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    Advice Needed from a Machinist-gctid822488

    I am in the process of drilling a 3/8" hole in 3/8" thick high strength steel. I do not know the alloy, but it is steel used for rifle and pistol targets. I set it up in my drill press and first drilled a 3/16" hole. I used an old bit that I had laying around, along with a bit of cutting oil. The bit went though the material easily. Next I tried to enlarge the hole with a number of my Hitachi brand, 1/4 and 3/8 bits, some new, some used. They barely penetrated the steel. I then went to the hardware store and bought two Irwin brand, Cobalt bits in 1/4 and 3/8. I got 1/3rd into the hole before the bits were toast. I also tried a titanium coated step drill and it did not work.

    What should I do to drill the 3/8 hole the rest of the way? Are there better bits than Irwin that I should look for? I don't want to keep throwing $$ at this in bits just to find they don't work.
    1999 3788, Cummins 270 "Freedom"
    2013 Boston Whaler 130 SS
    Anacortes, WA
    Isla Verde, PR

    #2
    Not a machinist, but slow and cool is the trick. Slow is obvious but keep using oil. You don't need special expensive drilling oil, motor oil (clean, moderate viscosity say 30W) and don't spare it. Sounds like you bits are getting hot and soft. With unknown alloy, you need something pretty hard for the bit, but it sounds like you know that. But you would not believe how hot high speeds can achieve. I would stop when I stopped seeing shavings.
    Bayliner 195 Bowrider 2013 4.3l 220hp MPI
    Alpha 1, Gen II
    2019 F-150 3.0l Powerstroke Crew Cab 4WD
    Albany, Ohio

    MMSI: 338234042

    King of retirement. Finally got that last promotion.

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      #3
      Go a bit larger on your step. Like nike said, lots of oil, slow rpm and not much pressure. It may be that you are developing some case hardening where the bit heated the metal. That's common and a pain. You sorta have to tease your way through the hard spot. You also want to be using bits that are cut for steel rather than wood or aluminum.
      P/C Pete
      Edmonds Yacht Club (Commodore 1993)
      1988 3818 "GLAUBEN”
      Hino EH700 175 Onan MDKD Genset
      MMSI 367770440

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        #4
        +1 on case hardening and its truly a pain.
        Bayliner 195 Bowrider 2013 4.3l 220hp MPI
        Alpha 1, Gen II
        2019 F-150 3.0l Powerstroke Crew Cab 4WD
        Albany, Ohio

        MMSI: 338234042

        King of retirement. Finally got that last promotion.

        Comment


          #5
          Ar500 steel plates? If making hanging targets, maybe weld chain links on edges.
          Jim, Central pa, '98 2452

          Comment


            #6
            "Norton Rider" post=822488 wrote:
            I am in the process of drilling a 3/8" hole in 3/8" thick high strength steel. I do not know the alloy, but it is steel used for rifle and pistol targets. I set it up in my drill press and first drilled a 3/16" hole. I used an old bit that I had laying around, along with a bit of cutting oil. The bit went though the material easily. Next I tried to enlarge the hole with a number of my Hitachi brand, 1/4 and 3/8 bits, some new, some used. They barely penetrated the steel. I then went to the hardware store and bought two Irwin brand, Cobalt bits in 1/4 and 3/8. I got 1/3rd into the hole before the bits were toast. I also tried a titanium coated step drill and it did not work.

            What should I do to drill the 3/8 hole the rest of the way? Are there better bits than Irwin that I should look for? I don't want to keep throwing $$ at this in bits just to find they don't work.
            The bigger the bit, the slower you have to go. I run " cobalt at 400rpm max. and give it a veritable bath in cutting oil.
            "B on D C", is a 1989 2459 Trophy Offshore HT, OMC 5.7L, Cobra OD, Yamaha 15hp kicker. Lots of toys! I'm no mechanic, just a blue water sailer and woodworker who loves deep sea fishing.
            MMSI: 367637220
            HAM: KE7TTR
            TDI tech diver
            BoD Puget Sound Anglers North Olympic Peninsula Chapter
            Kevin

            Comment


              #7
              Once you work harden it... you're in trouble. You could heat the area to a dull red and then let it cool slowly. That will anneal the metal and soften it a bit. Slow cutting and lots of oil is the trick. Easiest is just to weld a couple of links to it. If you're hanging targets, run down to Harbor Freight and buy a couple of cheap C Clamps to hang them.

              Where are ya shooting plates at?
              Custom CNC Design And Dash Panels

              iBoatNW

              1980 CHB Europa 42 Trawler- "Honey Badger"

              Comment


                #8
                First of all, thanks for the advice. I have an old drill press that changes speeds by by moving the drive belt to different pulley diameters. It's a PITA so I don't change it often. In this case I'll follow the advice and slow the RPM down. I'll try drilling from the opposite direction; maybe I can handle the work hardening this way. If not, I'll try annealing. I have plenty of cutting oil, so that's not an issue.

                The target is a faller that pivots at the bottom. I'm just modifying it by drilling a hole for an eyebolt. The eyebolt will be used to actuate other targets and devices. Eyebolts are preferred to a welded eye because they are easily replaced if damaged. It's one of the targets used at the Marysville Rifle Club for Cowboy Action Shooting.
                1999 3788, Cummins 270 "Freedom"
                2013 Boston Whaler 130 SS
                Anacortes, WA
                Isla Verde, PR

                Comment


                  #9
                  Is it squeaking or chattering when you still?

                  If the hole gets boogered any new bit you stick in catches on the sharp edges and breaks the points off your nice new cutting edge.

                  Start a new hole, you aren't making artwork are you?
                  Esteban
                  Huntington Beach, California
                  2018 Element 16
                  Currently looking for 32xx in South Florida
                  Former Bayliners: 3218, 2859, 2252, 1952

                  Comment


                    #10
                    Like others said it may have gotten case hard from the first drill. Heat as mentioned to anneal or grind the case hardened surface away, or as was mentioned start a new hole. Also be aware that with some steel made from recycled metal there can literally be a bearing ball or roller in there that the first bit just missed. Used to run in to bearing parts even in T-1 when cutting with a torch. It would just blow out around the bearing piece. Try a new hole slow, lubed, and cool.

                    Greg
                    Newport, Oregon
                    South Beach Marina
                    1986 3270 with twin 110 HP Hino diesels. Name of boat "Mr. Darcy"
                    Past work history: Prototyping, tooling, and repair for Reinell,. General fiberglass boat repair starting in 1976.
                    Also worked as heavy equipment mechanic, and machinery mechanic for over 30 years.

                    Comment


                      #11
                      "Mr. Darcy" post=822533 wrote:
                      Try a new hole slow, lubed, and cool.
                      :lol: :lol: :lol:
                      Jeff & Tara (And Ginger too)
                      Lake Havasu City, AZ
                      |
                      Current: 2008 Playcraft 2400 MCM 350 Mag B3
                      2000 Bayliner 3388 Cummins 4bta 250s (SOLD 2020)
                      2000 Bayliner 2858 MCM 7.4 MPI B3 (SOLD 2018)
                      2007 Bayliner 305 MCM twin 350 Mag B3s (SOLD 2012)
                      2008 Bayliner 289 MCM 350 Mag Sea Core B3 (SOLD 2009)
                      And 12 others...
                      In memory of Shadow, the best boat dog ever. Rest in peace, girl. 7-2-10

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                        #12
                        I would suspect work hardening, once you have hardened it it is going to be difficult to get through. In a past life I was a journey level machinist, however many years have passed since.

                        A couple of things to consider high cutting speed produces heat, however slower speeds can break a drill due to chip loading. Favor slower speeds in steel, but use the least amount of pressure that will create a chip. Watch carefully at the breakthrough as it will grab and break the drill. Lots of cutting oil, this is more for cooling than luberication, however lubrication reduces friction and heat. A shop will use a water soluable oil and have it flooding over the area. This creates both lube and heat removal.

                        Not all high speed steel is the same, you get what you pay for, coated M42 grade might work if you don't work harden it, however it sounds like you have already hardened it. Solid carbide will cut through work hardened steel, but may be more expensive than you want to consider. I would not use a step drill for this situation, the step does not have a strong cutting edge and will fail quickly. The step is typically for finish cutting and sizing , not rough cutting.

                        If you are almost through and hole precision is not critical consider a dremel bit grinder to finish it out.

                        If the precise location is not critical for balance or some other reason. I would recommend moving the hole. You indicated it is a 3/8 dia, rule of thumb is move at least 2x the diameter.

                        Another option if it must be located specifically for balance, or other reason could be cut out the area with a torch and weld in a patch plate and drill it.
                        4788 PH 2001, Cummins 370's

                        MMSI: 338013392
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                        Exploring the Salish Sea

                        Comment


                          #13
                          Norton, if you want to come to Mukilteo you can use my vertical mill. It might take some minor digging to get at it, and it's a manual, but it will do the job. Do you know if Mike and Carol Delong are involved with that group? I know Mike does some western shooting.
                          P/C Pete
                          Edmonds Yacht Club (Commodore 1993)
                          1988 3818 "GLAUBEN”
                          Hino EH700 175 Onan MDKD Genset
                          MMSI 367770440

                          Comment


                            #14
                            "Knot Happy" post=822684 wrote:
                            I would suspect work hardening, once you have hardened it it is going to be difficult to get through. In a past life I was a journey level machinist, however many years have passed since.

                            A couple of things to consider high cutting speed produces heat, however slower speeds can break a drill due to chip loading. Favor slower speeds in steel, but use the least amount of pressure that will create a chip. Watch carefully at the breakthrough as it will grab and break the drill. Lots of cutting oil, this is more for cooling than luberication, however lubrication reduces friction and heat. A shop will use a water soluable oil and have it flooding over the area. This creates both lube and heat removal.

                            Not all high speed steel is the same, you get what you pay for, coated M42 grade might work if you don't work harden it, however it sounds like you have already hardened it. Solid carbide will cut through work hardened steel, but may be more expensive than you want to consider. I would not use a step drill for this situation, the step does not have a strong cutting edge and will fail quickly. The step is typically for finish cutting and sizing , not rough cutting.

                            If you are almost through and hole precision is not critical consider a dremel bit grinder to finish it out.

                            If the precise location is not critical for balance or some other reason. I would recommend moving the hole. You indicated it is a 3/8 dia, rule of thumb is move at least 2x the diameter.

                            Another option if it must be located specifically for balance, or other reason could be cut out the area with a torch and weld in a patch plate and drill it.
                            Thanks for the advice. I was actually thinking of using a couple of aluminum oxide grinding stones that I have for my Dremel to grind through the hardened metal. Hole precision is not an issue in this case.

                            As you and others have pointed out, I may move the hole, since the location is not critical. I used to live by the mantra of 2D-ED (2 diameters edge distance) when I was an aerospace Liaison Engineer many years ago
                            1999 3788, Cummins 270 "Freedom"
                            2013 Boston Whaler 130 SS
                            Anacortes, WA
                            Isla Verde, PR

                            Comment


                              #15
                              "Pcpete" post=822692 wrote:
                              Norton, if you want to come to Mukilteo you can use my vertical mill. It might take some minor digging to get at it, and it's a manual, but it will do the job. Do you know if Mike and Carol Delong are involved with that group? I know Mike does some western shooting.
                              Thanks for the offer. Let me see how far I get with the other suggestions and I'll let you know.

                              I may know the Delongs, but I don't know for sure. We all use aliases in cowboy action shooting. Often we'll shoot with people for years without ever knowing their real names. My alias is "El Vasco." In English this means "The Basque One."
                              1999 3788, Cummins 270 "Freedom"
                              2013 Boston Whaler 130 SS
                              Anacortes, WA
                              Isla Verde, PR

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