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A Really Boring Subject

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  • A Really Boring Subject

    I just replaced my Number Set of Drills and am some what confussed by what I got. The set I had was a hand-me-down so I didn't have much confidence in sizes of the drill in the set. However, I decided to check the diameters of the drills in the new set against the diameter they are suppose to be.

    In almost all of the cases, the actual diameter of the drill was about 0.002" to 0.003" undersize for that specific drill. For example, the #29 drill is suppose to have a diameter of 0.1360", but the #29 drill that came in my set has a diameter of 0.133". There are a few drills that are off by as much as 0.005". The drill in the #6 slot has a diameter of 0.199" while the #6 drill shoud have a diameter of 0.204". Is this suppose to be the case? Are all the drills slightly under sized or is it a function of the makers of the set of drills I purchased?

    The set does have other problems as the drills in the #48 and #49 slots have identical diameter of 0.075". The same was true of #9 and #10 drills with each having the same diameter of 0.193". The drills in slots # 60 and #58 have the same diameter of 0.040" and the drill in the #59 slot has a diameter of 0.038"!

    I would like to know if I'm just picking at nits or should I have invested a lot more money and gotten a set of drills made in the USA? Appreciate any help. Thanks.

    Bill
    Bill

    Being ROAD KILL on the Information Super Highway and Electronically Challenged really SUCKS!!

    Every problem can be solved through the proper application of explosives, duct tape, teflon, WD-40, or any combo of the aforementioned items.

  • #2
    Definately you should have a set of accurate measuring drills. To drill a hole for thread tapping, you must have accurate hole sizing. The smaller the tap the more important this gets. Buy made in USA good quality!!! JIM
    jim

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    • #3
      Originally posted by BigBoy1
      ...I decided to check the diameters of the drills in the new set against the diameter they are supposed to be...
      What did you actually check and how did you check it? AIUI, drill shanks generally are a small bit undersize. It's also quite difficult to measure across the flutes as the pressure of the micrometer tends to rotate the drillbit.

      Can you drill a hole with each bit and try with a pin gauge (you were the one who said it was boring!)? As a final thought, it's generally said that twist drill produce oversize holes, so would an undersize bit produce a correct hole?

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      • #4
        The shanks will be small because of the backtaper built into the drill. Always check the drill size by measuring/gaging at the cutting end.

        Comment


        • #5
          In my experience, the only way to measure accurately, is to drill a hole and use plug gauges.
          Just got my head together
          now my body's falling apart

          Comment


          • #6
            It sounds like you got a set of mismatched drills. The best way I have found to measure drills is with dial calipers and put the drill in the jaws so the drill contacts the full length of the jaws. That way the twist of the drill does not affect the measurement of the diameter.

            If you can send them back do so and get a quality set. They should be within a 1/2" thou. +/-.
            It's only ink and paper

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            • #7
              Swarf,

              Originally posted by Swarf&Sparks
              In my experience, the only way to measure accurately, is to drill a hole and use plug gauges.
              The size of the hole relates as much to drill size, as to proper
              grinding of the cutting edges, and the material as well.

              The drill will frequently cut smaller when the tip breakes thru as well.

              I'm just curious, what your experience level in the trade is?

              Kap

              Comment


              • #8
                I have a set of quality USA Cobalt and a cheap set of the , well you know. Both measure a couple thousands under. If a precise hole is required you will not be using a drill for the finish size anyway. For tapping a thousands on each side is not going to mean a hill of beans to virtually anything the home shop machinist is likely to be tapping.

                My opinion, guess I'm still entitled to it

                Comment


                • #9
                  Replies

                  My measuring method was to measure the shank of each drill with dial caliper.

                  I don't have a plug set so that method can not be used.

                  I've only just really got into machining as I went to Grizzly and picked up my milling machine after the last Cabin Fever show. Have be working at if for about 8 months. I'm still in the tool acquisition phase. (From the posts I have read, that will last the rest of my lifetime!)

                  Will look into getting a good USA set for when the "good" work is being done.

                  Thanks.

                  Bill
                  Bill

                  Being ROAD KILL on the Information Super Highway and Electronically Challenged really SUCKS!!

                  Every problem can be solved through the proper application of explosives, duct tape, teflon, WD-40, or any combo of the aforementioned items.

                  Comment


                  • #10
                    I always use a drill hole gage to check my drill bits. I have 3 hole plates....Alphabet, numbered and fractional with a set of American made bits for each.
                    I have not seen undersize drill bits before so I assume you just got burned by not buying Made in USA bits. The bright side is what you bought were cheap, so while we all do not like throwing money away, it was an inexpensive lesson learned at least........pg

                    Comment


                    • #11
                      More Tools

                      Originally posted by piniongear
                      I always use a drill hole gage to check my drill bits. I have 3 hole plates....Alphabet, numbered and fractional with a set of American made bits for each.

                      See! More tools are needed. I'll add the drill check to my list of things to get. Between materials and new tools, my credit card can't take the strain much longer. I may have to try to turn the hobby into a "paying" hobby.

                      Bill
                      Bill

                      Being ROAD KILL on the Information Super Highway and Electronically Challenged really SUCKS!!

                      Every problem can be solved through the proper application of explosives, duct tape, teflon, WD-40, or any combo of the aforementioned items.

                      Comment


                      • #12
                        "I'm just curious, what your experience level in the trade is?"

                        drilling enough holes in 316 to make a bloody big tea strainer.

                        Apart from that, does "cementation" mean anything to you?
                        The guy that checked my work used to diamond paste lap their dies.
                        Just got my head together
                        now my body's falling apart

                        Comment


                        • #13
                          Originally posted by BigBoy1
                          I may have to try to turn the hobby into a "paying" hobby.

                          Bill
                          OOO-hh....don't make that mistake. When you accept money it ceases to remain a hobby and turns into labor. Been there done that......pg

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