Crashed&trashed ANOTHER cut-off tool

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  • radkins
    Senior Member
    • Sep 2008
    • 2810

    Crashed&trashed ANOTHER cut-off tool

    Well the title says it this makes the third one (HSS blades) and I have no idea what I'm doing wrong but then I have had no instruction on how to use one either, what little I know about machining has been self taught in my small shop with no one else around so please bear with me. I have made sure the tool was centered with the work (is that right?), I have tried various speeds, been careful to feed straight in and I take my time and feed very lightly but still I just can't seem to get it. I have broken several blades but again this time I have managed to trash the third blade and holder both at the same time, fortunately these are just relatively cheap tools from Grizzly. Any suggestions?
  • plunger
    Senior Member
    • Nov 2006
    • 2633

    #2
    Try it upside down. I find if I cut the groove wider than the blade it helps with a bit cause it allows the chips to escape.I k*k myself when it comes to parting and I am always scared I am going to crack my toolpost in a worse case scenario so I set my lathe on its highest gear speed but drop my vfd speed right down. My machine will stall in a jam rather than break the tool.I think some guys set the tool slightly lower than center so if it jams it tends to not dig but I am not sure of this and dont do it myself.I also dont use my parting tool upside down but I hear its more rigid this way and the swarf also falls out with gravity.

    Comment

    • iMisspell
      Senior Member
      • Feb 2013
      • 546

      #3
      Just some tidbits...

      Making sure cutt-off blade is parallel to chuck face.
      Have blade as short as possible.
      Having the tip a hair (really just a hair) below center.
      Use oil.

      Posting back more details about what whent on when you broke the blades might help others respond.
      Material being cut, diameter of stock, spindle speed, feed by hand or under power, type of HSS cutoff blade, the size of the blade (width), the size of your machine, was it sqilling while cutting, chattering while cutting - any little detail can help.
      ~ What was once an Opinion, became a Fact, to be later proven Wrong ~
      http://site.thisisjusthowidoit.com
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      Comment

      • goose
        Senior Member
        • Jul 2007
        • 837

        #4
        Cutting off with HSS blades is hit and miss. Just a matter of time before the next blade explodes and sends fragments all over the shop.
        You're asking a thin (often 3/32"s) piece of a brittle material to withstand tremendous forces in a narrow, deep cut.
        Switch to carbide. There are many options out there, if on a budget check ebay for some tooling to start up with. Despite the initial costs, the inserts last a long time and you'll end up saving in the long run with less tooling loss and saved time.

        Occasionally I've had a crash with carbide, but it's my fault for pushing the operation under power feed.
        Gary


        Appearance is Everything...

        Comment

        • A.K. Boomer
          Senior Member
          • May 2006
          • 20865

          #5
          What kind of material are you parting off? is it aluminum? could it be balling up and "welding" itself to the cutter?

          Comment

          • radkins
            Senior Member
            • Sep 2008
            • 2810

            #6
            Originally posted by iMisspell View Post
            Just some tidbits...

            Making sure cutt-off blade is parallel to chuck face.
            Have blade as short as possible.
            Having the tip a hair (really just a hair) below center.
            Use oil.

            Posting back more details about what whent on when you broke the blades might help others respond.
            Material being cut, diameter of stock, spindle speed, feed by hand or under power, type of HSS cutoff blade, the size of the blade (width), the size of your machine, was it sqilling while cutting, chattering while cutting - any little detail can help.
            Ok I knew about keeping parallel to the chuck face, that's what I meant when I said I feed straight in and also I understand about what happens if a tool digs in running above the center line. Once I tried running well below the centerline and that one resulted in instant disaster. What you mention that I have not been doing is the oil, obvious as it seems now that you mention it I had not even thought of that!

            The material this last time was 1 1/4" OD x 3/16" wall 4130 seamless tube with barely enough blade sticking out to do the job but I have had serious problems even with 1018, I tried this one at 90 RPM and was feeding manually at a very light loading but while at first it seemed to be working just fine (no squealing or chatter) without warning it seemed to snag and not only broke the blade (3/32") but bent the tool itself. The tool was sharp and had the proper reliefs on the cutting tip and the sides but as I already mentioned I was cutting dry, as soon as I get another tool/blade I will try again but this time with cutting oil.

            Is thread cutting oil a good choice? I have a coolant system on my lathe and I normally use that but at such a low RPM and light cut I didn't think it necessary so I left the cut dry in order to better see what was happening, maybe that contributed to what I ultimately did see!


            goose, since I will be needing a new tool and that broken blade was my "spare" I will buy a carbide setup this time, I was already considering that but figured I would try to work out the procedure with the cheaper tool first.

            Comment

            • PixMan
              Senior Member
              • Sep 2009
              • 2077

              #7
              What kind of holder for a cutoff blade do you have? Most holders for HSS are too small for carbide insert technology. In the world of quick change tool posts, it's the No.71 or Dorian 7-71 holders which can take the 1" or 1-1/4" (26 or 32mm) blades.

              The difference in cutting off with good insert technology vs. futzing around trying to make HSS work right is like day and night.

              Comment

              • radkins
                Senior Member
                • Sep 2008
                • 2810

                #8
                That 1-1/4" was a typo, it was 2-1/4" tube.

                Comment

                • A.K. Boomer
                  Senior Member
                  • May 2006
                  • 20865

                  #9
                  when it crashes is there evidence that the cutter has broken through the tubing on one side?

                  tubing can add some complexities --- if the cutter is not sharp or for some reason not hitting right and it's taking a fair amount of pressure to cut then when it finally does break through it can have some detrimental effects...

                  Comment

                  • firbikrhd1
                    Senior Member
                    • Mar 2001
                    • 1610

                    #10
                    Like you, I am self taught and make no claim to be an expert, but I know what has worked for me. Following are 4 links to threads similar to yours and to which I and others have interjected their experiences and thoughts on the subject. The advice given in these links by others as well as myself might help you resolve your parting issues. Read the posts carefully and follow them to the letter and I'll bet your parting issues will go away, unless your machine has some issues with having so much clearance in ways and bearings that no semblance of rigidity can be obtained.
                    Here are the links:






                    Comment

                    • oxford
                      Senior Member
                      • Jun 2011
                      • 2769

                      #11
                      I noticed on my tool holder that a "t" shaped blade does not sit flat against the side of the holder. I need to keep a piece of shim stock on the side of the blade.

                      Comment

                      • Rosco-P
                        Senior Member
                        • Mar 2012
                        • 3033

                        #12
                        Originally posted by oxford View Post
                        I noticed on my tool holder that a "t" shaped blade does not sit flat against the side of the holder. I need to keep a piece of shim stock on the side of the blade.
                        It's been posted before... Some of the import cutoff toolholders don't have a recess for the "T" portion, mill a recess for it, so the side of the blade is completly supported.

                        Comment

                        • Bob Ford
                          Senior Member
                          • Dec 2006
                          • 1140

                          #13
                          Radkins,

                          If you are using H2970 Make sure that back rake is no more than 5°. You may have to make a washer to go under the tool holder ring. Too much back rake causes the tool to dig in. I run the lathe at normal speed for the material and size, lots of cutting oil. Cutting oil is more for lubing the sides of a cutoff tool. Very little overhang. In cutting large tube you may need a steady rest between chuck and parting tool. Be very careful about penetrating a tube on one side Instant disaster. The tool tip needs to be ground parallel with the work. After a cut look with a glass at the corners of the tool for wear, regrind if needed.

                          Bob

                          Comment

                          • J Tiers
                            Senior Member
                            • Jan 2004
                            • 44281

                            #14
                            Originally posted by goose View Post
                            Cutting off with HSS blades is hit and miss. Just a matter of time before the next blade explodes and sends fragments all over the shop.
                            You're asking a thin (often 3/32"s) piece of a brittle material to withstand tremendous forces in a narrow, deep cut.
                            Switch to carbide. There are many options out there, if on a budget check ebay for some tooling to start up with. Despite the initial costs, the inserts last a long time and you'll end up saving in the long run with less tooling loss and saved time.

                            Occasionally I've had a crash with carbide, but it's my fault for pushing the operation under power feed.
                            ????????????????

                            Not true in my experience. Parting off has become pretty routine, using whatever tool looks like it will work. Thin (1/16") ground-from-regular -toolblank, thicker type also ground from a toolblank, sometimes even an insert carbide tool. Once in a while I have actually used a regular HSS cutoff tool.

                            HSS is not brittle and troublesome. SETUPS are brittle and troublesome.

                            1) get the tool parallel with the feed. Using the front of the chuck as a reference is good (unless you are using collets)

                            2) make a reasonable effort to be on-center. With a hollow form it's not crazy important, but with solid it keeps the little tit left in the center from being large.

                            3) watch the feed. Sometimes a slow feed is best, sometimes a faster one.

                            4) Watch out for "wind-up".... if you feed with high pressure, you can get a dig-in when something changes and the tool suddenly can cut freely.... That can easily happen when you break through when cutting tubing, especially if the tubing is not on-center, since there will be a thicker wall on one portion than the rest. if you break through in one area, there may be a substantial part left on the opposite "side", which can catch and break things. Feeding easy will keep that down, so long as the work is centered.

                            5) cutting oil will usually help

                            6) Sometimes it's good to cut in partway, then back out, move over a bit and cut again. That relieves the drag of the blade on part of the cut.

                            7) A tool that is relieved below the edge is good, as it drags less. most HSS cutoff blades are like that.

                            8) A tool with a wider cutting end than body is also good, as it will drag ONLY at the cutting edge, and is clear of the cut everywhere else. That is one thing that carbide inserts DO have going for them, and HSS normally does not.

                            9) machine should be tight. Loose machines will have more "wind-up" and cause much more chatter, besides having "dig-ins" and catching on the sides of the cut more..

                            There are more factors as well
                            CNC machines only go through the motions.

                            Ideas expressed may be mine, or from anyone else in the universe.
                            Not responsible for clerical errors. Or those made by lay people either.
                            Number formats and units may be chosen at random depending on what day it is.
                            I reserve the right to use a number system with any integer base without prior notice.
                            Generalizations are understood to be "often" true, but not true in every case.

                            Comment

                            • goose
                              Senior Member
                              • Jul 2007
                              • 837

                              #15
                              Originally posted by J Tiers View Post
                              ????????????????

                              Not true in my experience. Parting off has become pretty routine, using whatever tool looks like it will work. Thin (1/16") ground-from-regular -toolblank, thicker type also ground from a toolblank, sometimes even an insert carbide tool. Once in a while I have actually used a regular HSS cutoff tool.

                              HSS is not brittle and troublesome. SETUPS are brittle and troublesome.

                              There are more factors as a well
                              I beg to differ. My experience is that an operation that had taken minutes is now seconds. There is no need to keep it tight, watch the feed, use oil, etc. Just mount the carbide tooling and go.

                              I probably save more time in a typical cutoff OP by not grinding alone than in the past, before even getting to mounting the HSS on the toolpost I'd be done with carbide!
                              Gary


                              Appearance is Everything...

                              Comment

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