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  • Newbie indexed carbide questions

    I thought I'd experiment with some indexed carbide. I hate grinding HSS bits (grinding wheels scare me - I'm always convinced they're going to explode!). Also I wanted to make some big steel bolts for attaching a small treehouse and it seemed like the right project to try on.
    I've got a holder (cheap Korean import) and some WNMG080408 inserts that fit it, and wasn't expecting much, but it's amazing compared to HSS. 1- 1 1/2" diameter EN3B mild steel. Running at 1500rpm or just under (aiming for c. 400fpm), and then experimenting with feed/depth of cut. 0.04"/revolution and 40-80/1000" depth of cut gave some really nice results with blue chips, no chatter, and (by my standards) a really nice surface finish.

    Where things went less well was when I tried to hit my finish OD. I had about 12/1000 to take off, and doing this at the same settings produced loads of sparks from the tool/workpiece, and both got really hot. Should I have changed speed/feed for this final cut, or can my cheap inserts just not cope with a shallow cut like this? If so how do you get around it? Is it a case of hitting final dimension from a distance or changing tool for the finish cut? Also do all these sparks mean I've ruined the corner on the insert?

    Pics below of the finish I was getting, some nice blue chips, and the insert after I made all the sparks with it.

  • #2
    Hi there! It sounds like your lathe is a lot larger and more powerful than mine. I am able to routinely shave 1/1000 at a time with my inserts, but only if its a fresh one. I use the CCGT 3252 mostly. The G in the designation denotes that it is ground to a sharp edge instead of molded. They were meant for working aluminum but the do great in steel as well.

    I think the only thing you could have done differently is to change to a fresh cutting edge. And perhaps slow the RPM down a bit for the finish cut. Sparks are never a good sign.
    25 miles north of Buffalo NY, USA

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    • #3
      Ok thanks. I wondered if the sparks were because of an edge that wasn't sharp enough just grinding away material on a thin cut, and it sounds as if that was probably the case. I hadn't realised the code difference between ground and moulded tips - thanks. I did try dropping the speed after I got all the sparks, but had probably already knackered the tip by then.

      The lathe is a second hand Harrison M250 I found, so nice and heavy and reasonably powered. Even so I was amazed how well it coped with such aggressive cuts.

      Comment


      • #4
        Originally posted by hollo View Post
        Ok thanks. I wondered if the sparks were because of an edge that wasn't sharp enough just grinding away material on a thin cut, and it sounds as if that was probably the case. I hadn't realised the code difference between ground and moulded tips - thanks. I did try dropping the speed after I got all the sparks, but had probably already knackered the tip by then.

        The lathe is a second hand Harrison M250 I found, so nice and heavy and reasonably powered. Even so I was amazed how well it coped with such aggressive cuts.
        Most likely, yes the tip was probably knackered by then. If you can, try the ground tips someday -- I think you'll like them. I switched over to them exclusively after trying them for just one hour, they are so much better especially for smaller lathes like mine. It takes far less power to make a cut because the edges are razor-sharp. The ground tips do require more attention in use -- they can break and get dull faster. I buy the very cheap Chinese ones on eBay at about $1 each.

        Nice lathe, the Harrison! Wish I could have found one locally just to have a geared head. Mine is a 1945 South Bend model A, very similar to the Boxford ME10.
        25 miles north of Buffalo NY, USA

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        • #5
          I would expect the sparking to be fixed by decreasing your feed rate. Especially for light cuts you'll get a better finish at low feeds. EN3B is like SAE 1020, so lets say we do a finishing cut with carbide, a light cut could be .005 and slow feed like .001 feed per spindle revolution. If your lathe can do 2005 rpm then that's the optimal setting.

          It's fine to run a tool at slightly less than the optimal cutting speed, but you run in to problems with tool life when you go above that reccomended speed. The most effective way to lengthen tool life is to decrease the feed.

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          • #6
            There are many different grades which vary in sharpness, you could try getting some intended for stainless steel and another lot intended for aluminium. As NSF mentions, the aluminium grade which are very sharp will work well for very light finishing cuts on steel. I buy the cheap Chinese inserts as they have improved greatly in quality in recent years. If looking for aluminium grade, one of the common codes is H01.

            I have just bought a box of SNGT 12 H01 inserts for £18 including postage, being square, they are limited in general application, but they do have 8 sharp edges per insert. I have ordered 2 extra holders for them, now that I have a choice of three different insert grades to use.
            Last edited by old mart; 07-12-2021, 10:20 AM.

            Comment


            • #7
              A very good point was raised about speeds and feeds.
              I think it helpful to remember that all those formulas and charts for speeds and feeds are written towards the industrial user, under ideal conditions. Therefore, when I switched to carbide, I experimented with a wide variety of types, speeds and feeds, ignoring what the books and formulas said.
              I found what works best for my specific lathe in my situation. It turns out to be 3x or 4x more than HSS,
              but that is still a far cry from what was recommended.
              Certainly my lathe isn't able to actually see the limits of what carbide can do.
              It simply wasn't designed for it.
              That said, it does use it effectively, just not as much as theoretically possible.
              25 miles north of Buffalo NY, USA

              Comment


              • #8
                A lot of inserts are not keenly sharp so they can remove heavy amounts without crumbling the edge. And that's why you got a nice cut and finish with the heavier cuts and less nice results while trying to remove .006" DOC for a 0.012" final reduction.

                There is a few ways to go with this. Generally the smaller the nose radius the smaller the minimum cut can be. I picked up a 10 pack of triangle inserts off Amazon to try with my old super cheap cutter set. The inserts that came with the holder set are pure junk. But I thought it might be nice to try a different insert. The new TCMT 16T304 have a pretty small nose radius which I found worked well for removing down to as light a cut as .002". But the finish suffers just like you posted in your trial.

                This seems to be a fairly common issue with inserts. The advice I got in a past thread of my own was to plan the cuts better so that the last pass to finished size was done with a cut of up around .015" DOC or so. That way the insert could work the way the designers intended.

                I found an online catalog for inserts that not only gave the size specs but also included the minimum DOC. The inserts with the sharper nose radii and better chip shapes were listed at minimums of down around .005 to .010. So that might help too. And sorry but I don't recall the name of the company and didn't save the link.

                Another option is to find some of the fairly extreme shaped inserts intended for finish cuts in aluminium. Something like THESE. You only want to use them for that last few thou though. For anything heavier the cupped edge is too weak and will break away when used on steel. But a lot of the others here have used this combination of regular for roughing then switched to these inserts intended for aluminium for the last fine passes for size with good results.

                I just put the ones shown in the link into my basket in fact to try out for myself.

                I can't imagine a metal shop without grinders. But I know how you feel. There's a little of that in the back of my mind too and I always stand to the side when switching the grinders on.

                But try as you might there's really no way to avoid HSS totally. I've made and used a pretty wide variety of form tools over the years which are simply not available as inserts under any circumstances other than perhaps special ordering. And at some point you'll run into this same need.

                I'm very much a carbide neophyte too. What I posted here is pretty well my sum total of success and a few things I've picked up from the others on here at HSM.
                Chilliwack BC, Canada

                Comment


                • #9
                  Ya know, I got a paper color copy of the Shars (DiscountMachine) catalogue.
                  It is nice to look at on the crapper. Seriously. Anyhow. got as cheap as the
                  various toolholders are at Shars, you are better to buy them new there.
                  And their toolholders have laser etched on them what carbide insert that they
                  take, and what screw they take, in case you bugger or loose one.
                  And keep that catalog so if you need a special holder or different nose radius
                  or backrake insert, it is all spelled out right there for you.
                  Normally I like major brand stuff, (Iscar, Kennametal, etc) but Shars is pretty
                  good for what you get, and the laser engraved insert numbers sold me on
                  their stuff.

                  --Doozer
                  DZER

                  Comment


                  • #10
                    on smaller lighter machines the molded inserts don't work so great as it's hard to get the DOC necessary to produce a good finish. I use them for knocking off nasty stuff, rust, weld beads that sort of stuff and the inserts are super cheap. I use the ground inserts for everything else, they work really well and the wear isn't terrible. I think I've gone through 3 boxes of CCGT inserts in 5 or 6 years.

                    On bigger lathes I've read that you need to calculate your final cut to be within the range that the insert is happy with. So if you need to take off 200 thou from the radius, take off 2 0.065" cuts, measure and adjust your final cut to end up at the final diameter. Those molded inserts really don't like taking skim cuts, they just bounce off the surface and smear material around.

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                    • #11
                      Originally posted by Doozer View Post
                      Ya know, I got a paper color copy of the Shars (DiscountMachine) catalogue.
                      It is nice to look at on the crapper.
                      ....
                      And their toolholders have laser etched on them what carbide insert that they
                      take, and what screw they take, in case you bugger or loose one.
                      ....

                      --Doozer
                      You too?
                      Every time I read the Shars catalog I check for corn.
                      I had a mind to buy a dozen ea of the screws.... look on the auction site, they are there.
                      WAY cheaper than the normal $4 ea. by the box full.
                      25 miles north of Buffalo NY, USA

                      Comment


                      • #12
                        These are the ones I use for Everything. Literally everything, including my MLA die filer.
                        https://www.ebay.com/itm/18472281969...YAAOSwbqlesJrw
                        They hold up OK to cuts as deep as .030
                        25 miles north of Buffalo NY, USA

                        Comment


                        • #13
                          I realise I've mixed up my depth-of-cut and diameter reduction figures in the initial post - I had a max 0.040" depth-of-cut to reduce diameter by 0.080", so apologies to anyone I have falsely given lathe-envy!

                          Thanks all though - lots of great information and suggestions. It makes perfect sense that an insert that can take off 0.080 at a time is going to have a tough/blunt edge that will only scrape on a 0.001 cut, and that I'll need a range of inserts to do everything. It also seems that insert tooling might be something of a rabbit hole to get lost down! I'll (try to) resist getting too drawn in for now though, and see what I can do to optimise feeds/speeds with what I've got. I'll have to keep up my HSS/grinding skills for the rest, and buy further inserts slowly as I go...

                          Comment


                          • #14
                            Originally posted by Doozer View Post
                            Ya know, I got a paper color copy of the Shars (DiscountMachine) catalogue.
                            It is nice to look at on the crapper. Seriously. Anyhow. got as cheap as the
                            various toolholders are at Shars, you are better to buy them new there.
                            And their toolholders have laser etched on them what carbide insert that they
                            take, and what screw they take, in case you bugger or loose one.
                            And keep that catalog so if you need a special holder or different nose radius
                            or backrake insert, it is all spelled out right there for you.
                            Normally I like major brand stuff, (Iscar, Kennametal, etc) but Shars is pretty
                            good for what you get, and the laser engraved insert numbers sold me on
                            their stuff.

                            --Doozer
                            I really like their catalog and etching too. The etching is really good for folks like my dad who struggles a bit with the desegnations. And honestly, at least for the larger stuff, a Kennametal holder doesn't really feel any nicer made.

                            Shars stuff is--at the worst--consistently decent.
                            21" Royersford Excelsior CamelBack Drillpress Restoration
                            1943 Sidney 16x54 Lathe Restoration

                            Comment


                            • #15
                              Originally posted by hollo View Post
                              I realise I've mixed up my depth-of-cut and diameter reduction figures in the initial post - I had a max 0.040" depth-of-cut to reduce diameter by 0.080", so apologies to anyone I have falsely given lathe-envy!

                              Thanks all though - lots of great information and suggestions. It makes perfect sense that an insert that can take off 0.080 at a time is going to have a tough/blunt edge that will only scrape on a 0.001 cut, and that I'll need a range of inserts to do everything. It also seems that insert tooling might be something of a rabbit hole to get lost down! I'll (try to) resist getting too drawn in for now though, and see what I can do to optimise feeds/speeds with what I've got. I'll have to keep up my HSS/grinding skills for the rest, and buy further inserts slowly as I go...
                              Are sure about. .040" for you feed? That's far too much. Only the heaviest of lathes, 40k lbs VMCs are taking that kind of feed rate, and are usually pulling off 1" or more in the diameter. I would keep hobby lathe level feeds below .02, and often below .01. I'll go with what makes a nice chip. I don't like CCGTs like Nickle. I do like CCMTs though. On a light lathe I will generally rough at .04-.08" off the diameter, and finish at .02. I feed at .007 and finish at .0035. For finish passes I avoid skim cuts, instead opting for a triple pass strategy. The first cut lets the spring out from roughing. The second cut lets the spring out from the heavier first cut. By the third cut the spring is more or less the same, and it cuts accurately.
                              21" Royersford Excelsior CamelBack Drillpress Restoration
                              1943 Sidney 16x54 Lathe Restoration

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