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Problems CounterBoring

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  • Problems CounterBoring

    I have been doing some counterboring (actually a LOT of IT Lately) I took on a Contract Position at a temporary agency as a Tool Room Machinist. I HAVE done a LOT of tool steel drilling and counterboring in the Past BUT i have NEVER had the amount of troubles ive encountered with this Material i am now working on. It is A-2 and i counterbore 1/2 inch diameter for 9.5 inches deep. I make extendsions up and am presently running 125 rpm, at .005 thou per rev feed. Anything else just wouldnt even work. As it is it is jumpy all the way through the blocks. I have tried putting a LOT of pressure on it to get it to bite in and stoop its jumping but nothing seems to work? HM?? Just curious what youd suggest ourt tooling isnt the best there but ive not had this problem before >? Any Hints Guys ? Thanx Mike

  • #2
    I presume the counterbore is because they need the flat bottom hole down there at the 9-1/2" depth. But that doesn't mean that the whole depth needs to be produced by the counterbore. I'd be inclined to drill down 9-1/4" with a regular twist drill that can be resharpened much more easily and just hit the bottoms of the holes with the counterbore.

    I'd also be suspicious of the cutting edges of the counterbore after that much work in A2 and that would be consistent with what you're experiencing. If they can't or won't get the tool resharpened if it needs it, can you do a little judicious dressing with a Dremel tool?
    .
    "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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    • #3
      2X on TG's recommendation as its exactly what I would have said.

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      • #4
        Counterboring

        I would get a long spade drill that uses replaceable carbide tips. The carbide comes in pointed and flat end. Drill most of the way with the pointed end, then change to the flat end to finish up. You will still need to keep the RPM reasonable and use coolant or oil to not burn up bits, but it would go a lot easier. I prefer the AMEC brand of spade drills.

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        • #5
          My first thought would be dull tool.
          Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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          • #6
            A 9 1/2 " counterbore? Why? The purpose of a counterbore is normally to put the head of a fastener flush or below. It sounds like you need fasteners 9 inches longer and a new engineer. 9 inches is approaching gun drill territory. A counterbore is not intended for such use. The solution may be as above to drill part way and finish with the counterbore. If the drill wanders then your pilot on the counterbore may not line up or be in a bind, resulting in a broken counterbore stuck in an obviously expensive workpiece.

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            • #7
              Drill wandering is certainly a possibility on a deep hole, but I'd think the concentricity wouldn't be much of an issue here. If he drills the smaller diameter first, it will tend to keep the 1/2" drill following the small diameter wherever it may lead. And if he drills the larger diameter first, he's got the cone of the drill to help center the smaller diameter tool. A little more iffy in this case since the web will leave something more like a shallow concavity rather than a center drill or spotting drill start but probably sufficient.
              .
              "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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              • #8
                I agree with tgmidget, why in the world would a real engineer do that in A2 steel. That borders on ignorant and tells me he don't know what he is doing. Just use a long bolt.

                That's about the dumbest thing I have ever heard. A2 is hard enough to work with without making it even harder to do.
                It's only ink and paper

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                • #9
                  Engineers??

                  Well i DO agree with you guys BUT in the world of contract Machining do like the print. I do like the idea of the larger drill to suit the bore xcept for the last 1/4 inch or so. I been drilling counterboring a toin of stuff and this shops the first time i have had these things occurr. Thanx Mike

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                  • #10
                    OH

                    This is why im there to do all the stupid things they arent willing to i guess? Sometimes i just want to give up. Later Thanx Mike

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                    • #11
                      I presume the counterbore is because they need the flat bottom hole down there at the 9-1/2" depth. But that doesn't mean that the whole depth needs to be produced by the counterbore. I'd be inclined to drill down 9-1/4" with a regular twist drill that can be resharpened much more easily and just hit the bottoms of the holes with the counterbore. -TGTool
                      *** TWO THUMBS AND A BIG TOE UP ***

                      I agree with tgmidget, why in the world would a real engineer do that in A2 steel. That borders on ignorant and tells me he don't know what he is doing. Just use a long bolt. - Carld
                      Carld, I routinely work with PhDs and trust me there is no correlation between a title appended to a name and basic common sense. The best way I've ever heard it put is ... They have a lot of intelligence and no brains.

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                      • #12
                        "Drilling 9 inches is one thing, but COUNTERBORING 9", wow that's going to cost you a whole lot more."

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                        • #13
                          I agree with the idea of drilling 9 1/4 inches and then counter boring the last 1/4". I have a couple of drill bits sharpened with flat bottoms that I use for precisely that purpose. Drill with a standard drill and clean up/ flatten the hole with the square bit. Not difficult to sharpen off-hand either.

                          While I rarely bother to defend engineers, for those slagging off at them I'll mention a lesson that was taught to me many years ago by one of my better bosses. I walked into his office one day complaining about a stupid design and he sat me down and proceeded to ask me a series of questions about the design and what it was intended to do. After a short time of me revealing my total ignorance, he pointed out that only the designer knows exactly what a design is intended to achieve and why it was done that way. While the rest of us might think we could do better, as soon as we do we take on all liability and responsibility for the item, which as we don't know why things were done that way in the first place, may even be more likely to fail. I've met some abysmal engineers but I've also met some great ones who's good ideas have been derailed by tradesmen who knew better...

                          As an example, I once worked in a machine shop with 6 or so machinists. There was one medium sized lathe there that no one wanted to use as the compound slide screw was tight in one spot when it revolved. It had been like that for ages. It took me all of 15 minutes examine it, take it apart and find the high spot where the screw had been bent and straighten it. After that, every one said that it was fine. I hadn't trained as a fitter, but I did wonder why one of the machinists (some with 20+ years of experience) there were not able to diagnose and fix this relatively simple problem.

                          Back to the issue at hand, I can think of at least two reasons why a deep counter bore might be better than a long bolt, and (with apologies for any offense caused to Mike) if someone came to me saying that they had to cut 9 1/2" with a counter bore, I'd be wondering why they didn't drill most of it in the first place before I called the designer ignorant.

                          Michael
                          (Mindful that there but for the grace of God go I...)

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                          • #14
                            form_change, I agree with what you say. Had I been given that job I would have asked to talk to the designer/engineer and asked why it needed to be counterbored 9 1/2" deep. I would have then suggested alternative ways that would be better and faster. Had he/she refused those suggestions I would have told him the cost to do it as designed would be high and on his dime.

                            Since madman is working for them and not doing it in his shop when the shop finds out how long it takes and how many counterbore cutters it takes they WILL convince the engineer to change his plans if cost is an issue.

                            If the cost to do the job is no problem let the work begin and the customer pays for time, material and cutters.

                            Many was the time I was given a job and when I looked it over I would tell the shop owner this is not the best way and will take a lot of time. He would look it over and decide whether to work it out with the customer or just do it and charge him as needed. Most the time when a customer found out the cost was to be high they decided on changes as needed.
                            It's only ink and paper

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                            • #15
                              Yep,counterbores were not designed to do deep hole drilling. Can you get a regular type long drill ground with a pilot on it's tip? That will keep the drill from wandering. But,drilling the holes with successively larger drills till you get to the one you need will also help keep the hole centered. Of course,they'd all have to be long drills.

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