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Accurate drilling - received wisdom

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  • #16
    Originally posted by Mcgyver View Post
    a fools errand? You musn't be doing it properly - whats going that its not working for you? I have a newall dro and large(ish) vmc but there are many times that manual layout and punches on the drill press are a lot faster. Same with transfer punches & drill press (done the same way, but a mark from transfer punch instead of scribed lines) heck, a lot of time (like yesterday, making a small bracket) you don't even lay out - eyeball location, punch and drill.

    The trick is to pick the right tools and approach for the job at hand and understand the accuracy capabilities and strengths/weaknesses of each. The more you're capable of, the better able you will be to select the right one.
    Everything I do requires locations within .003" Model making, and small parts have no room for error. I never claimed it was faster, but I insinuated that it is indeed more accurate.
    I do not do this professionally, thank god, I do not like to work fast. I have to admire you guys that can do this stuff accurately AND quickly.

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    • #17
      Originally posted by RB211 View Post
      Everything I do requires locations within .003" Model making, and small parts have no room for error. I never claimed it was faster, but I insinuated that it is indeed more accurate.
      I do not do this professionally, thank god, I do not like to work fast. I have to admire you guys that can do this stuff accurately AND quickly.
      I probably can't work to a thou any faster than you can and when making models agree x/y layout (dial or dro) or CNC is great....but if the last job I did was dozens of lag bolt holes 1.5" angle iron welded shelf brackets....then read punch and drill and is a fools errand...I kind of go something is missing here. But we're on the same page, it came across as universal indictment but I get now you meant in the context of your work.

      On speed, I'm not racing a hourly clock either ....thank goodness is right.....just the big clock. Its not pressure that takes the fun away, just I'd rather get more done in a block of time. So....I don't want to use processes that strive for more accuracy than the the job requires
      Last edited by Mcgyver; 05-25-2017, 04:32 PM.
      in Toronto Ontario - where are you?

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      • #18
        Select a method suited for the to be accomplished (machining, iron work, carpentry, plumbing, etc,) no more - no less. IOW make the punishment fit the crime...

        here's a musical lesson:

        https://www.youtube.com/watch?v=Ip6czeTuNEU

        There is no one way to do anything, some are ingenious, some preferred, some expedient, some wasteful, lame, or silly. Searing declarations of the Right Way tempts Fate if not heralding a Darwinian loss of face from the emergence of a superior, simpler, lower cost alternative as from the mouth of a child.
        Last edited by Forrest Addy; 05-25-2017, 08:06 PM.

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        • #19
          Originally posted by CalM View Post
          If the subject is drilling on the lathe, Always bore the first 5 mm depth if the hole location is important.
          I've never heard this before. Is it to compensate for tailstock alignment errors?

          David...
          http://fixerdave.blogspot.com/

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          • #20
            Originally posted by boslab View Post
            Same applies to tungsten electrodes.
            There's a further way, use a jig and drill bush, fairly accurate, one jig can have several bushes, you set the jig relative to the datum edges of the job, aka jig drilling
            Mark
            Agreed, but you still have to make the jig

            I did mention that as a way of making parts that will line up with each other.

            Mostly, this is an experiment to see if I can actually communicate something clearly and concisely... without writing my typical 1000 word essay. It's very hard for me to stop writing once I get going

            David...
            http://fixerdave.blogspot.com/

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            • #21
              Originally posted by fixerdave View Post
              I've never heard this before. Is it to compensate for tailstock alignment errors?

              David...
              Nope, it's to give the drill or reamer the most concentric start possible.

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              • #22
                It is looking like I'm the only one that does not center punch any thing to be drilled on a no-dro mill. I locate the scribe line cross section with a 20 degree sharp pointed rod held in the drill chuck. Then start the normal drilling process. It seems to me to be easier and more accurate than to locate the in the center of a punch crater which may or may not be accurately placed to begin with.

                Come to think about it I don't use punch marks on the drill press since I added an x-y mounted vice there.

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                • #23
                  Good enough is good enough, but take a look at the drill point

                  Originally posted by rickyb View Post
                  It is looking like I'm the only one that does not center punch any thing to be drilled on a no-dro mill. I locate the scribe line cross section with a 20 degree sharp pointed rod held in the drill chuck. Then start the normal drilling process. It seems to me to be easier and more accurate than to locate the in the center of a punch crater which may or may not be accurately placed to begin with.

                  Come to think about it I don't use punch marks on the drill press since I added an x-y mounted vice there.
                  Then take a look at the "spot" the drill point leaves when you just touch down and go into steel about .005"
                  Have a look with magnification.

                  There are good reasons why wigglers and center punch methods were developed. Twist drills are much too flexible to be relied on to hold position.

                  Drill a piece of hot rolled with a 3/32 jobber drill. With no center punch divot to follow, the drill tip will walk around like a drunk. '=))

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                  • #24
                    Originally posted by CalM View Post
                    Then take a look at the "spot" the drill point leaves when you just touch down and go into steel about .005"
                    Have a look with magnification.

                    There are good reasons why wigglers and center punch methods were developed. Twist drills are much too flexible to be relied on to hold position.

                    Drill a piece of hot rolled with a 3/32 jobber drill. With no center punch divot to follow, the drill tip will walk around like a drunk. '=))
                    I didn't expand on it, but to me the "normal drilling process" is to first center drill a pilot.

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                    • #25
                      Sounds like some people want to converge on a single "approved" way of drilling holes; no deviation allowed. I thought about the ways and requirements I use for drilling holes and gave up at a dozen from hanging pictures to roughing holes undersized for later boring to precision size and location.

                      An as-drilled hole is seldom a precision cylinder. Its size is inevitably 0.003" to 0.010" larger then the drill, the finish is a usually a bit rough and seldom very round, and it may be lobed, bell-mouthed, rainbowed, or mis-located because of walk before actual penetration. An as-drilled may be used for clearance on bolts, as an initial step for reaming or boring, tapped or bored for threaded fasteners, passage for liquid, to reduce weight, waste out excess material, etc. And that's just in general machine shop applications

                      Aint no one rule for drilling from layout by hand or machine any more than one size drilled hole fits all. I like to think I pick the simplest, handiest, and most efficient way to make a hole that suits the job and the available equipment. If you have a preferred way to drill holes, well and good but don't sneer at a fellow who uses a slightly different method - or many. If it works for the other guy, well and good. If the guy is a noob or not so experienced and off on a tangent for some reason, a polite suggestion is plenty.

                      However I'm an old fart of 75 with long and diversified experience in most forms of metalworking so naturally I can throw my weight around. When I do it, i'm an adorable, delightful grouch. If you guys try it, people think you're a PITA.
                      Last edited by Forrest Addy; 05-28-2017, 08:09 AM.

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                      • #26
                        Originally posted by Forrest Addy View Post
                        Sounds like some people want to converge on a single "approved" way of drilling holes...
                        Actually, my goal was to differentiate between 2 different approaches, while not saying either was better nor that they were the only ways.

                        I suspect I'm not alone in doing a reasonably precise layout, getting a nice center punched mark, then cramming a center drill into it by eyeball, locking everything down to drill, and then wondering why the stupid hole isn't in the place I wanted it. I was stupidly mixing approaches, taking a little from both ways, and not getting the results I wanted. If I had left it at a fine punch mark and then used that with a measuring tool, like a center finder, before locking everything down for the center drill (the index method) OR if I had used a jobber-length drill in that center mark and let everything float, the hole would have ended up closer to where I wanted it. Just an "aHA!" moment that I'd figure I'd write down in an coherent way. That, and a few other tips I've come across in reading.

                        David...

                        Edit: now posted: Drilling Holes in all the Right Places
                        Last edited by fixerdave; 05-27-2017, 09:46 PM.
                        http://fixerdave.blogspot.com/

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                        • #27
                          Here is to old farts!

                          I have not obtained such august status yet. But I can see it from where I am standing.

                          I began my engineering career in a company that had a shop filled with experienced machinists and tool and die makers. Most were close to retirement in the early 80's. I learned so much from them. I still remember Max Pfluger saying with his thick German accent, "The hole is not complete until it has bin deburrrrrrrrrred" Last step is always a counter sink or a deburring tool depending on hole diameter.

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                          • #28
                            Originally posted by Erich View Post
                            ..."The hole is not complete until it has bin deburrrrrrrrrred"
                            THANKS...

                            I was drilling some holes today... that just kept running through my head, over and over and over and over and over, in my best German accent, which I must admit probably sounds more like Swedish. Never was any good at fake German, even in my head.

                            I wonder how long that's going to last??

                            David...
                            http://fixerdave.blogspot.com/

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                            • #29
                              I do it old school. Layout on surface plate with a height gage, prick punch, then punch. Inspect punch marks with a magnifier for accuracy, adjust if needed. Then my personal touch is to go over it with a flat file to remove the ridges. My thought there is that if I have to move a punch mark the ridges might be uneven and cause the drill to wander, especially in soft material.

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                              • #30
                                I do it the old school way too. Then, when I try to bolt the carefully laid out and drilled parts together, the bolts don't go. So I drill all the holes oversize.

                                There, fixed!

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