Announcement

Collapse
No announcement yet.

How much difference can tooling make on a small, low power lathe?

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

  • #16
    Originally posted by Evan
    The rake refers to the top surface of the tool only and the angle it has relative to the work (when correctly applied).
    With inserts, "positive" or "negative" refers to the way the combination of the insert and the toolholder position the cutting angle in relation to the workpiece.

    Which is why a "negative" rake insert like the SNGA you're using has vertical sides: the combination of the square sided insert with the corresponding toolholder (like you've made) that tips the insert down creates the negative rake angle.

    So you can take a negative rake insert with a positive rake chipbreaker, and the combination of the insert angles and the toolholder pocket make a positive rake tool, like Ted Edwards' famous lathe toolholders:

    http://www.metalwebnews.com/howto/to...oolholder.html
    Last edited by lazlo; 07-06-2009, 12:20 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


    • #17
      Great post Evan :up:

      How does one overcome the problem of making interrupted cuts with carbide insert tooling so that the insert doesn't chip - or is it a case of 'no can do'?
      Peter - novice home machinist, modern motorcycle enthusiast.

      Denford Viceroy 280 Synchro (11 x 24)
      Herbert 0V adapted to R8 by 'Sir John'.
      Monarch 10EE 1942

      Comment


      • #18
        With inserts, "positive" or "negative" refers to the way the combination of the insert and the toolholder position the cutting angle in relation to the workpiece.
        That is what "correctly applied" means.

        You could use that exact same insert, and cut the toolholder pocket to tilt it up, and make it a positive insert.
        No you can't. It has zero clearance. It must be presented at a negative angle to cut.
        Free software for calculating bolt circles and similar: Click Here

        Comment


        • #19
          Originally posted by Evan
          No you can't. It has zero clearance. It must be presented at a negative angle to cut.
          Red Ted Edward's article -- the chipbreaker gives you the clearance. All that matters is the final angle that's presented to the workpiece.
          "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

          Comment


          • #20
            Originally posted by lazlo
            Red Ted Edward's article -- the chipbreaker gives you the clearance. All that matters is the final angle that's presented to the workpiece.

            The inserts in the article by Ted Edwards are of the positive/negative rake type, which is different than the negative rake insert that Evan is using. Evan is correct. There is a good drawing of this in Machine Shop Practice vol 1.

            ME

            Comment


            • #21
              How does one overcome the problem of making interrupted cuts with carbide insert tooling so that the insert doesn't chip - or is it a case of 'no can do'?
              That really depends on the grade of carbide. Not all carbide grades chip easily. I often use solid C1 carbide cutters that are recommended for heavy intermittent roughing cuts in sand cast iron. The pieces I have are very old stock originally used for debarker machines and must withstand hitting rocks. They not only don't chip easily but when they do they expose a fairly good cutting edge as they tend to flake off the underside of the top face when they chip.

              This insert had no problem with cutting the weld line when I bored the inside. It still shows no wear.
              Free software for calculating bolt circles and similar: Click Here

              Comment


              • #22
                Originally posted by Michael Edwards
                The inserts in the article by Ted Edwards are of the positive/negative rake type, which is different than the negative rake insert that Evan is using.
                They're both negative rake inserts with flat sides. The only difference is that the TNMP insert that Ted uses has a postive rake chipbreaker, which gives you the clearance to tip the negative insert enough to get a positive rake angle. So Evan's SNGA negative insert has the profile (flat sides) of the top insert (sans the chipbreaker groove), and Ted Edward's negative insert has the middle profile, and he tilts the insert down 5° to get a positive rake.

                You could use a more severe chipbreaker like the TNMS insert at the bottom, tip the insert even more (10°) and get even more positive:

                Note that these are all negative rake inserts:

                Last edited by lazlo; 07-06-2009, 12:53 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


                • #23
                  Thanks for the super info Evan, great post. I have good luck with TNMG and the ones I use don’t seem to mind interrupted cuts.

                  Cheers, Bob

                  Comment


                  • #24
                    Before everyone runs out and purchases tool holders and anything that says "Cermet", Cermets are classified in the Carbide family, but are their own thing. Not all Cermet inserts are the same, just as not all Carbide inserts are the same. There are many compositions, chip breaker configurations, and edge preps. I have been using them for years and have a variety of different types, all of the same insert style. Some are sharp edge, some are honed edge, all sorts of different chip breakers and land widths, etc, and all perform differently on different substrates. To make a statement that all Cermets work and everyone should try some is like saying all dogs are brown. Evan's calling his a Cermet coated carbide is also a bit misleading as Cermet is not a coating. Evan's inserts are most likely bare Cermets (not meant to criticize Evans statement). Cermets do however come with coatings on them and are able to run at much higher surface speeds than carbide as they are much more heat resistand and durable. Cermet is also nothing new, as it was first developed in the 1920's, however, it has been developed and refined considerably since, as has Carbide.

                    Just a warning, so do a little research before you grab the first pack of Cermets you see on eBay and have less than acceptable results!

                    However, as Evan discovered, with the right combination of insert, substrate, and surface speed, they are near impossible to beat for a nice finish!
                    Last edited by Glenn Wegman; 07-06-2009, 02:18 PM.

                    Comment


                    • #25
                      that is a great finish quality for pipe.

                      Comment


                      • #26
                        Originally posted by Evan
                        Gary,

                        That is my electric power crossfeed drive. I have variable speed reversible power drives on both axes.
                        Cool! Thanks!

                        Gary

                        Comment


                        • #27
                          Originally posted by quasi
                          that is a great finish quality for pipe.
                          Yes, definitely! I'm really curious about trying Cermets now too

                          Glenn: I've read in the trade rags that modern Cermets are a whole lot more durable than they were just a couple of years ago -- has that been your experience?
                          "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                          Comment


                          • #28
                            Lazlo,

                            I needed to turn a part that was 2" diameter, 46RC, and had two keyways cut in it. I used a coated cermet at 1200 rpm and it did just fine. It's by far the most durable Insert I have used. It was a Sumitomo T2000Z and was not the recommended grade for an interrupted cut, which would have been a T3000Z so I can't imagine how tough that one must be!


                            Here's another example.

                            I've always been a Carbide guy and am constantly hearing how HSS is superior for finishing due to it's sharpness, bla bla bla. I cut this piece of steel stock from right to left to the shoulder with a fresh stoned HSS tool bit because I got tired of hearing about it. I then went over it half the distance with my favorite negative rake Cermet insert at .001" doc with coolant and got a near perfect finish as you can see. The .001" doc is because I got tired of hearing how you can't take light or finish cuts with negative rake inserts. It's just a case of having the right combination! The biggest problem that I see is people that have used HSS forever decide to try Carbide so they go get a Chinese brazed tool bit from Harbor Freight or some generic inserts off of eBay and try to use them like they do HSS and get terrible results, and then can't wait to tell everyone the carbide doesn't work! HSS is HSS and the grinding/sharpening is the difference between success and failure where with Inserts there are literaly thousands of different grade, configuration, speed, feed, combinations that all play a part in getting the right finish.


                            Glenn
                            Last edited by Glenn Wegman; 07-06-2009, 05:00 PM.

                            Comment


                            • #29
                              Originally posted by Glenn Wegman

                              HSS is HSS and the grinding/sharpening is the difference between success and failure where with Inserts there are literaly thousands of different grade, configuration, speed, feed, combinations that all play a part in getting the right finish.

                              Glenn
                              No doubt the carbide vs HSS debate will rage on and on.

                              I've had very mixed results and I've gotten stuck with some inserts sold only in 10's from the supplier in the big city 2 hours away from my shop that are worse than dull HSS. They squeal, don't cut freely, and leave a finish that looks like it was gnawed on by rodents. Having said that, the same supplier sold me some others that work well, cut freely, leave a good finish. My point is this, I have neither the time nor resources to go through all the 100s of combinations of carbide to come up with something that works. For the price of an insert, I can buy a HSS blank and change it as I need to to get acceptable results...
                              Design to 0.0001", measure to 1/32", cut with an axe, grind to fit

                              Comment


                              • #30
                                Glen,

                                I misinterpreted the listing of those inserts when I looked them up originally. This is what I read when I checked them out. Note the category on the left.



                                It is however a TC30 grade cermet intended for high speed machining and fine finishes.
                                Free software for calculating bolt circles and similar: Click Here

                                Comment

                                Working...
                                X