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Recommendations for a boring bar for flat bottomed hole?

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  • Recommendations for a boring bar for flat bottomed hole?

    I'm looking for a boring bar that can bore a flat bottomed hole? Are there any carbide insert ones, or should I just grind a hss one?


    Benjamin

  • #2
    There are literally hundreds of insert types, but... what diameter, depth and material?

    Please fill in your profile location... not much point in giving you my local link if you are in Zimbabwe.

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    • #3
      Best recommendation is to avoid such a tool if possible, potential for massive cha-cha-chatter.

      If possible use cross feed to flatten the bottom.

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      • #4
        In general, I drill first, then enlarge with a boring bar. Either an end mill or a spade bit will drill a flat bottom hole that you can then enlarge with a boring bar.

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

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        • #5
          How wide is the flat bottom?

          Center cutting end mill and plunge if the cutter od matches your print.

          Center the hole on a rotary table and use an endmill to pocket your hole.

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          • #6
            Location duly filled in.

            Perhaps I didn't make my question clear enough. What I'm trying to do is bore a 2.5" hole with a flat bottom, but from my understanding, not all carbide insert boring bars can flatten the bottom. I'm also seriously considering just getting 5/8" HSS round blank and grinding a boring bar to shape.

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            • #7
              Originally posted by benjaminh View Post
              Location duly filled in.

              Perhaps I didn't make my question clear enough. What I'm trying to do is bore a 2.5" hole with a flat bottom, but from my understanding, not all carbide insert boring bars can flatten the bottom. I'm also seriously considering just getting 5/8" HSS round blank and grinding a boring bar to shape.
              2.5" depth? Diameter?
              Most carbide insert boring bars will flatten the bottom with cross-feed, SCLCR or SDUCR being common types.

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              • #8
                2.5" diameter, 2" depth...

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                • #9
                  Assuming you drill a hole first then open it up to 2.5. My process would be to bore out to .01 to .02 smaller than the diameter you wish. And at the same time to roughly .02 to .03 shy of the intended depth. You'll need to rig up some indicators or other measurement devices to measure and track the carriage movement.

                  Then I'd center or nearly center the boring bar and run it to full depth then move it outwards to the under size bore diameter. Then clean up the diameter of the bore with what it takes and this time run it to the full proper depth. This way you're never really trying to bore into the corner and end up with the chatter the others warn about.

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                  • #10
                    I'm afraid I'm going to have to start with a 3/4" or 1" drilled hole, as my small lathe couldn't handle a 2" bit...

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                    • #11
                      Originally posted by benjaminh View Post
                      I'm afraid I'm going to have to start with a 3/4" or 1" drilled hole, as my small lathe couldn't handle a 2" bit...
                      Machining a 2.5" dia. 2" deep is a fairly straight forward operation on a lathe. It's pretty much the same as turning a diameter to a square shoulder, only you're doing it on an inside hole. Start with the 1" drilled hole and start boring it out with as big a bar as you have. A 1/2" bar shank should be plenty strong enough to project out from the tool holder for the 2" depth requirement. The cutter end geometry should have a relief angle on the end so the bar can make a facing cut from small to larger dia. Do you have a method of tracking carriage movement for holding the 2" depth? If so, start boring the hole, taking as big a cut as you and the lathe can handle, and bore the hole to a depth of about 1.980. When you've made the finish cut for the 2.5" dia. note the number reading on the cross slide dial, then position the bar at the final 2" depth and face the bottom of the hole, cutting from the center out to the number that gave you the finished dia.

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                      • #12
                        these work fine
                        http://www.micro-machine-shop.com/boring_bar_set_1.jpg

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                        • #13
                          Originally posted by benjaminh View Post
                          I'm afraid I'm going to have to start with a 3/4" or 1" drilled hole, as my small lathe couldn't handle a 2" bit...
                          That's what I expected and likely what we'd all do. If you don't want the center cone dimple at the end of the hole be sure you limit how far in the drill bit goes.

                          That's a pretty shallow bore all things considered. So you should be OK with a relatively slender boring bar and a 3/4" starting hole. You'll also have the benefit of seeing what you're doing at the base of the hole.

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