Announcement

Collapse
No announcement yet.

Carbide question

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Carbide question

    I have always been told that carbide likes a good heavy cut at a fast feed and speed (This is a relative to the material being cut) and do not do well with interrupted cuts. With a lathe tool you can dig in and go but on an carbide end mill or face mill with anywhere from 1 to 8 or more inserts don't you have an interrupted cut on each insert per rev. What keeps the inserts from breaking down to fast or do they have a lower live expectancy then lathe carbide inserts.
    The shortest distance between two points is a circle of infinite diameter.

    Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

    Southwestern Ontario. Canada

  • #2
    Different grades of carbide are for different applications!

    Milling grades of carbide are tough, tolerate interrupted cutting and thermal shock very well.

    Turning grades are better suited to long, hot continuous cutting.

    The amount of cobalt (the binder or glue in tungsten carbide inserts) reduces the wear resistance, but increases the toughness or strength.

    That is, an insert with 10%-15% binder is tough, because there is more "glue" holding the particles of tungsten carbide together; but would wear quickly in a continuous cutting application.

    An insert with 3% cobalt wears quite (in a continuous cut) well because there is less "glue" and more hard tungsten carbide in the matrix. However, it is fragile (in an interrupted cut) because the particles are not well bonded by the minimal amount of "glue."

    There are other factors, too, but all carbide is not equal!

    Mike

    Comment


    • #3
      All of my milling cutters are positive inserts. Even both my 6" shell mills. The inserts do not last long. My lathe inserts are negative and are tough as hell.
      I do a lot of weld build up and turn it on the lathe. The carbide inserts last really well even with all the interupted cuts.
      Heavy cuts... well I suppose. With razor sharp HSS I can wisk off .001 easy. With inserts I'm lucky to get .003 or so depending on the condition of the insert etc. A brand new edge will get me .002 for a bit. ,003 or ,004 is a safer bet as you never really know when you'll get .002.. at least on my sorta shaky 14X40.
      Russ
      I have tools I don't even know I own...

      Comment


      • #4
        These days you can get really sharp carbide inserts like CCGT's that will make those superfine cuts. They'll take off "dust" if you want to.

        These inserts look like this and are extreme positive rake:



        That particular one is off a boring bar. The CCGT's will fit CCMT tooling.

        Originally such inserts were for aluminum, but nowadays there are grades available for steel. They're not too happy with a really ugly interrupted cut--not sure I'd use them on a tough weld or some such--but they generally work really well. I keep this plus some regular CCMT's for the tougher roughing work.

        A lot of folks will also keep an inexpensive diamond hone and use it to resharpen the edge of a slightly dull insert or brazed carbide tool.

        Cheers,

        BW
        ---------------------------------------------------

        http://www.cnccookbook.com/index.htm
        Try G-Wizard Machinist's Calculator for free:
        http://www.cnccookbook.com/CCGWizard.html

        Comment


        • #5
          Originally posted by BobWarfield
          A lot of folks will also keep an inexpensive diamond hone and use it to resharpen the edge of a slightly dull insert or brazed carbide tool.
          A diamond hone is also nice to take off the TiAN/TIN/TiACN coating from the insert. The coating is for high speeds and feeds, but it rounds off the sharp edge on the insert.

          I try to buy uncoated inserts, which tend to be much sharper, but they seem to be pretty rare.
          "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

          Comment


          • #6
            I also really like the CCGT inserts that Bob posted above. I can grind a HSS bit fairly well. But those ccgt's work to good for me to mess with hss anymore unless I need a form tool. They work great even on my 100 year old Artisan, and VERY good on my SB9.They'll work just fine with the slower spindle speeds on the older machines. Best used for finishing and stick with the ccmt for roughing.
            Steve

            Comment


            • #7
              The 2" dia face mill I'm looking at uses TPG32* inserts, the same as used on lathes (the specs don't give the amount of binder in them) but it sounds as if they won't last long enough to make it worth the while, I might be better off sticking to HSS. end mills.
              The shortest distance between two points is a circle of infinite diameter.

              Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

              Southwestern Ontario. Canada

              Comment


              • #8
                Is there a grade associated with or after the insert number: C2, C6, KC810, 883, GC4015, etc?

                Mike

                Comment


                • #9
                  Originally posted by loose nut
                  The 2" dia face mill I'm looking at uses TPG32* inserts, the same as used on lathes
                  Most of those cheap TPG face mills have no axial or radial rake angle: the carbide insert sits flat in the pocket, and perpendicular to the shaft. Because there's no approach rake, they absolutely hammer the mill (which is really hard on the spindle bearings), and leaves a ratty finish.

                  I bought one of these when I didn't know any better, and it's now relegated to rough milling. See how the insert is flat against the pocket? The insert hits the workpiece flat and batters the machine. The TPG face mill in this picture is spinning at about 200 RPM:



                  The Dolfa and Grizzly TPG face mills are more expensive, but the pocket is angled with respect to the shaft, so like a helical mill, there's a gradual contact of the insert with the workpiece. So they don't hammer the machine, and are much smoother, and leave a much nicer finish.

                  This is one of my Sandvik RA-290 "shear mills" with high axial and radial rake angle. Look how the insert is tilted back in the pocket, and the pocket itself is angled backward with respect to the shaft. This type of face mill is made specifically for low horsepower, low rigidity machines, and leaves a mirror smooth finish:

                  "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                  Comment


                  • #10
                    Lazlo, I picked up a cheap one, 2" Dia. 3 inserts, for $29.00, just to try without spending a fortune if it didn't work out. On a piece of plate, 570 grade I think, at low speed you really get that thump, thump, thump that you mentioned, so I ramped the speed up to about 600 rpm's 0.025" DOC, just to see what would happen and the cutting smoothed out, the finish was a bit rough but my travel could have been a bit fast. After that I cranked the speed up to about 1300 rpm's and took a .005" finish cut with a slower feed and the finish was quite good for the type of material. The cuttings were not even turning blue at this tool loading. I know the rpm's were way to high but it seemed to work very well. If this works out I may get one of the face mills you mentioned but for hobby work I really don't need (want yes, need no) that kind of capacity.
                    The shortest distance between two points is a circle of infinite diameter.

                    Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

                    Southwestern Ontario. Canada

                    Comment


                    • #11
                      Hi,

                      No, your rpms weren't too fast. At 1300 rpms, you would have been in the neighborhood for a 2" cutter. I regularly run a 4" with 8 TPG-432 inserts at 850rpms and depth of cuts to .700" in S7, D2, and 4140 steels. And no coolant. Insert life is good.

                      I suspect the reason why most people have a hard time getting good results with these cutters is they don't run them fast enough and hard enough.

                      So when you use that cutter, or most carbide insert shells, kick that pig! Don't be afraid to push it. That's what they need. And why they exist in the first place.

                      dalee
                      If you think you understand what is going on, you haven't been paying attention.

                      Comment


                      • #12
                        Originally posted by dalee100
                        So when you use that cutter, or most carbide insert shells, kick that pig! Don't be afraid to push it. That's what they need. And why they exist in the first place.

                        dalee
                        So what speeds and feeds should I run my 3" face mill with 4 cutters??

                        Aluminum.............??

                        Steel..................??
                        Ernie (VE7ERN)

                        May the wind be always at your back

                        Comment


                        • #13
                          Hi,

                          A lot is going to depend on how rigid the setup, and how much HP is available at the spindle. So common sense and experience is needed.

                          But lets' use a standard BP type mill with 1 1/2 to 2 HP at the spindle, and a Kurt vice machining steel. As you found, your 2" cutter ran pretty good at 1300rpms. Depending on the material and depth of cut and feed rate, I would run between 1000 and 1500rpms. A roughing depth of maybe .100" with most BP's and a solid vice or clamped setup could run at 3" to 4" a minute in a face milling cut. You want faster feeds, reduce depth of cut until you achieve your desired feed rate.

                          A 3" cutter in steel, I run 800 to 1100rpms. You would want to probably lighten up your depth of cut to maybe .050" to .075" to maintain a 3" to 4" feed rate.

                          Thoughts to keep in mind. Tool steels generally "chip" better than mild steels, (mild steels can sometimes be "sticky" causing the chip to "smear" across the work surface leaving a poor finish), giving a better finish and tool life. Try to leave .030" to .050" for a finish cut. .005" finish cuts are hard on inserts. It causes heat build up and that accelerates wear on the edges. Always run as much feed rate as your set up will allow. You want a nice deep blue colored chip. Stay away from coated inserts in these cutters. They tend to "slap" harder than the shells with the higher rakes like the Sandvik that lazlo showed. Cheap plain ground inserts are best.

                          I wouldn't use this style of shell mill for aluminum unless it was all I had. They are really meant for steels and not "light" metals. Aluminum generally requires high shear angles to prevent edge build up and material welding. IF I was going to try it though, this might be the place to use a coated insert, (maybe TiN), I would maybe max out the rpms, use a light depth of cut, perhaps .025" to .050", and all the feed I could muster. But, I would expect problems.

                          ------ Sorry, my train of thought is gone, on what I wanted to say. Was interrupted by an ambulance call.

                          Mostly the HSM suffers from two things with these cutters. Light weight, low HP machines, and an unwillingness to push the inserts hard enough.

                          dalee
                          If you think you understand what is going on, you haven't been paying attention.

                          Comment


                          • #14
                            Originally posted by dalee100
                            No, your rpms weren't too fast. At 1300 rpms, you would have been in the neighborhood for a 2" cutter.
                            A 2" cutter at 1300 RPM is around 700 surface feet per minute -- that's WAY too fast for a home-shop machine!

                            Mild steel is recommended at 130 - 180 surface feet per minute with a HSS insert, which is 250 - 350 RPM with a 2" facemill. You definitely want to be in that lower range for a low horsepower, low rigidity machine.
                            Last edited by lazlo; 05-04-2008, 08:19 PM.
                            "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                            Comment


                            • #15
                              Now guys you have me all confused, is it to fast or to slow.





                              The first picture shows the new milling cutter, and unlike the one in Lazlos picture it has some rake although not as much as his more expensive face mill.
                              The second picture is a piece of boiler plate which I had handy and used as a quick test, It looks better in real life and it has a smooth to touch finish, a better piece or material would get better results.
                              The tooth drag as it follows around leaves slight uneven marks.

                              I know that carbide is suppose to be run hard but sometime I can get a better finish by taking a light cut at high RPM'S.
                              The shortest distance between two points is a circle of infinite diameter.

                              Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

                              Southwestern Ontario. Canada

                              Comment

                              Working...
                              X