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Parting Off Tips Please!

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  • Parting Off Tips Please!

    I'd have to say my most hated thing to do in machining right now is to use the parting bit on a lathe. Wether for undercutting or parting off... or wahtever... i hate it... If anyone has ANY general tips at all, speed/feed wether to hand feed or power feed? etc. Anything at all that you think would help with parting!

  • #2
    I hated parting until I made a rear mounted tool post with the tool held upside down. Now I actually like parting off.


    • #3
      First use lots of cutting oil, make sure your part off tool is sharp also. I never power feed just because I like to be able to feel what it is doing. In a CNC lathe with coolant you can part off with a much faster RPM and feedrate, but on a manual just slow it down into the 100's or whatever your lathe comes close too. If parting off a particular big diameter part and wasting a little stock isnt a problem I will go part of the way in and then pull it out and move over the parting tool .050 to .075 and remove that material also, then move back to your original cut and keep parting. This helps keep the parting tool from grabbing. I have never seen a rear mounted tool post for parting but mike w seems to like it , so maybe it is something for you to look into.


      • #4
        I am trying to eliminate parting off from my life.
        I made a table, used in conjuction with a slitting saw, run between centers, with a rudimentary fence.
        Cut very straight, very smooth.
        Thinking about a new version, clamps, advance (table/work) into the blade using the cross slide


        • #5
          Depending on what type of lathe you have, you may want to try a narrower parting tool if the machine lacks power or rigidity.

          Be sure that the tool is sharp, set at the proper height and absolutely at right angles to the spindle axis. Set it for the minimum overhang for the diameter you're parting off.

          I've been using AXA and BXA quick change type cutoff holders on two different machines with good luck. For speed and feed, I generally run about 1/3 the turning speed and very slow feed (around 0.001 IPR for this chicken ). I drip small amounts of cutting fluid from a hypodermic tipped bottle right onto the tool or parting groove.

          Running the tool upside down and spindle in reverse can work well but be careful if you have a threaded on chuck. Also, the cutting force in reverse is trying to lift the carriage but I've had good results with this type of setup as well.

          If you're grinding your own bits, it helps to grind some relief on the sides to avoid any scraping of the "walls" as you go in but if you're set at exactly 90 degrees it doesn't seem like a big problem (IMHO).

          Finally, it's always a good idea to lock the carriage for parting off as ANY movement will cause scraping and jamming.



          • #6
            What size lathe? If stouter than South Bend Heavy 10 , get a carbide insert type parting blade and holder and go at it. They are amazing. You can part CRS at 250 FPM, 0.003 in/rev, no lube no problem. You'll want rigidity and horsepower.

            If using HSS blades, try the P-type; there's less drag. Never modify the top of such a blade. Any grinding on the top leaves the tip narrower than anywhere else, leading to drag and binding. With HSS, I find I can only part cast iron and brass dry. Steel needs sulfur oil and aluminum needs kerosene or WD-40. I've no doubt soluble oil mist or flood would work great.


            • #7
              If you are using HSS blades, then it is critical that the blade is at a "right angle"..Try dialing in your blade so its absolutey straight..This will keep you from snapping blades...

              Indexables are obviously the way to go, especially with the insert because the insert curls the chip which is thinner then the "kerf"...HSS blades should be ground with a positive hook on it so the chips will break or curl up into a spiral...

              I part off 5" diameter aluminum..This sucks big time cause sometimes the chips will weld itself to the blade..coolant is mandatory!!



              • #8
                I MUST power feed. the chatter and singing is caused because it wasn't feeding enough.

                It took me a while to get up the nerve but it's no big deal once you take the plunge.

                must be a somewhat ridgid setup. minimum overhang to get the thing parted, tip on center. perpindicular, carrige locked, etc...

                then, just select a feed that seems a tad to fast, (don your safety glasses) engage the feed and behold the spectacle!



                • #9
                  Something I've wondered about. I always seem to get some clatter marks on the parted face as if the blade is vibrating left and right while cutting. This has happened when cutting steel using a parting tool in a left hand holder in a lantern style post. I've tried different speeds and feeds. Always use lots of cutting fluid.

                  What I wonder is, does the bend in the tool holder contribute to the clatter? Is the bend in the holder causing it to twist? Would I be beter off with a straight or perhaps a right handed holder (because it would twist in the opposite direction)?

                  Paul A.
                  Paul A.

                  Make it fit.
                  You can't win and there is a penalty for trying!


                  • #10
                    Paul: The marks might be from the tool "hogging" ... where it hesitates and then grabs a deeper bite of the material. This can be caused by the backlash in the cross slide. You might try to tighten up the slide a bit to see if that has any effect. I've had a similar effect (hogging)from the tool tip not being ground quite right nor sharp enough.


                    • #11
                      My favorite parting tool is a hacksaw.
                      Free software for calculating bolt circles and similar: Click Here


                      • #12
                        Do you use a lantern style toolpost on your SB? Armstrong style parting tools? How do they work out ... or is the hacksaw the answer


                        • #13
                          I still use the lantern style tool holder. There aren't very many times that I find the need to actually use a parting tool in the lathe. It is much easier and less problem to cut either with a hack saw or in the bandsaw. I avoid using a parting tool as it probably is responsible for more machine crashes than any other operation. On a large heavy rigid machine it is a different story but on a lightweight like my SB9 I avoid doing stuff that will possibly damage it.
                          Free software for calculating bolt circles and similar: Click Here


                          • #14
                            Putting the blade upside down makes a world of difference.The hss blades even work good that way.But once I used the carbide the first time I was hooked.You can get them down to 1/16 wide,if your machine can't handle that,then you need a metal lathe and not a wood lathe.
                            I just need one more tool,just one!


                            • #15
                              For parting nothing beats an Iscar Self -grip parting tool with the GFN inserts.Use the IC328 grade.You will feel like Moses!!
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