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Thread: Problems with toolbit sharpening

  1. #1
    Join Date
    Sep 2019
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    Default 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. #2
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    Picture would help
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  3. #3
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    Are you sure the bit is HSS?

  4. #4
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    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 at 07:22 PM.

  5. #5
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    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 at 11:52 PM.

  6. #6
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    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.

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

  8. #8
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    Quote 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.

  9. #9
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    Sep 2019
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    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.

  10. #10
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    Quote 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.

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