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Problem drilling holes on the centre line of items

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  • #16
    Had the drilling in place problem when I first started working with my mill. After a while I discovered that the column was tilted, so any time I changed the tool from a short spot drill to a long drill, the point of the tool was in other XY position.

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    • #17
      Originally posted by Forestgnome View Post
      I'm thinking most likely slop in the quill. When I want a real accurate hole, I scribe, prick punch, center punch, then run a flat file over the surface to knock down the metal displaced around the punched divot.
      I've seen and had prick punches slide off the scribe line when the point sinks into the steel.

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

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      • #18
        Spotting drills are stiff but try a split point drill. They stay true.

        If there is any play in the quill that can be an issue. Especially if the quill was LOCKED for using the edge finder and not slightly LOCKED for the drill to start the hole

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        • #19
          Drills, and I assume similar tools, will wander off if the first contact is too heavy. My technique is to make contact with a light pressure then pause the feed so as to give the drill a chance to 'mill' a divot perfectly concentric with the machine spindle.

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          • #20
            Make sure that locking the table does not move something. Use stub drills if possible, solid carbide drills are better still and could be used as a starting pilot. If you have an optical device to go in the spindle, it can also be used to see if your quill moves when it is locked and unlocked.
            Last edited by old mart; 04-06-2018, 05:45 PM.

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            • #21
              Originally posted by The Artful Bodger View Post
              Drills, and I assume similar tools, will wander off if the first contact is too heavy. My technique is to make contact with a light pressure then pause the feed so as to give the drill a chance to 'mill' a divot perfectly concentric with the machine spindle.
              And split-point is lot less likely to "walk off"

              Some of the Split-point pop rivet drills have very short flutes and make nice spotting drill. And are dirt cheap compared to "real thing"
              Last edited by MattiJ; 04-06-2018, 06:27 PM.
              Location: Helsinki, Finland, Europe

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              • #22
                There is a LOT of merit in the idea someone mentioned above about light pressure.

                I have "drawn" holes back on-center, even with a loose quill, by light pressure and basically letting the drill act as a milling cutter to make a good starting cone before getting into serious drilling pressure.

                heavier pressure does lead to more "walking" of the drill, and even more "wandering" after the drill is started. Some of that may be due to a bad grind, some just to random things like hard spots.
                1601 2137 5683 1002 1437

                Keep eye on ball.
                Hashim Khan

                If you look closely at a digital signal, you find out it is really analog......

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                • #23
                  Gentlemen, TRAM your mills!



                  Originally posted by DEVILHUNTER View Post
                  Had the drilling in place problem when I first started working with my mill. After a while I discovered that the column was tilted, so any time I changed the tool from a short spot drill to a long drill, the point of the tool was in other XY position.
                  Paul A.
                  SE Texas

                  Make it fit.
                  You can't win and there IS a penalty for trying!

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                  • #24
                    What type, or style of mill is being used here?

                    The way I read the OP's problem is that he has started off with using both the center drill and spotting drill, confirmed his spot position location, and then sees the problem when switching to a twist drill to complete the drilling operation. This tool change most likely requires a move of the quill to accommodate a change in tool length. If the machine used is along the order of a traditional Bridgeport type mill then it would most likely be the Z axis of the head not trammed in. If that's the case then the error would be consistent in the same direction.

                    He says that sometimes the holes are off. The head tram could be the problem going from one set up to another set up. If the errors are from piece to piece with the same set up then it sounds like there is movement in the head, or table, that's causing a problem.

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                    • #25
                      Originally posted by J Tiers View Post
                      heavier pressure does lead to more "walking" of the drill, and even more "wandering" after the drill is started. Some of that may be due to a bad grind, some just to random things like hard spots.
                      Tom Lipton (Oxtool) starts the hole then rams the bit through with considerable pressure. He demonstrated this while making a mini pallet. Perhaps it just takes good drills and the right speed.

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                      • #26
                        Yes, nothing says the initial prick punch will be on center.

                        When I punch and drill I:

                        1. Scribe the cross hairs
                        2. Lightly prick punch USING A MAGNIFYING HOOD
                        3. Use a 10X magnifier to check the location of the prick punch
                        4. Lightly punch with a fine punch, tilting the punch to adjust the location of the punch
                        5. AGAIN use a 10X magnifier to check the location of the punch
                        6. Use a larger punch, again tilting it to adjust the location of the punch as needed
                        7. Repeat #5 and #6 as needed to get the punch centered on the cross hairs.

                        With that procedure I can usually guarantee +/- 0.002" or better accuracy for the punch mark.

                        Now even a jobbers length drill can "find" that punch mark and start on it. But, if I want the best accuracy I start with EITHER a center drill or a spotting drill. I find that the results are much the same with either one of them. I mount the part in a drill press vise and allow the vise to float on the table. The short center or spotting drill will center the punch mark under the tip of the drill. I suspect that a center drill will make a better hole for the next drill to follow due to the small diameter hole it drills at the tip. That small hole, made by the tip of the center drill, will be around the web thickness of your next drill which should follow it almost perfectly. So, center drill, pilot drill, and finally full sized drill.

                        Yes, it is a lot of steps, but it does work.

                        When I drill in the mill-drill, first, I have a well trammed mill. No errors due to the length of the drill or the position of the head on the column or of the table on it's vertical slide. Without that, you are just whistling Dixie.

                        Then I find two perpendicular edges with an edge finder. I find that technique is everything with an edge finder. First, I LOCK DOWN any slides that I am not presently using. Thus, while finding the X edge, the Y gibs are LOCKED and visa-versa. If you don't believe this is necessary, try this: put a DTI in a collet in the quill and bring it into contact with an edge. Now grab one end of the table and push it back and forth while watching the needle on the DTI. If it doesn't move 0.005" or more you have a very tight mill table. Locking the gibs on all unused slides will eliminate much of this movement.

                        Then I would find the edges TWICE. Once to get in the ball park and the second time with a lot finer motion on the axis to allow the best possible accuracy in the location of that edge.

                        I often scribe lines on parts that I am going to drill in the mill. This is a double check on the location of the holes, mostly to avoid the dreaded, "one turn" error (0.100"). When I do this, I often find that the holes are offset just a bit from the scribed positions, usually 0.005" or less. For many parts, this is acceptable as the relative locations of the internal features are more important than their relationship to the edges. Such errors are usually about the same for each and every hole or other feature. If not, then I will chase after it when I see that offset when I touch off the first hole. And I have found that this can have many different causes.



                        Originally posted by JoeLee View Post
                        I've seen and had prick punches slide off the scribe line when the point sinks into the steel.

                        JL...............
                        Paul A.
                        SE Texas

                        Make it fit.
                        You can't win and there IS a penalty for trying!

                        Comment


                        • #27
                          The tram issue will only come up if you have to move the table between using the spotting drill, and using the actual drill. If you are just using the quill, there will be no issue unless it is really sloppy.

                          Following a spotting drill (usually short) with a screw machine length drill, will be ideal.

                          Originally posted by CCWKen View Post
                          Tom Lipton (Oxtool) starts the hole then rams the bit through with considerable pressure. He demonstrated this while making a mini pallet. Perhaps it just takes good drills and the right speed.
                          Whatever works.... The key is, both for him and for the situation described by the OP, that you are STARTING the hole with light pressure. After that, you can do as you wish, although "ramming the drill through" is not the best... usually you want to keep enough pressure on for it to cut, but not so much that you begin to split drills, or the like. A sharp drill has a rate of cutting and advance that suits it, and "ramming" with extra pressure is counter-productive at worst, and not helpful at best.
                          1601 2137 5683 1002 1437

                          Keep eye on ball.
                          Hashim Khan

                          If you look closely at a digital signal, you find out it is really analog......

                          Comment


                          • #28
                            Originally posted by J Tiers View Post
                            The tram issue will only come up if you have to move the table between using the spotting drill, and using the actual drill. If you are just using the quill, there will be no issue unless it is really sloppy.
                            While that is often true, you almost never have a situation where the drills are all the same size and don't require moving either the head or knee to change the tools or to get the depth that you need for the hole.

                            It's bad practice to use your mill if you suspect it of being out of tram even one degree. As Paul said, Gentlemen, TRAM your mills!

                            Dan
                            At the end of the project, there is a profound difference between spare parts and left over parts.

                            Location: SF East Bay.

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                            • #29
                              Originally posted by Paul Alciatore View Post
                              Gentlemen, TRAM your mills!
                              This point was covered at some length recently in the CNC section in a thread called 'Albrecht chuck/CNC', and concluded that if the head is misaligned (and it need not be misaligned much) then changing from a short tooling set up, like a spotting drill, to a longer tooling set up can easily result in a misalignment of 30 thou or more.
                              'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

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                              • #30
                                O, to allay any fear of "out of tram" it is 0-0 in the Y axis and out about .0005 in the X axis, to close to mess with. I understand how out of tram works against accurate work.

                                I generally use the spotting drills for larger sizes but for the small ones (3/32 or less) I use center drills. Smallest spotting drill I have found is 1/8" and not much good for small drills.

                                The quill seems OK and the machine (RF-45 bench mill) is not that old at least as far as use is considered.

                                To explain how I pick up the center of a part. I pick up one side and then zero the DRO, pick up the other and then hit the divide by 2 function and dial back to center. Sometimes I use a wiggler, repeating 2 or 3 times with good repeatability and sometimes a 3D Taster (accurate to under a half thou), it doesn't seem to matter.The "spot" always seems to be in the right position. I can lay it out on the surface plate first and use that to verify the "spot" and it will line up OK. I use a small drill to start and then drill to size, sometimes I drill one size under and then finish to size.

                                The weird thing is sometimes I will very close to position (a couple of thou, this isn't a jig borer) and sometimes way out using the same techniques. I guess it is something I'm doing wrong.

                                P.S. I should add that I generally work with small parts, the current ones are 1/4" x 1/4" x 5/8" with a 3/32" hole through one of the 1/4" sides so off center holes stick out.
                                Last edited by loose nut; 04-07-2018, 10:06 AM.
                                The shortest distance between two points is a circle of infinite diameter.

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

                                Southwestern Ontario. Canada

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