I have a set in my box for real jobs that have to right.
              I keep forgetting to comment on the buttons. They sound like something I will be needing a set of. The reason I keep forgetting is that I am looking at everything with a view to CNC'ing the mill in the not-to-distant future, and being unable to automate hole drilling (to a 'reasonable' tolerance) would suck. Of course, I will still need to do some procedures manually, but I want to be able to do as much as possible without any human input. Some slot drills are next up on my tooling shopping list. Not sure if they are any better at drilling holes though.

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              • #37
                Hi Sun God,

                Thanks for the tip on the parabolic "split point" (interesting nomenclature, considering the cutting edge vs. a regular drill) drill bits.

                I have the same opinion as you regarding the included angles and engaging at the tip, rather than the edge. Seems like straightforward mechanics, when one side engages, a moment of force will be generated about that point.

                - I always* lock my not-in-use axes
                - There is definitely a problem with my z-axis gib. I need to remove the head and fix it, but I don't have anything to hoist it on, and the pin that holds together a bone in my wrist, which works pretty damn well most of the time, can randomly cause a painful and violent spasm in my thumb, which isn't great when lifting machinery...
                - Yep, need a better chuck, though it is fine for carbide shanks. I still need to clean (and likely deburr) my collet set.


                *when I don't forget...

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                • #38
                  Hi J, can you clarify what you mean by the following line:
                  Don't drill too large a pilot. about the size of the web, or a bit larger is about right. the chisel point has to fit in the hole.
                  Doesn't the web cover nearly the entire radial range of the drill?

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                  • #39
                    Originally posted by Swarfer View Post
                    Hi J, can you clarify what you mean by the following line:
                    Doesn't the web cover nearly the entire radial range of the drill?
                    No, the thickness is what is meant. Essentially the chisel point should fit in the pilot hole so it starts on the cutting edges.
                    CNC machines only go through the motions

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                    • #40
                      Ah, cheers

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