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Boring Bars & Tool Holders

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  • Boring Bars & Tool Holders

    This may sound silly to some of you ole-timers but i need help with these. I have a smithy 1220xl, It has a turret style tool holder (4-way). With clamp down screws to hold the tool. Tool slots are 5/8" High.
    Some tools work in this type holder some won't i understand. I need a cut-off tool and a set of boring bars. I prefer to use indexable tooling because i really don't feel comfortable grinding my own tools yet.
    For example, now i need to bore a cyl. 2" deep(through) and 1.000" i.d.
    I have a miniature bar that will not reach the 2" depth, And i bought one from grizzly that i thought would work. It is 3/4 wide and 5 ins. long but the angles allow it to rub under the point of the cut,when on center.
    If you Could just elaberate a little on the subject of choosing the right tool and the different means of holding them.
    Such as, I thought about a rocker type toolpost but it wouldn't hold a square carbide tipped tool like i use. With so many choices available i get lost with what i am looking for....
    Ant input would be very helpfull, Thanks....

  • #2
    Your turret toolpost is fine and there are many boring bars that should work. I'd stay with the positive rake bars myself. Get a Travers catalog and look at what's available.

    A low cost alternative are the long round double ended bars that take square tool bits. These are very versatile and grinding tool bits is not rocket science, so jump in and get started.

    You might try that Grizzly bar again but set it a bit above center so it doesn't rub.

    The rocker toolposts take Armstrong type tool holders which take square tool bits. I used these for many years and they work well. I prefer the turret post now I think since I use the indexable stuff mostly.


    • #3
      The boring bar you speak of may require a larger hole than you are boring to start the hole. I have a 1 1/4" boring bar but it requires a 1 1/2" hole for clearance to bore a 1.5+" hole.

      You should also note that in general a steel boring bar should not be used to bore more than 5 times as deep as the diameter of the boring bar (this is called "overhang"). Solid carbide boring bars can go to 11x overhang and tuned boring bars (anti-resonance heavy metal bars) can go much greater overhang for a much greater price. Therefore, although my 1-1/4" bar is 14" long I should "only" bore a 6" deep hole.

      To help cut down chatter the boring bar is best clamped by its entire circumference (like a collet) with minimum overhang. Although boring bars have clamping flats for screws, this is the least preferred clamping method of the bar. There are some square boring bars - these should be avoided.


      • #4
        I do most of my boring using 1/2 C5 carbide boring bars that come in a set of nine. The same that are used in boring heads. Their base is round so to hold them I make a holder by placing 2" lenght of 3/4 sq. hot rolled in the tool holder. Place a 1/2" drill bit in the lathe chuck and drill a hole the length of the sq. stock. I use the tail stock to help push the carriage when the hole is drilled. Saw a slot parallel the hole so when the holder bolts are tightened, the block pinches and holds the bar in perfect position. The bars are cheap and easy to sharpen when needed.


        • #5
          Thanks for the replies, I like your idea gerry, sounds like the most inexpensive
          way to go. Thanks again !!!!!


          • #6
            BL1 and BL2 boring bars from APT are just the cats meow for all boring over .700 diameter. I have two sets of these. They take TYPG or TPU 222 or 221 inserts, are pre- "flatted" for the rakes for boring, and fit in 1/2 and over tool posts.

            The inserts are cheap, the bars sturdy, and they flat a hole bottom toot sweet, and reach from 2" to 3 1/2 inch depth.

            They are also cheap at about $25.00 to $35.00 each.

            Absolute student proof, they have survived five years of abuse with the newbies thus far, so good in fact I ordered a third set.

            Not an APT or MSC salesman, but availale thru MSC.
            CCBW, MAH


            • #7
              Second idea - Use a two flute end mill as a boring bar. It can be done, and I do this on a regular basis. The trick is this. set the end mill about .010 above center, the tooth sitting about 6 to 10 degree negative rake (turning set up, the tooth pointed down to the center). The hole must be about .010 over the end mill size.

              I bore small holes this way commonly. Had to do a 3/16 bore hole last week. Drilled it to .175, used a .125 two flute end mill, relieved at the back.

              This is the best use for those end mills that you chip off heavy one tooth with, and hate to toss it out. Use the good tooth as a boring bar. The old timers grind the mashed tooth off.

              For your hole, a 3/4 to 7/8 end mill with a smaller shank would do the job, though hung out there a bit. Use a good stone and put a .005 to .010 Nose rad on one of the teeth.
              CCBW, MAH


              • #8
                Thanks spope14,, cool idea....