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Sharpening Carbide Inserts?

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  • Sharpening Carbide Inserts?

    Is this even possible? When I first bought my lathe, I bought a set of carbide insert bits from Harbor Freight or similar. They seem to be as dull as a spoon - I can't even get them to cut aluminum. What type of wheel would do this?

  • #2
    You didn't fall into the trap of buying those really cheap ones made in Scotland from old last years shortbread biscuits. Seriously China sell some that are very brittle Being hard does not mean they will not dull up when slicing Thrud's sisters meatloaf ,God rest his beautiful kind soul, He was the best I really miss talking to him by phone. Alistair
    Please excuse my typing as I have a form of parkinsons disease

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    • #3
      Originally posted by Fritz1255 View Post
      Is this even possible? When I first bought my lathe, I bought a set of carbide insert bits from Harbor Freight or similar. They seem to be as dull as a spoon - I can't even get them to cut aluminum. What type of wheel would do this?
      You can sharpen them with a diamond disk in a dremel tool. If they are uncoated I used to use a diamond finger nail file to hone the edge. I've since bought diamond hones made for sharpening knives and find they do a good job.

      Many generic carbide inserts are molded and not really sharp. That works fine with a powerful lathe since you can literally plow through metal because of the way that it fractures. The duller edge lasts longer. With less power you need sharper edges to do more shearing and less plowing. Make sure that you leave that 7 to 11 degree slant (known as relief) on the front and sides

      You want to make sure that your carbide is right at the center of the lathe's axis. An easy way to be sure is to put a dead center in the tailstock and then use the point of that as the reference for the top of the cutting edge.


      Dan
      At the end of the project, there is a profound difference between spare parts and extra parts.

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      • #4
        Every so often I learn more about carbide inserts. One fact I learned is that many of them are deliberately made with a slight rounding to the edge so they are more durable. But they do this knowing that they will have to be used with a minimum depth of cut. That may be the ones you bought. They rely on sizing down to a measurement than taking the last cut to size of some minimum amount like .010 or more and leave you at the proper size. If you're used to HSS where you can take off half a thou then you will find that you can't. You end up burnishing the surface at best and simply gall the hell out of it at worst.

        The worst for this trait seem to be the negative rake cutters where they do not have a top relief groove to simulate a positive rake sort of cutter. Often the negative rake cutters will have such a groove but it's back a few thou from the actual edge and with the right light and magnification or darn good eyes you can see a little "shelf" of this negative rake top surface. Those are the ones that need some minimum depth of cut to work decently. And I find that even with that they spring the work away and if you don't retract the cross slide and wind the carriage back they will often cut a spiral groove due to that pressure against the work.

        So the mystery is in finding the right inserts with either a positive rake and sharp edge or that have negative front rake and the right "sharp" positive rake groove in the upper and lower faces. As a guide if you look through a big insert data book some will indicate the minimum depth of cut. And often as not those have the most generous tip radius.

        Of course none of this helps you with your present inserts. But the others already mentioned diamond slips or wheels.

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        • #5
          If the diamond wheel was bought from Harbor Freight too...

          OK, I digress.

          Throw the garbage away and buy good ones. Don't waste your time trying to make a candy out of horse sh1^. You can find inexpensive brand name inserts on eBay.

          P.S. I assume that your judgement is true, and you're not using those inserts on a HF lathe.

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          • #6
            Possible to sharpen? Yes.
            Sensible? so-so.

            If you sharpen from the top you lose the chip breaker. If you sharpen from the (all) sides the insert fit to the pocket is loose(assuming screw mounted inserts)

            And as stated earlier the carbide inserts are "dulled" on purpose.

            If you want cheap and sharp carbide inserts go to ebay and order aluminium specific inserts from china/ebay. CCGT, DCGT, TCGT are the types to look for.
            (PS. super cheap inserts from china/HK are counterfeits but work suprisingly well. Korloy seems like the most common counterfeited brand)

            Edit: Banggood is also mentioned countless times on this forum, here is their offerings on sharp inserts:
            https://www.banggood.com/search/h01-insert.html
            Last edited by MattiJ; 12-30-2017, 05:25 PM.

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            • #7
              Originally posted by Fritz1255 View Post
              Is this even possible? When I first bought my lathe, I bought a set of carbide insert bits from Harbor Freight or similar. They seem to be as dull as a spoon - I can't even get them to cut aluminum. What type of wheel would do this?
              Not a wheel but instead a diamond coated sharpener, one you might use to sharpen your pocket knife. Start with coarse or medium, then finish with fine. This set of 3 is what I use.

              https://www.harborfreight.com/3-piec...cks-36799.html

              The question you didn't ask is if it is worthwhile to do so. You'll be trading your time for saving money. If you have the time it may not take much money. Once sharpened the carbide will cut a lot before it dulls and if you have sharpened it once, you can do it again.

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              • #8
                One assumes that they're brazed on carbide rather than replacable inserts. They can be reshaped with a resin bonded diamond wheel or a diamond hand lap, they can be touched up with a lap made from a disk of cast iron held in the lathe chuck with diamond paste pressed into it using a ball bearing as a roller.

                If they are replacable inserts then, if they've got a chipbreaker, it's hard to resharpen them without spoinling the insert. If they don't have a chipbreaker, they should normally only be used for cast iron and similar materials.

                Basically, get some new inserts or get some holders that take inserts. CCMT21.51/CCMT060204 inserts are a couple of dollars a piece, barely worth the bother of sharpening.
                Location- Rugby, Warwickshire. UK

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                • #9
                  What I have looks like this: https://www.harborfreight.com/5-piec...set-90741.html

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                  • #10
                    I've touched up inserts before to chew through some tough stuff, or ground a more positive angle for cutting aluminum from steel inserts before. It's possible, but not really done because in doing so, you're ignoring the whole purpose of a replaceable insert in the first place. If you're doing this on a regular basis you probably better off buying brazed carbide, or HSS toolbits. If you've got holders, then just buy the proper inserts for the material you will be cutting.

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                    • #11
                      Originally posted by Fritz1255 View Post
                      Those are the "brazed tools" mentioned by some above. "Inserts" implies that they use the separate carbide inserts held to a holder with a screw or clamp in the case of inserts with no center hole.

                      The issue with these cheap sets is that some are OK and others simply won't take an edge of any sort. But you need to give them a fighting chance by using a diamond wheel or at least a green silicon carbide wheel and then hone then with a diamond lap. If you try to sharpen them on the regular stock wheels I found early on that the edge ends up all broken down and eroded back in some manner and they are sharp as a spoon as a result....

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                      • #12
                        You’re wasting time and money.

                        Good quality inserts will last a long time.
                        Gary


                        Appearance is Everything...

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                        • #13
                          Originally posted by goose View Post
                          You’re wasting time and money.

                          Good quality inserts will last a long time.
                          That's quite true, depending on how they are used. In production settings they dull before the day's shift is over.

                          In home shop use mine last for many months. Then I do something stupid and chip one. But I have had some name brand that dulled after a few weeks of use heavy use. Use is generally rated in hours of turning time.

                          Dan
                          At the end of the project, there is a profound difference between spare parts and extra parts.

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                          • #14
                            For best results you need a dead sharp edge. Stay away from anything that has a honed edge.
                            I made a small fixture for holding carbide inserts. I sharpen them on my surface grinder.
                            I did start a thread with pictures but thanks to dump bucket the pics are probably gone.

                            JL...................

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                            • #15
                              There are times where sharpening an insert can be helpful.

                              I read a post over on PM by HuFlungDung ...practicalmachinist.com/.../getting-good-finish-carbide-inserts

                              His shop sharpens worn inserts to a sharp edge for fine finishing. They allow you to cut .0002 to .005.

                              I used a air pencil grinder and a set of 600 grit diamond burs to give it a try. It works and the inserts cut just fine.

                              I recently picked up a Baldor carbide grinder and have a diamond wheel on it. I have a couple more ideas to try.

                              TNMG inserts are cheap, but so am I, so getting three more cutting edges for a couple minutes work makes sense to me.

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