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Parting tool advise

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  • Parting tool advise

    My parting tool seems to scrape the metal out. I've never once been able to get a nice spiral of swarf and 10 times out of 10, the tool gets sucked into the work and jams.

    Speed is backgeared low (both on steel and aluminum) and parting tool is set in lantern holder with tip barely above centerline. Advance is very slow with only a few thousandths per cut. I threw the tool on the grinder to make sure the point was sharp, but still get the same results.

    Any tips or advise is appreciated. Otherwise, I'll probably keep hacksawing and facing as a work around.

    Thanks, Derek

  • #2
    Parting is a headache for many people and once was for me as well. By doing a lot of reading and experimenting for myself I learned a few things.

    1) Rigidity is the most important thing. With a lantern tool post obtaining the required rigidity may mean not using the rocker. I made a solid ring exactly the right height to put the tip of the parting tool exactly on center. Later, after purchasing a quick change tool post I found that parting became even easier due to increased rigidity and the ability to adjust tool height easily.

    2) Rigidity again; be sure your gibs are adjusted properly, even to the firm side of tight.

    3) Put the tip of the parting blade exactly on center and exactly perpendicular to the work. I carefully place a straight edge (usually a square tool bit) between the parting blade and the chuck face to assure alignment. You may have to experiment with back rake. I've been successful with zero back rake and with the slight back rake imparted by my QC tool post.

    4) Use plenty of cutting oil/fluid depending on material being parted.

    5) Be certain the tool is not only sharp but has adequate end clearance so it doesn't rub on the work. Adequate end clearance is essential!

    6) Part as close to the chuck jaws as possible and never part between centers.

    7) Sometimes more feed is better than not enough. Too little and the tool just rubs and dulls, too much and it will grab. You should be able to "feel" the proper feed as you hand feed inward.

    8) Use as narrow a parting blade as you can find.

    9) Originally I was using back gears as you are but eventually I found that I can part at speeds approaching the same speeds used for turning. The tools I am using are standard HSS parting blades.

    I don't think I missed anything but if I did no doubt someone will jump in with further assistance.
    There is a good 3 part presentation on parting by Tubalcain on youtube.
    You might want to check that out.

    Eventually you'll be able to judge infeed enough and become confident enough to let the machine perform automatic feed for you, if your machine has that capability. The positive of this is a continuous rate of feed and will produce nice curls.

    If you do a search of the HSM site you will find suggestions from several others who have mastered the science of parting. Even the accomplished probably occasionally break a blade though.
    Last edited by firbikrhd1; 05-04-2012, 02:40 PM.


    • #3
      I bought a kennametal parting set and have never had any trouble parting off since.You can buy them used even or new on ebay quite cheaply. I agree with the sentiment of having everything tightened up sounds as if the height is not correct are you sure you got the height spot on.?Alistair
      Please excuse my typing as I have a form of parkinsons disease


      • #4
        Not to demean the importance of a sharp tool but I find that the difference between using enough cutting oil and not enough is unreal.


        • #5
          Setting the parting tool above centerline is a recipe for jamming up like you described. Set it exactly at centerline, and make sure it is as perpendicular to the work as possible. I like to set the angle by pressing the length of the blade across the face of a newly-faced piece in the chuck.


          • #6
            I agree with Alistair, if you are going to get just one carbide tool, make it a cutoff tool.

            Yes, you can learn how to do it with a HSS steel one but for me it was always a white knuckle experience, along with some of my most memorable lathe crashes. The carbide based tools just work way better.

            There's a lot of different ones out there, mine uses the GTN type inserts and works well. Once secret with the carbide ones is don't be shy with them, crank up the RPM and don't be gentle with the feed.

            Paul T.


            • #7
              if the tool is barely above centerline (how much?), thats the reason it gets sucked in. lock the carriage and the top slide. tighten the cross slide gibs. also tighten the chuck well, so the work doesnt slipp. get a spay can of cutting lube, so you can get it into tho grove. use the same speed as for cutting.

              i part off with a 5 mm brazed cabide blade on my little 3 in 1 with no sweat.

              side clearance is essential, when parting, and its hard to get it with hss. exept iffanger, i think i posted pictures before.

              anyway, here it is:


              i also grind the tool left or right, depending which part is supposed to be without a burr.
              Last edited by dian; 05-04-2012, 03:27 PM.


              • #8
                Turn it up side down and run in reverse OR in a rear toolpost run forward. That way it cannot dig in.

                Yes, cutting oil is good.

                " you not think you have enough machines?"


                • #9
                  Thank you all

                  Well, great info as always. I am basically doing everything wrong (except asking the right people for help). Will try a new more rigid setup with blade properly positioned and speed adjusted up a bit.

                  Thanks again.


                  • #10
                    david, i have doubts on the rigidity of your settup.
                    Last edited by dian; 05-04-2012, 03:50 PM.


                    • #11
                      I keep the speed down because I don't want oil flung all over the shop. I use lots of oil when parting. I use some HSS parting bits I got from McMaster that have a t-shaped cross-section, so there's some side clearance. I like it as sharp as I can get it and ground with some clearance on the front, and nothing but the rake imparted by the bit holder.

                      I recently turned some 1018, and parting that off was challenging because of the variable hardness and gumminess, but I managed to get through it. Everything else, from stainless to aluminum and even Delrin is easy enough that it's almost fun.


                      • #12
                        Derek, Sawing and facing is not a work around it is the better way to go. However sometimes parting is necessary.
                        For parting forget the lantern style holder and make your self a dedicated tooling block to hold a cutoff blade. One step better would be to make a tooling block that also replaces the compound.

                        This shows both the compound replacement block and a rear-mounted block with QCTP with an upside down parting blade. That is a subject that is guaranteed to start a lively discussion. The upside down rear mounted parting tool is a good way to go if the chuck unscrewing when running in reverse can be dealt with.

                        I am not recommending the use of a QCTP in the manner shown. I have run it a little without incident but not enough to recommend it.

                        A couple of things that I have recently learned.
                        1. Setting the blade perpendicular to the axis is more critical as the depth increases. Someone recommended using an indicator, I tried it and found that just squareing the blade with the chuck was not as good.
                        2. I had a couple of old brazed carbide tipped cutoff blades that had never been used. They worked much better than I expected. They are easy to sharpen with a diamond wheel on the tool grinder with the table set to 7°
                        Byron Boucher
                        Burnet, TX


                        • #13
                          Originally posted by dian
                          david, i have doubts on the rigidity of your settup.
                          Dian, you are completely correct, it is not rigid at all. It is up side down so there is no inclination to dig in.

                          Try it
                          " you not think you have enough machines?"


                          • #14
                            Originally posted by catman81056
                            Not to demean the importance of a sharp tool but I find that the difference between using enough cutting oil and not enough is unreal.

                            I really must stress this, I get a very noticeable difference in how my parting tool cuts within 5 seconds of the last drip of cutting fluid. I feed with one hand and apply 1 drop of cutting oil every 2~3 seconds with a hand oiler.

                            Also, You may need to feed more to stop getting powder and actualy get chips. Note that once you do get chips and feed for awhile, try stop feeding and note how long it takes the tool to stop cutting. That shows you how much spring there is in the set up.

                            Oh, Btw, Do not part more then a diameter or two away from the chuck. Also its best not to part over about 1.5" or so.
                            Last edited by Black_Moons; 05-04-2012, 07:20 PM.
                            Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.


                            • #15
                              Try it on a piece of brass to get the feel of how fast to feed in. You don't
                              want to use any fluid on brass and the chips just fall out so it's easy to
                              see what is going on. Then do some aluminum with kerosene (or the infamous wd whatever). :-) work up to steel. :-)