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small boring bar? HSS??

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  • small boring bar? HSS??

    I need to make a small boring bar (under 3/8") and was wondering if any of you have ever made one out of a HSS drill bit? Thanks.
    Russ
    I have tools I don't even know I own...

  • #2
    I've seen it done and possibly done myself over the years. The big question is just how deep do you need to go
    Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.

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    • #3
      I only need to go in 3/8". I bought a set of those "trick" brazed carbide boring bars. They work perfect for what I'm doing but the carbide must be a new lead alloy...lol! They dull after a few passes in mild steel. So it's back to HSS. I have a pile of old drill bits and was wondering if they'd work. Thanks.
      Russ
      I have tools I don't even know I own...

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      • #4
        Most HSS tool steel makers offer straight round HSS blanks in nominal diameters. The enco catalog offers 3/8" dia x 5" sticks for $2.30 (Model 383-7030).

        I've heated up these round sticks to yellow heat and forged a little short crook at the end so I'd have something to grind a tool shape on. Cool them to black with an air hose and they're hard as ever.

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        • #5
          If you don't have the access to the flame wrench as Forrest suggest I think the best thing to grind a boring tool out of would be an old worn out or busted tap. I've found I can even make small diameter roughing mills out of one by grinding cutting and back lcearance on the flutes
          Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.

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          • #6
            Spin, Forrest...thanks! I just tried a drill bit. If I knew how to sharpen it right it would work well. Tried a couple different profiles and have one that works but chatters around .015 DOC...must be the flimsy twist in the bit. I'd use the solid stuff if I had it. A tap would be better I'm sure due to the lack of twist. I'll try it in a bit.
            Russ
            I have tools I don't even know I own...

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            • #7
              I use old end mills for small shallow bores like that. They are already ground properly, you just have to get one of the flutes set on center. I set it in the #2 tool holder for the QCTP (the one with a V-groove in the bottom) and it works OK for my purposes.

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              • #8
                <font face="Verdana, Arial" size="2">Originally posted by Forrest Addy:
                Most HSS tool steel makers offer straight round HSS blanks in nominal diameters. The enco catalog offers 3/8" dia x 5" sticks for $2.30 (Model 383-7030).

                I've heated up these round sticks to yellow heat and forged a little short crook at the end so I'd have something to grind a tool shape on. Cool them to black with an air hose and they're hard as ever.
                </font>

                Thanks for the tip Forrest, I was always under the impression that if you did that to HSS it would ruin it. I'll definatly give it a try sometime.
                To invent, you need a good imagination - and a pile of junk. Thomas A. Edison

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                • #9
                  Like Nutter, just use an end mill.

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                  • #10
                    Don't remember where I got 'em (probably an auction), but I have 3 or 4 'boring bars' someone made of regular square lathe tool bits, by grinding a substantial radius on the lower left corner, as you look from the back, for an inch or so. Looking at the cutting end they're about a quarter circle. Took a lot of grinding, but they really work great.
                    Lynn (Huntsville, AL)

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                    • #11
                      Nutter's got it right.
                      I've ground endmills down below 1/8" for tiny bored and tapered holes.
                      Grind the back flute away, grind the top flat plus a little rake, and a little clearance on the front flute and front face.
                      kap

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                      • #12
                        Milling cutters are better as most drill shanks are soft so they can be grabbed by the hardened jaws of a chuck. Dowel pins can be used as they are hard. Drill rod is also quite cheap and if heated will bend quite sharply and then can be heat treated with a torch. If you are wanting accuate holes of the same size you can purchase machine reamers in every decimal size at a reasonable price and then just drill and ream without worrying about the bar flexing or having a slightly tapered hole. The hole will be bang on every time.

                        Mike

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                        • #13
                          Thanks guys! This wasn't a high tech job and the drill bit worked fine after I got it sharpened right. I had 10 pieces that the holes had been drilled off center so had to true them up before drilling to the proper size. No suprise I guess that the drill bit cutter outlasted the chinese carbide boring bars.
                          I have tools I don't even know I own...

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                          • #14
                            Torker;
                            use a #3 or #4 broken center drill.
                            grind the point like a boring bar set to center put a angle or small radius on the point.
                            measuring frequently rough .050" to .100" on bore size to w/in .020" for final cut on bore.
                            after boring to w/in .050" on dia. start working the depth of the floor by increments of .010" leave .005" to finish on the depth of a counterbore.
                            at the same time remove the .050" on the bore at .010" to determine size. then bore .020" more and check this size then take the finish cut on bore diameter and the .005" on the floor at the same cut you may have to reverse the cross slide gear to feed in.
                            inspect to print and rework immediately if needed.
                            EX: bore target .375 actual .368 remove bore maerial after touching off using dykem or magic marker note touch off point allow .001" if you touched off light.
                            remove tool away from bore.
                            take all backlash out of cross slide and return tool to touch off point plus .006" and bore to depth.
                            notate bore and depth for next parts.
                            use 750 RPM.
                            rough feed .010" to .015" per rev.
                            finish feed .005" to .0075" per rev.
                            RPM is for 75 sfpm 0-1 tool steel.
                            1018 steel increase to 90 to 95 sfpm.
                            for aluminum increase to 125 to 150 sfpm.
                            for stainless reduce to 30 to 60 sfpm.
                            hope this helps...jim
                            ...jim

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                            • #15
                              This is the smallest boring bar that I use, it is a piece of 3/16" HSS round blank. It is mounted in the toolpost on a piece of 1/4 x 5/8 flat bar with a V milled into it.


                              I have a few different sizes of round hss specifically for small hole boring. I guess one day I'll end up with a 1/16" bit too

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