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  • Boring head chatter

    I made a couple of boring bars for my 75mm boring head and I tried them out. I get chronic chatter when i use them. I am using positive carbide inserts. Only when I take bigger cuts larger that 0.5mm does the chatter stop. But the finish is not good very rough.

    When I use the tools in my lathe for boring they work beautifully with really good finishes and no chatter at all.

    Is there a special way boring head cutters should look or should I just be using HSS for this type of work???????????
    Precision takes time.

  • #2
    What material are you trying to cut? I assume that you are having the problem when you are boring in a mill. Your speed may be to fast. The boring head will be out of balance once you make any adjustment to it. Try to reduce your speed and see what happens. I am in the slowest speed on my mill when I am boring a hole.

    Joe

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    • #3
      Ringer,
      Are you using the boring head for facing duties?. If so I suspect the chatter could be from the cutter face having too much contact area. If you look at facing bars the cutter face is at less than 90deg to the horizontal something like 87deg or less. Auto feed on the boring / facing head is a great help (also expensive), keep the bar protrusion from the head face to the minimum possible.

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      • #4
        I am using it to bore out some test holes on mild black steel, hole size approx 35mm. I am spinning it at around 325 rpm the next higher speed is 600 rpm and is too fast. The bar protusion from the head is approx 60mm and the boring bar is 19mm diameter.
        Precision takes time.

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        • #5
          Last time I bored a hole in mild steel, I believe I was running around 100 RPM. That was with a sharp cemented-carbide bar in a 3" boring head.

          It strikes me that the carbide insert will want to see higher RPM and/or deeper cuts to be effective, but I'd also wager your setup isn't rigid enough (either the mill or the borinhg head or both) for that kind of speed.

          Try the same depth of cut but half the RPM. That's a guess on my part, but it's what I'd try first. Also, if you're using the power downfeed, you might try a smaller cut-per-pass setting.

          Doc.
          Doc's Machine. (Probably not what you expect.)

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          • #6
            You are right Doc, I just went out and tries it with slower speeds and the chatter disappered but the finish was not good as I know carbide likes fast speeds.

            For similar sized holes when boring in the lathe i usually run at 800rpm with good results. I was thinking similar speeds in the mill would work. How wrong i was.....

            I've got a brazed carbide cutter somewhere that fits in the boring head I will sharpen it up to a sharp point and see if i get a better finish..

            Thanks everyone...
            Precision takes time.

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            • #7
              Here's a few thoughts, which may or may not help:

              A boring head is not a particularly rigid setup. What kind of shank is on it? If it's a straight shank in a collet, you might want to think about getting a taper shank to match your mill's taper. When I got a boring head, I first tried a straight shank in a collet and found it wasn't solid enough.

              Play around with the cutting angle (turn the boring bar in the boring head slightly) and see what happens.

              Slower speed...already mentioned.

              Light cuts...to go along with the lack of rigidity.


              ----------
              Try to make a living, not a killing. -- Utah Phillips
              Don't believe everything you know. -- Bumper sticker
              Everybody is ignorant, only on different subjects. -- Will Rogers
              There are lots of people who mistake their imagination for their memory. - Josh Billings
              Law of Logical Argument - Anything is possible if you don't know what you are talking about.
              Don't own anything you have to feed or paint. - Hood River Blackie

              Comment


              • #8
                It takes more force for carbide to penetrate the same material as HSS. Single point boring of holes using radial adjustment in a mill with carbide might be tempting but unless the bar has a short overhang/dia, ratio chatter and finish problems always pose a hazard; particularly in small cuts where the low chipload has little damping effect on self excited mechanical oscillation (chatter). Add to this most boring tooling has excessive clearance and built-in regenerative cutting kinematics and you wonder how carbide can be made to work at all in a radial offset boring head.

                The brightest minds in the machinist trade have grappled with this problem and to my way of thinking none have succeeded as well as the DeVlieg Microbore system. This is a boring system consisting of a series of tapered bars made integral with their shanks having tools with built in micrometer adjustments. It stands to reason that this is also the most expensive and requires the greatest assortment of hardware to make it work. We had two drawers of a Lista cabinet devoted to the necessary parts and cooling to cover the range from 3/8" to 3" in a single set of 50 MMT bars. In 1972 this set and consumable tooling cost the shop over $5000.

                If I have a deep bore to make, I regard single point carbide as almost a lost cause unless the material is so hard or abrasive as to preclude HSS.

                G&L's Clarke tooling system is a much better solution for uninturrupted deep holes. Here the bore is rough drilled, semi-finished with a stub bar to locate the axis in the work, and finished with a floating double cutter whose diameter can be set directly with a micrometer. This radial float ensures equal stock removal and greatly reduces the need for ultimate rigidity in the bar. I've bored 1 1/2" holes 20" deep in cast steel to a square shoulder and gotten a consistant size and finish requireing only a brush hone to make it suitable for a Disegrin lip seal. This is also expensive tooling made only in shanks suited for HBM's and larger machine tools but the principles are adaptable for the small mill and carbide works very well with it.

                I strongly suggest you with small milling machines think critically before using carbide as the first option in precision single point boring out of radial offset heads. Carbide is great where it's suited but it requires exceptional rigidity to achieve accurate size holding and good finishes at the cutting speeds necessary to make them work.

                Conventional boring head are a compromise in rigidity at best but they are both ubiquitous and very convenient. For that reason make sure your selection of HSS boring tools is equal to or superior to your selection of carbide. You will use them more and usually get better, and in the end, more economical results.

                Many's the time I've given up on boring heads and bored from the largest practicable solid bar out of the spindle adjusting the size by bumping out the tool registering the increase in cut radius with a dial indicator.

                There used to be a large amount of unwritten lore in the art of accurately locating and boring deep holes. Much of has finally been written down in the Metals series of machine shop reference particularly the volumes regarding metal cutting. If you ever track down the work take a few evenings to read up on their discussion of boring holes.

                Spend a couple of years on a horizontal boring mill in a job shop having a rapidly evolving and diversified workload and your soon learn them all or fall by the wayside, a victim of Darwinian selection.

                Is this a great trade or what?

                [This message has been edited by Forrest Addy (edited 12-11-2004).]

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                • #9
                  Just thinking, are your x and y axis locked?

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                  • #10
                    Ringer; I agree with most of the replies.From my experience here's my 2 cents; use as short a boring bar as possible, slow down your rpm(way down)a positive rake is very important(eyeball down the boring head),take light cuts,use lots of cutting oil, of course use a sharp tool, also try HSS. Hope this helps

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                    • #11
                      All replies are great. I am printing them out as I hit boring in the mill after vacation.

                      The single bet buy I ever got anywhere was a double set of solid carbide shanked boring bars from 3/8 diameter to 1 inch diameter, all in 1/8 increments, and different lengths. 12 bars in all, 24 bars total for two sets. I have yet to change inserts in but the 3/8" and the 3/4 diameter. I use these on deep holes and in my boring head when I am out of luck in the chatter or taper department. Auction cost - $10.00 because nobody knew what they were, and I got a guy to break them out of a tooling lot for me - a big lot of tools he bought for $50.00

                      I mention this because through many vendors, you can get these relatively cheap now compared to a few years ago. I have seen some 3/8 inch soild carbide shank boring bars used in some boring heads on CNC to hold some pretty good tolerance stuff with great tool wear on the insert as a result.

                      Just a far off suggestion for a few of you.
                      CCBW, MAH

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                      • #12
                        Ringer:
                        When using boring bars in the lathe care must be taken to insure proper set up - greater care must be taken to insure proper set-up when used in a boring head.

                        The poor finish is evidence of improper clearance (rubbing) of the insert in the bore (on a larger bore this problem clears up with clearance problems). The usual solution is the use of smaller inserts for smaller bores - triangular inserts go as small as .160" i.c. for a .285" bore. What happens is when the cutting edge is set on or below the centerline of the bore the bottom edge of the insert drags on the lower wall of the bore and scars the bore - hence the poor finish. By setting the cutting edge slightly above the centerline (prefered) this can often be avoided - unless the bar/insert is sized too large for the bore. The above center setting also gives a more positive rake to the insert in relation to the materials bore.

                        Care also has to be exercised to allow chips a free path to exit over the top of the bar - if the bar is set too high in the bore chips can accumulate on "top" of the insert and also cause scarring of the bore.

                        [This message has been edited by Thrud (edited 12-11-2004).]

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                        • #13
                          Oh -- one other thing. Lock the boring head by tightening up its gib screws after you adjust it, to eliminate one more source of possible flexing.
                          ----------
                          Try to make a living, not a killing. -- Utah Phillips
                          Don't believe everything you know. -- Bumper sticker
                          Everybody is ignorant, only on different subjects. -- Will Rogers
                          There are lots of people who mistake their imagination for their memory. - Josh Billings
                          Law of Logical Argument - Anything is possible if you don't know what you are talking about.
                          Don't own anything you have to feed or paint. - Hood River Blackie

                          Comment


                          • #14
                            Well there's more info here than you can poke a stick at.

                            I made a HSS holder by drilling a 1/4 hole in a piece of 4140 and heating it red hot with the oxy and then forced a piece of 1/4 HSS through it(i rounded the end off on the gringer first). Might not be world's best practice of making a square hole but it worked.

                            Grubbed screwed a piece of HSS in it and stuck it in the boring head. Worked quite well. Could take fine cuts with no chatter. Bit of a poor finish but probably due to my quickly sharpened tool bit.

                            Tell you what the amount of information and help on this board is nothing short of amazing. Plus there doesn't seem to be plagued by the bickering i see on other forums.

                            See Ya
                            Precision takes time.

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                            • #15
                              Ringer, so you hot swaged the tool holes square in your boring bars? Didn't the hole shrink up on cooling?

                              You got me going. I have to try your trick. It sounds quicker than my SOP and some of my bars are getting ratty.

                              I've rough filed many a boring bar and hammer broached the hole with a tool I made from O/S HSS. Over theyears I've higraded one of each nominal size a few thou. O/S.

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