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TCGT VS. Vertical Shear Bit...Who Will Win?

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  • #16
    Originally posted by Willy View Post
    Just a simple back to back test of both under less than ideal conditions for both.
    I have a hard time understanding the purpose of this test.
    Last edited by MichaelP; 10-15-2021, 05:42 PM.
    Mike
    WI/IL border, USA

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    • #17
      I use inserts for aluminium frequently, TCGT, VCGT, VMNG, TNMG, WNMG, and they all work very well, even the negative type that some people think cannot possibly work with polished sharp inserts. I needed a good finish in a bore with a medium soft steel and used aluminium grade H01 insert and the bore was excellent, and the insert was still undamaged, surprising since I was boring soft jaws with it.

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      • #18
        As pictured, I'd say that the shear bit looks better
        That said, the slightest touch with some scotchbrite on the xxGT side gets rid of the fuzziest and produces a nearly identical finish. I use DCGT inserts near exclusively in my lathe, in both steel and aluminium. They don't hold up as well as steel-specific inserts, but I've found you can run act like they're HSS and get excellent results with them

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        • #19
          Originally posted by MattiJ View Post

          In my experience Carbide seem to hold up for a loong time at slow speeds and very small DOC.(talking about these sharp xxGT inserts)

          and these aluminum specific inserts are probably ”straight” tungsten carbide that is ill-suited for heavy&hot cuts in ferrous materials. Run them in hss speeds in ferrous materials and they last pretty well.
          Not in mine. Chip weld is a big problem at too low a speed. I have a feeling our "long time" is probably on a pretty different scale, I am going to guess you mostly work on little stuff with short cuts. A "long time" at low speed does not cover much linear distance. A long time at high speed covers quite a lot of linear distance.

          At such a light depth of cut the inserts should hold up just fine at high speed. I think the actual speed doesn't matter much to the insert - it's the heat produced that is the problem. It's difficult to make generalizations though, there are too many variables to do so.
          Last edited by eKretz; 10-15-2021, 05:02 PM.

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          • #20
            Originally posted by MichaelP View Post
            I have a hard time to understand the purpose of this test.
            As I mentioned previously. Not intended to be an all inclusive or thorough evaluation, simply meant to demonstrate options. Perhaps I should have used a more appropriate title however it is now cast in stone.
            However an excellent point on running carbide as if it were HSS or worse yet the opposite!

            This was a completely last minute effort before winding down the shop the other day and thought it might provoke some thought on getting those that have difficulty obtaining a decent finish on gummy material to try something different.
            Home, down in the valley behind the Red Angus
            Bad Decisions Make Good Stories​

            Location: British Columbia

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            • #21
              to be honest, I've found TCGT/CCGT inserts to give a very smooth but not shiny finish in steel. Kind of a dull matte colour like you showed. CCMT gives a nice shiny (burnished?) finish if you give it sufficient DOC. For both I'd be running at least twice as fast as that.

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              • #22
                What lathe did you use? That can make a significant difference in finish. What about nose radius of the tools?

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                • #23
                  that to me or to Willy?

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                  • #24
                    What are you really testing if neither were ran at their optimal settings, especially the carbide? My vote would be to use a better alloy steel, or run faster with the carbide.

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                    • #25
                      Originally posted by eKretz View Post

                      Not in mine. Chip weld is a big problem at too low a speed. I have a feeling our "long time" is probably on a pretty different scale, I am going to guess you mostly work on little stuff with short cuts. A "long time" at low speed does not cover much linear distance. A long time at high speed covers quite a lot of linear distance.

                      ..................
                      I've run long cuts and many of them one after another using carbide at what one could call HSS speed. And that in 4140PH, making horizontal mill arbors. Lots of passes one after another, and a long time per pass. Never had any particular problem of chip welding on carbide, whether brazed or insert.
                      2730

                      Keep eye on ball.
                      Hashim Khan

                      Everything not impossible is compulsory

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                      • #26
                        Originally posted by J Tiers View Post

                        I've run long cuts and many of them one after another using carbide at what one could call HSS speed. And that in 4140PH, making horizontal mill arbors. Lots of passes one after another, and a long time per pass. Never had any particular problem of chip welding on carbide, whether brazed or insert.
                        Harder steel is actually less likely to cause the problem in my experience. It's the gummy stuff that is troublesome. Using cutting oil or coolant can also help. The problem is real, believe you me.

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                        • #27
                          Originally posted by eKretz View Post

                          Harder steel is actually less likely to cause the problem in my experience. It's the gummy stuff that is troublesome. Using cutting oil or coolant can also help. The problem is real, believe you me.
                          I've seen a heck of a lot more built-up-edge problem with HSS than carbide. I've also run a good bit of long sessions cutting 1018 and had the same thing..... no particular problem. HSS seems much worse for BUE than carbide.

                          I know the problem is real, but it does not seem worse with carbide. It seems like less of a problem with carbide.
                          2730

                          Keep eye on ball.
                          Hashim Khan

                          Everything not impossible is compulsory

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                          • #28
                            Originally posted by J Tiers View Post

                            I've seen a heck of a lot more built-up-edge problem with HSS than carbide. I've also run a good bit of long sessions cutting 1018 and had the same thing..... no particular problem. HSS seems much worse for BUE than carbide.

                            I know the problem is real, but it does not seem worse with carbide. It seems like less of a problem with carbide.
                            For me it has always been worse with carbide at improper speed. HSS gets a little BUE but generally doesn't get damaged as badly in my experience when it's removed. The carbide fractures when the BUE comes loose and there goes size on your finish cut.

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                            • #29
                              I mostly run lathes for a living, some are small and some not so small.

                              The only useful advice that I can give when using a lathe is to choose a Surface Speed and stick to it, this is of course not possible.

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                              • #30
                                Originally posted by Willy View Post
                                Found a piece of gummy 1 1/2" hot rolled bar that I had use a part of last year. At the time I had just used a known sharp HSS tool bit to obtain a pretty decent finish considering how sticky and gummy this bar seemed to be. You can see the old turned finish which is yellowed from from time and some rust preventative I sprayed on it at the time.

                                So fast forward to the other day when I had this same piece chucked in the lathe and thought it might be interesting to see the difference between a new TCGT insert meant for aluminum, although they work great for a finish passes on gummy material due to it's geometry, and a HSS vertical shear bit I'd used in the past.

                                I think the turning speed was about 350 rpm, the depth of cut was .002" and I used a feed rate of .003", cutting dry for both. The photo shows the TCGT side to the right near the live center and the portion turned with the vertical shear bit is to it's left.
                                I'm sure I could have tweaked both of these cuts a bit but just wanted to do a quick back to back pass with all else the same except for the tooling. The cuts have not been dusted off with a rag or brush, they are as-cut.



                                Reason for edit: spelling
                                Yeah, I didnt read all the goodies, you are too smart for me. So? My Take

                                I like cintered carbide. I use mostly. I have HSS and all types of "blanks". I like the carbide insertys for my uses. Which is slow speed. Yup, carbide works with slow speed folks...

                                350rpm may sound slow. What about the diameter?? Hmmhmm. SFPM.

                                No, kidding. I dont pull metal off that fast. I am happy peeling .001" off at a time.. JR

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