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  • Problems with toolbit sharpening

    Hi all. Im a total newbie to home machining and love tinkering. Ive watched a heap of tutorial video on toolbit sharpening for.my new flycutter and not sure what im doing wrong. Half way across the face of the steel that i am cutting the toolbit seems to round of the cutting tip and rides up onto.the qorkpiece. Im suspecting thats its a hard spot in the steel. Im facing just normal mild steel. Ive tried different speeds and feeds but it still happens. Any ideas... thanks.

  • #2
    Picture would help
    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

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    • #3
      Are you sure the bit is HSS?

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      • #4
        The surface feet per minute when using a flycutter can sneak up on you pretty fast and go way above what is kosher for HSS used even on mild steel. For example if your flycutter is set to a 3 inch diameter cut and we want to use 170 fpm as our cutting speed that's only 216 RPM. What RPM were you using?

        Now if it's some manner of mystery metal that does not mean that there won't be a hard inclusion of some sort. But I'd start with the basics and work from there.

        Now you also said you were making it about half way across the piece. How did the tool work up to that point? Did it just steadily get worse and worse much like a tool bit being eroded away by too extreme of conditions? Or did it do just fine up to the one point and suddenly pack it in?

        I had a piece like you're saying that had some hard spots. I faced it with carbide. But the hard spots in it were very noticeable as the cutter gave a "bump" even over the sound of the regular softer steel around it. So that can also be a hint of a hard spot.
        Last edited by BCRider; 09-08-2019, 07:22 PM.
        Chilliwack BC, Canada

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        • #5
          You may be getting the HSS too hot when grinding.
          If the tip of the tool starts to discolor, you have ruined the temper.
          Try to use a course wheel, like 80 grit and then a finer wheel to finish and then stone the surfaces.
          I like to rough my toolbits on a new 80 grit belt sander and that allows me to hold a ice cube against the toolbit to keep it cool
          If you use a water cup, have it right next to the wheel, not 2 or 3 feet away as some do, and when the water boils off the bit, stop and dip !

          Rich
          You did not say how big in diameter the flycutter is ?
          if 2 inches in diameter, then 250 RPM is about 125 Ft /Min...mild steel territory
          Last edited by Rich Carlstedt; 09-08-2019, 11:52 PM.
          Green Bay, WI

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          • #6
            Steel can have hard spots or inclusions. They can be harder than HSS and even harder than carbide tools. I hit one once with a drill bit and it was instantly destroyed. I tried another bit and it was also destroyed in seconds. I was able to rearrange that part so I filled that partial hole in and drilled in another place - after purchasing some more drills.

            Since you are doing a facing operation, I would suggest that you get another piece of stock and see how it works with that.
            Paul A.
            SE Texas

            Make it fit.
            You can't win and there IS a penalty for trying!

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            • #7
              Is it not a tramming issue ? Happens halfway.

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              • #8
                Originally posted by Rich Carlstedt View Post
                You may be getting the HSS too hot when grinding.
                If the tip of the tool starts to discolor, you have ruined the temper.
                Try to use a course wheel, like 80 grit and then a finer wheel to finish and then stone the surfaces.
                I like to rough my toolbits on a new 80 grit belt sander and that allows me to hold a ice cube against the toolbit to keep it cool
                If you use a water cup, have it right next to the wheel, not 2 or 3 feet away as some do, and when the water boils off the bit, stop and dip !

                Rich
                You did not say how big in diameter the flycutter is ?
                if 2 inches in diameter, then 250 RPM is about 125 Ft /Min...mild steel territory
                HSS doesn't mind bit of discoloration during grinding. Actually up to dull red hot gloving has little effect on temper.
                Tho grinding cracks can be a problem with aggressive grinding and water cooling just makes it worse.

                I'd start from looking from surface speed, HSS quality, steel quality and mill scale on steel.
                Location: Helsinki, Finland, Europe

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                • #9
                  Spindle speed was high at approx 1200rpm. It was actually.cutting very nicely up.to that point and no.matter.how i sharpen the cutter the same happe s hence my thoights about a hard spot. Thanks.

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                  • #10
                    Originally posted by Kiwipaulnz View Post
                    Spindle speed was high at approx 1200rpm. It was actually.cutting very nicely up.to that point and no.matter.how i sharpen the cutter the same happe s hence my thoights about a hard spot. Thanks.
                    If 1200rpm is not a typo you don't need to look any further! Flycutter of any diameter is going too fast at 1200rpm in steel.
                    Location: Helsinki, Finland, Europe

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                    • #11
                      Ahhh. I read somewhere that you cant run a flycutter fast enuf so gave it the boogey. Ill wind it back to 250 and see how it goes from.there. its just a wee 3inch flycutter and im really only.just shaving the surface. Tha ks.

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                      • #12
                        It looks like you found the problem, too fast! And if it is cutting good at the start it seems you are grinding the right shape tool. I will only add that after grinding you need to stone out the grinding marks with a smooth stone. Look at the edge with a 5 to 10 power loupe and you will see why.

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                        • #13
                          Originally posted by MattiJ View Post
                          HSS doesn't mind bit of discoloration during grinding. Actually up to dull red hot gloving has little effect on temper.
                          Tho grinding cracks can be a problem with aggressive grinding and water cooling just makes it worse.

                          I'd start from looking from surface speed, HSS quality, steel quality and mill scale on steel.
                          A trait of HSS is red hardness, I often made boring bars, by welding 5/16 HSS blanks to a bar to make boring bars. used an arc welder to weld. then grind my tip profile and use them.

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                          • #14
                            Originally posted by Kiwipaulnz View Post
                            Ahhh. I read somewhere that you cant run a flycutter fast enuf so gave it the boogey. Ill wind it back to 250 and see how it goes from.there. its just a wee 3inch flycutter and im really only.just shaving the surface. Tha ks.
                            Still a bit fast (~190SFM). Try around 120 to 150 RPM.
                            Location: Long Island, N.Y.

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                            • #15
                              As per Mattij and 754, once HSS is hardened there is no simple (non-industrial) way to soften it. To quote someone at Practical:

                              "HSS is, generally speaking, not anneal-able. If it were, breaking a drill or tap off would be no big deal... anneal it and drill it out. We all know that just doesn't work. You can actually MELT HSS with a torch, let it cool at room temp and it'll be, for all practical purposes, just a hard as it was before." The main problem with red heat, ie grinding a tool bit is the micro-cracking that can occur when water
                              quenched. On one of the alt.??machining?? (dunnoh which since the alt universe imploded in early '00s with flame wars) there was a post by a Carpenter Steel employee to the same effect.
                              Steve

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