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Ok, now that I have the power..do I have the speed?? Carbide insert questions...

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  • Ok, now that I have the power..do I have the speed?? Carbide insert questions...

    If you happen to miss my lathe gloat..Please, let me do it again...

    Jet 1440-3pgh with a 7.5HP motor... Max speed is 1600rpm




    Now that I have the power...I am curious if I have the speed to run carbide inserts? I typically cut 4140HT that is 35hrc (I get it free)...

    From my researches it looks like that max speed of 1600rpm is to slow except for large diameter stock...

    I want to settle in my mind if I can use inserts effectively. Either I buy inserts, or a good grinder (I should have a good grinder anyways..)

  • #2
    The idea that you have to run high rpm to use carbide is a leftover notion from when all the carbide tools were negative rake and you were having to melt the metal at the cutting edge to bulldoze through the material. Modern inserts with positive geometry and chipbreakers now cut a lot more like HSS tooling. They will shear the metal so you don't need the high rpm. The new inserts are rated for higher rpm because they are very efficient and are often run on high horsepower spindles that can move a lot of metal very quickly for running production. Still, you can run positive inserts and solid carbide endmills at HSS speeds with perfectly good results. A heavy lathe like that can make good use of inserts. I find that a mix of HSS and carbide give the best results by using the tool most fitting for the job at hand.

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    • #3
      I'm using inserts to good effect on my Atlas Noodlelathe (tm). You'll be fine.

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      • #4
        Ok.. Recommendation on insert shape (type)? I am smart enough to read the charts from there I think. Also..I have a CXA tool holder on the way...look for 3/4 insert holders?

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        • #5
          Yup, look for a DCLNR124 or MCLNR4 for CNMG43x size inserts, the most commonly found ones. If you know you're going to do a lot of steels and want the best overall performance and value consider going to the 6-edge WNMG43x inserts and a DWLNR124 or MWLNR124 holder.

          That speed and HP is good for negative rake insert tooling, and you'll be pleasantly surprised at just how fast you can peel off metal now.

          BTW, the difference between MxLNR and DxLNR holders is the clamping system for the inserts. The newer DxLNR style uses a top clamp with an integral pin that reaches into the hole in the insert and a single screw pulls it back into the pocket. The older MxLNR style uses and eccentric center pin/screw and separate top clamp. Those often fill the eccentric screw's hex socket with chips, and you always have to have two wrenches handy. Those oder ones are more vcommon and available from cheaper sources, the new style ones are mostly available from quality tool manufacturers.
          Last edited by PixMan; 02-24-2013, 12:02 AM.

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          • #6
            Yes - 3/4 holders will work fine with CXA. There are lots of good brand names for cheap on eBay. Also, check Shars tools. They have good holders cheap too.
            I just bought a set of boring bars from them that I like. They are the SCLCR series with 80 degree diamond shape insert. Trigon inserts work good too. With the diamond and trigon you can turn and face without having to adjust the angle. This is mainly for finishing cuts as the insert is at a slight obtuse angle to the workpiece. If you try to rough like that the insert will want to dig in and go deeper. There are other holders that present the insert to the work at a different angle for roughing. With the right insert you can probably turn off 1/8 per side (1/4 on diam.) per pass on that lathe in mild steel.

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            • #7
              I've been in that building & YOU STILL SUCK!
              Originally posted by cuemaker View Post
              If you happen to miss my lathe gloat..Please, let me do it again...

              Jet 1440-3pgh with a 7.5HP motor... Max speed is 1600rpm




              Now that I have the power...I am curious if I have the speed to run carbide inserts? I typically cut 4140HT that is 35hrc (I get it free)...

              From my researches it looks like that max speed of 1600rpm is to slow except for large diameter stock...

              I want to settle in my mind if I can use inserts effectively. Either I buy inserts, or a good grinder (I should have a good grinder anyways..)
              "Let me recommend the best medicine in the
              world: a long journey, at a mild season, through a pleasant
              country, in easy stages."
              ~ James Madison

              Comment


              • #8
                A 7.5HP lathe with good tooling can easily peel off a .150" depth of cut at .012" per rev feed in even tougher 4140. My lathe is rated at 5HP, got perhaps 4 in reality and I can take .100" depth of cut in 316SS with a negative rake inert at 1200rpm and .0118" per rev. Steel is usually easier.

                I wouldn't buy a Shars holder because I'd want to know I could get parts for my holders tomorrow if I needed them. Good tooling doesn't cost, it pays.

                BTW, I'm surprised to see that machine without a foot brake for the spindle. Did it have one at the time it left the factory?

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                • #9
                  Originally posted by PixMan View Post
                  A 7.5HP lathe with good tooling can easily peel off a .150" depth of cut at .012" per rev feed in even tougher 4140. My lathe is rated at 5HP, got perhaps 4 in reality and I can take .100" depth of cut in 316SS with a negative rake inert at 1200rpm and .0118" per rev. Steel is usually easier.
                  Just for comparison, a chinese lathe with 8 kW motor on it and DNMG inserts (nose radius 0.8 mm) I can peel of 10-12 mm from the diameter (5-6 mm DOC) with 0.3 mm feed per revolution and coolant running, same prehardened stuff.

                  You don't need the speed so much with a carbide, though the excell at higher speeds. Good indication is to take cold rolled and peel it off with 'too low' speed and the surface looks like a little torn albeit still smooth feel. Crank up the RPM up to what you got and take another peel and the surface shines
                  Amount of experience is in direct proportion to the value of broken equipment.

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                  • #10
                    Originally posted by PixMan View Post

                    BTW, I'm surprised to see that machine without a foot brake for the spindle. Did it have one at the time it left the factory?
                    It did..in my original thread I said that I want to fix that

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                    • #11
                      I used to use Carbide insert tooling almost exclusively on my old Myford ML7, and that had a top speed of 640rpm, no problems at all and beautiful cuts & finishes.
                      My Colchester Bantam only has a top speed of 1600 and I use Carbide exclusively on that too, apart from one HSS parting blade, and tbh I donlt often run it over 1000rpm.
                      You'll be fine.

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                      • #12
                        Speed? It's not "speed", it's SFM. Your machine is rigid enough, but you won't turn much below 3/4 inch diameter if you want surface quality and chip breaking.

                        SFM depends on the diameter turned. I aim for 350-800sfm (insert and material dependant) . Most of my toolling is negative rake, BUT most of the finishing grades are positive rake (and/or approaching positive) in the negative holders. Some I can take a miniumum cut of 3-4 thou (finishing grades), some it's 15-20 thou. I can throw chips way way deeper than that at decent feed rates (14x40, 4kw motor)!. I mainly use WNMG, with DNMG close behind.

                        1 inch at 1250 rpm is 327sfm. I figure that's the minimum sfm for most of my carbide. On the other hand... 6 inches at 250 rpm is 392sfm.
                        Last edited by lakeside53; 02-24-2013, 03:07 PM.

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                        • #13
                          Originally posted by lakeside53 View Post
                          Speed? It's not "speed", it's SFM.
                          Yes, surface speed to be exact.
                          Amount of experience is in direct proportion to the value of broken equipment.

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                          • #14
                            And you get free steel????

                            You really, really suck.

                            How did you get that little sweetheart arrangment?

                            troy

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                            • #15
                              that is a large chunk of lathe
                              https://www.flickr.com/photos/csprecision

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