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

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  • #31
    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.

    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.
    I usually resort to DCGT aluminium inserts when I don't have enough rpm available, tolerances are tight and material is gummy so in a way you are right about that I never do any serious material removal with them. But the finishing insert usually last until I chip it accidentally (yes, clumsy bastard)

    In my experience carbide grade used for example on alumnium specific Korloy H01 is totally hopeless at high speeds in steel but holds up nicely at HSS speeds(ie straw colored chips)
    Sharp cermet insert would be better: sharp and works well on ferrous materials at high speed but DCGT cermet inserts are like 10 times more expensive than chinesium H01 DCGT.
    And they both still chip just the same..
    Location: Helsinki, Finland, Europe

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    • #32
      Shiny mild steel parts made yesterday from hex bar stock in one shot.

      Face and turn the OD on one end, spot drill then drill and ream the thru hole .328" +.005" -.000"

      The parting tool does the small diameter and large chamfer then cuts it off, the only second operation is for deburring the back side hole.

      7 minutes run time per part, CNMG inserts for the OD work at 500 SFM at .05" DOC/.015 IPR for roughing and .005" DOC/ .005 IPR for finishing.

      It worked a charm for 60 parts. This was very loud (-:

      I limited the spindle to 2000 RPM's
      Last edited by Bented; 10-16-2021, 10:43 AM.

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      • #33
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        • #34
          Willy I have a wimpy 9 inch South bend. Also use the inserts you are testing. On a similar bar of hot rolled scrapbinium I'll get a great finish by spinning it as fast as the machine will go. *Cardboard needed as a chip deflector. Give it a try and report back.

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          • #35
            Originally posted by eKretz View Post

            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.
            That's about what I figured you meant, and I have NEVER HAD that problem at "improper speeds". The speed is ALWAYS "improper" because the machine does not have the power to take big cuts at high rpm.

            The ONLY time I ever break an insert is if the machine stalls (belt slip), because it will turn a slight amount backwards after stopping. With the tool still in the cut, that sometimes breaks the insert tip, or the HSS tip, for that matter. Since going with 3 phase, that does not happen much.
            2730

            Keep eye on ball.
            Hashim Khan

            Everything not impossible is compulsory

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            • #36
              Originally posted by J Tiers View Post

              That's about what I figured you meant, and I have NEVER HAD that problem at "improper speeds". The speed is ALWAYS "improper" because the machine does not have the power to take big cuts at high rpm.

              The ONLY time I ever break an insert is if the machine stalls (belt slip), because it will turn a slight amount backwards after stopping. With the tool still in the cut, that sometimes breaks the insert tip, or the HSS tip, for that matter. Since going with 3 phase, that does not happen much.
              Lucky you. Are you a full time machinist?

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              • #37
                Originally posted by eKretz View Post

                Lucky you. Are you a full time machinist?
                God forbid!

                I do things for a few customers I know. I used to do many of my own prototypes when I was working as a designer of products, as well as some fairly simple tooling for employers, but it was not my main job.I do have a fairly well-equipped shop, and I make my own tooling, and parts etc for machinery that I refurbish and sell from time to time.
                2730

                Keep eye on ball.
                Hashim Khan

                Everything not impossible is compulsory

                Comment


                • #38
                  Originally posted by J Tiers View Post

                  God forbid!

                  I do things for a few customers I know. I used to do many of my own prototypes when I was working as a designer of products, as well as some fairly simple tooling for employers, but it was not my main job.I do have a fairly well-equipped shop, and I make my own tooling, and parts etc for machinery that I refurbish and sell from time to time.
                  I may be a little sensitive to the problem seeing as how I was full time and supervising a bunch of other guys also. It is a tough thing when you lose an edge in the middle of a 40 minute cut. Lots of time wasted. I am not full time anymore, but spent a lot of years in the biz.

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                  • #39
                    No 40 minute cuts, although plenty of 40 minutes (or more) of cutting.... not the same thing, quite, as far as having the tool get messed up in the middle.
                    2730

                    Keep eye on ball.
                    Hashim Khan

                    Everything not impossible is compulsory

                    Comment


                    • #40
                      Originally posted by eKretz View Post

                      I may be a little sensitive to the problem seeing as how I was full time and supervising a bunch of other guys also. It is a tough thing when you lose an edge in the middle of a 40 minute cut. Lots of time wasted. I am not full time anymore, but spent a lot of years in the biz.
                      Yeah there are few things that suck worse than losing it with an inch to go... got the t shirt.
                      I do mostly mechanical maintenance and fabrication , with whatever machining is necessary. Both at work and at home. Keeping the bosses machines running.
                      Last edited by nickel-city-fab; 10-17-2021, 02:32 AM.
                      25 miles north of Buffalo NY, USA

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                      • #41
                        Originally posted by eKretz View Post

                        I may be a little sensitive to the problem seeing as how I was full time and supervising a bunch of other guys also. .
                        Yeah? I have seen this in only two jobs of mine. I had so many jobs its rough to figure them all out and write.

                        Naw, just kidding. I could write it on a piece of paper now. In pencile please. Thats all..

                        I like what You have Skill. I dont have that. I gather up here to learn from folks like you.

                        Thats all..JR.. .. JR

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                        • #42
                          Well I managed to get my butt out into the shop late last night to address some variables I wanted to throw into the mix.
                          Unfortunately no pics as my camera decided to toss me a memory card error message but no biggie, I'll deal with that another day.

                          No real dramatic changes but changes never the less.
                          I used a new shiny TCGT insert with a 1/32" nose radius and used every possible combination I would consider using as a finish pass. 235-750 SFM, .001"-.010" DOC, and feed rates between .0015"-.006", in addition to running it dry and with a lubri-coolant.

                          The best results I achieved, and they were significantly smoother if not more shiny than my previous pic, was by using a DOC of .002" 750 SFM and a feed rate of .003", wet.
                          Anything else I used with this insert/steel combination was significantly worse than those results I had originally achieved. Of course had I used the 4340 I have at hand the results would have been remarkably different. But it's not about that but the gummy material and getting an acceptable finish.

                          I realize that some of these results may be interpreted as being subjective but I'm here to please my expectations in the desired outcome and finished product so bare with me when I use descriptive and subjective terms like smooth or shiny. I think from past experiences most of us are on the same page here when it comes to using those terms.

                          Now the results obtained using the HSS vertical shear bit were much smoother and more shiny than before. This time the changes to the recipe included stoning the surfaces of the tool, sulphurized cutting oil, feed rate of .0015", .002" DOC and running right at 100 SFM.

                          I know there will always be some variables from my results to those achieved by others, but on this day in my shop this is what I achieved with my combination. I hope if nothing else this will inspire those not getting a satisfactory or desired result to try something else.

                          You know how the old saying goes about insanity. You know you're there when you keep doing the same things over and over while expecting different results.

                          The vertical shear bit I used is almost identical in profile to this one I grabbed at random from the net. I believe on mine the cutting edge is close to 40° off of vertical.The swarf it leaves behind is like fine kinky hair.

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                          Home, down in the valley behind the Red Angus
                          Bad Decisions Make Good Stories​

                          Location: British Columbia

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                          • #43
                            Still not fast enough for the carbide but you're getting there. With some of the really gummy low carbon stuff I've had to get up over 1,100 SFM to get a nice shiny smooth finish. Looking forward to the pictures.

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                            • #44
                              the TCGT results sound about right to me - I've never gotten shiny finishes with ground inserts on steel, but it is very smooth. Same inserts on alu gives a beautiful almost refractory finish. I tried grinding a shear bit once, but never got it to work right. To be honest, I found the application somewhat limited as you can't turn to a shoulder or face with a shear bit, both of which I do a bunch with CCGT inserts. I'm not so bothered by the lack of shiny finish, dimensional accuracy is usually more important.

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                              • #45
                                Have any of you fellows tried to make a shear bit from carbide? That might be interesting.

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