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AArrggg! Turning Problem?

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  • AArrggg! Turning Problem?

    I am turning 4130 chrome Molly at about 1/2" diameter and three to 5 inches in length. I'm using a braised on carbide tool bit. It starts to cut just fine that after a couple of passes in the middle of the cut it will start to cut real shiny and a ringing sound starts. It's like it's not cutting just burnishing metal. I'm not using a coolant. what's going on?

  • #2
    What's your speed and cut?


    • #3
      What state is the 4130 in? Annealed, as rolled or hard?

      I was cutting anealed 4140 for a friend a while ago, HSS at about 2/3 the speed I'd use on mild steel did fine but I had to sharpen often.

      If it's hard, get an inserted tool holder. I bought a 1" shank MCLN tool holder after asking about cutting axles shafts in the hard state. Works great. Should also work on hard 4130 - depending on exactly how hard it is...


      • #4
        Thanks for the replies gentlemen. I was going to get more detailed, but my wife had been yelling at me to get ready for dinner we were going out and I want to get this on the net before I left. Dave, I am turning at 600 rpm and the cutting speed is real slow. I should calculate the cuttings Speed exactly but I'm in the ballpark and then a little slower. The 4130 is in an annealed condition. It almost seems like the carbide loses its cutting edge or doesn't want to dig in and cut the metal. Is that metal getting too hot and work hardening? I have a bunch of HSS, with this do a better job? Obviously it will be slower. I have provisions to mount a cooling system on my lathe, but it's in a box in parts.


        • #5
          Sounds like you might need a follower rest as the tool is rubbing (not cutting) in the middle of the cut.
          Barry Milton


          • #6
            That's what I was trying to say, the tool bit is rubbing, not cutting. I thought maybe it was deflecting also but it's hard for me to imagine that a half-inch around by 3 1/4 inches long rod with the end in a ball bearing tailstock would deflect at all, but then I am just a novice and you guys are the experts. Thanks again


            • #7
              I think you're running way to slow for carbide, even cemented. At least double your RPM. You want the chips comming off carbide at least blue if not glowing red. If you can do it without deflection increase your depth of cut as well or at least avoid taking light cuts. You don't mention what the shape of your bit is. Too large a radius will work against you since it discourages penitration of the tool. Likewise too much of a lead angle.

              If you suspect the workpiece has hardend switch to a sharp cornered bit, set over around 10* and a .010" depth of cut to get under the hardend layer. Continue with this bit until you are ready for a preliminary final cut. Then switch to a bit with a moderate radius for the last couple clean up passes.

              YMMV, try a test piece first and experiment, these are just suggested starting points.



              • #8
                Oh forgot to mention: check to make sure your bit is on the center line and is not deflecting.


                • #9
                  Sounds like the part is deflecting and riding above the tool.You might be better off with hss toolbit(hss takes less pressure to cut) sharpend with a small nose radius.
                  ...the order of bringing about change
                  is the four boxes:


                  • #10
                    a sharp tool, 1000 rpm+ .004-.006 feed+ or more and it should cut fine.

                    at work i never run feed under .010 unless its hard and I need ceramic, or I want to burnish plasic or bronze.(and i dont)

                    small parts cut at high rpm.

                    [This message has been edited by tattoomike68 (edited 03-19-2005).]


                    • #11

                      Just a thought…

                      I’d check the cutting tool’s edge under a magnifying loupe (10x or so). You can learn a lot from that. When I have symptoms like you stated I often find that the “cuttingâ€‌ edge is back a little because I rounded the cutting edge when sharpening it. If taking a deep cut with carbide it won’t seem a problem but if taking “lightâ€‌ cuts it will show the “rubbingâ€‌ effect as you stated.


                      [This message has been edited by Mike Burdick (edited 03-20-2005).]


                      • #12
                        I can add from recent experience that it could also be the quality of the carbide you are using. Some of the cheaper stuff doesn't stay sharp as long as good HSS. I recently bought a boring bar set that absolute junk. It would only cut about two passes in a 1"ID X 1 1/2" deep bore at .025 DOC and it was worn off round. Was very nice to sharpen on a cheap regular grinding stone however I'm not sure but I think I could have sharpened it on one of my wifes ginger snap cookies BTW...the new set they sent me is far better!
                        I have tools I don't even know I own...


                        • #13
                          I have never in my life had any luck with brazed carbide. Go with any of the major insert cutters. I think the braze process has some effect on the carbide and makes it in to junk.


                          • #14
                            i agree with most, use HSS,TC does work well
                            on small cuts specialy on small diameters,ok for bigger stuff.stick with HSS and make sure the tool isnt above centre hight


                            • #15
                              <font face="Verdana, Arial" size="2">Originally posted by torker:
                              I'm not sure but I think I could have sharpened it on one of my wifes ginger snap cookies
                              Oh dear, Russ. It will be no more cookies for you if your wife gets to read this.

                              Jim. Probably a bit obvious, but have you checked the tool height?