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Sharpening Your End Mills

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  • Sharpening Your End Mills

    Got around to sharpening some of my end mills that have been slowly collecting by the grinder. I don't have anything fancy to sharpen them with, just the fixture you see in the picture, and my surface grinder. There are a couple different types. Some are center cutting and some are not. The center cutting ones, #4 in the picture, after a couple sharpenings you have to start to cut a clearance slot as I usually do with a dremel tool. It doesn't have to be perfect, just has to open up the center. The other cutters #2, & 3 with the hole in the center have to be x'ed out after several sharpenings. As you can see that #2 only has a small hole left as that one has been sharpened several times, so I had to x that one out a bit. But what has me stumped is #3. Look at how the edge tapers out to the end, while all the others are relativley straight. I've tried grinding it at different positions relative to the wheel but always end up with the same result. I've come to the conclusion that it's in the geometry of the helix altough you cant really see any difference looking at it compared to the others. On the good side of things they always cut super nice when I'm done regardless of how they look. The last one,(not done) broke at one time. It had a hole in the center which is now gone. I'll have to either x it or grind a hole in the center when I go to sharpen it. Thought....... anyone??

    Note: The alternative to x ing out the center is a relief cut angled into the center as seen on #1 and #4, but that would require another set up to do and the x serves the same purpose and is faster to do.

    I haven't reied doing any of these on the tool and cutter grinder yet, and I don't have an air bearing for the flutes. Yet !






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

  • #2
    Awesome job Joe and great pictures!

    I have one of those little fixtures but no surface grinder yet. I rigged up an X/Y table with the fixture bolted to it to "offer" up endmills to the wheel on my H/F carbide grinder and I actually sharpened a couple. The "gashing" process gave me fits and I gave up. Never thought to try it with a Dremel like you did!
    Milton

    "Accuracy is the sum total of your compensating mistakes."

    "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

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    • #3
      I sharpen my end mills the exact same way. Only I do not have a fixture like yours, wish I did. I drilled end mill diameter holes in a block of steel at 5 degree angles in one direction and 1 degree the other direction. I put the end mills in the holes and tighten a set screw on the side to hold it in place. I put the 4" square metal block on the surface grinder and dust off the first end mill. Once I get things setup all I have to do is loosen the set screw and rotate the end mill 90 degrees to grind each cutting edge. Then I swap out the sharpened end mill for another one that needs to be shapened. I do all the same type end mills first like all 1/2 first then 5/8 then 3/4 then 3/8 etc. It works good and its pretty fast too. I save my end mills so I can sharpen about 5 or more of each size.

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      • #4
        I find it weird the flute tips are not straight, doesnt that alter the cutting height of the endmill a little? Seems to me it would cut deeper in the center then the outside as the cutting edge recesses back a little. (unless im reading the geometry wrong)
        Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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        • #5
          Originally posted by Black_Moons
          I find it weird the flute tips are not straight, doesnt that alter the cutting height of the endmill a little? Seems to me it would cut deeper in the center then the outside as the cutting edge recesses back a little. (unless im reading the geometry wrong)
          Interesting point!
          John M...your (un)usual basement dweller

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          • #6
            Yes, but what's the feed rate ? Looking at cutters no 1 and 2 in the photo, the curved end cuts first, and then the centre straight portion cuts deeper. You'll never use a feed rate/rpm combination that lets any of the work get missed by the centre portion.

            It seems like the intention is to do a shallow cut followed by a deeper cut, although the difference is marginal, anyway.
            Richard - SW London, UK, EU.

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            • #7
              There should be end relief towards the center axis so the corners are the deepest into the cut.

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              • #8
                I would sure like to know more about the jig used for sharpening endmills on a surface grinder. I have a surface grinder and a collection of dull/damaged endmills... seems like the only thing I am missing is the jig.
                Video meliora proboque deteriora sequor

                www.garagegunsmithing.com

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                • #9
                  Originally posted by rohart
                  Yes, but what's the feed rate ? Looking at cutters no 1 and 2 in the photo, the curved end cuts first, and then the centre straight portion cuts deeper. You'll never use a feed rate/rpm combination that lets any of the work get missed by the centre portion.

                  It seems like the intention is to do a shallow cut followed by a deeper cut, although the difference is marginal, anyway.
                  Sure, but then you'll end up with all kinds of weird tooling marks, And you'll end up with a series of vallys and hills if you face a peice in multiple passes.

                  If the tip is low insted, Only it ever cuts (except in the heavyest of cuts, And even then, its only cutting feed per tooth deep), Yet you get a flat surface (assuming tram is good)
                  And generaly if one observes tooling marks, Only the tip of the tool leaves any marks, Iv never seen 'smaller' marks inside a larger mark, Except when tram is spot on, And you get that interfearance pattren beween the front and back tool marks, but even then its clear only the tip of the tool left marks.

                  I wonder if those endmills have a concave face (From the factory), to correct for the apparent convex height of the cutting edges
                  Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                  • #10
                    Originally posted by strokersix
                    There should be end relief towards the center axis so the corners are the deepest into the cut.
                    That is why you need 1 degree relief angle towards the center. You want it to run down hill to center you do not want a high spot on the cutting edge. It will cut off the tip and the rest of the cutting edge is not doing much. If you take .250" or .500" or 750" cut on the side the bottom end has enough clearance it doesn't touch. Did I explain that so it make sense?

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                    • #11
                      Originally posted by Black_Moons
                      I find it weird the flute tips are not straight, doesnt that alter the cutting height of the endmill a little? Seems to me it would cut deeper in the center then the outside as the cutting edge recesses back a little. (unless im reading the geometry wrong)
                      Looking at the picture, #3, one would tend to think that it would only be cutting off the ends or tips of the cutting edge, it's kind of an optical ilusion, but keep in mind that all end mills are held in the fixture at the same degree of angle. The cutting edges or flats do angle in to the center by about .002, they are not straight across or flat and that angle is set by the fixture. It has to be the geometry of that one particular cutter. I wish I could remember what it looked like when it was new. That little fixture was only about $30, well worth it as I have more than got my monies worth out of it. The nice thing about it as it has pre set index spots for multiple flute end mills. The more flutes the trickier it gets, did some six flute and a couple 8 flutes but there is no room for error as you could easily nick the cutting edge of the following flute when doing so.

                      I've run into this same odd problem sharpening drill bits before. I had a couple bits that I just couldn't get the ends to look the way they should when all the other drill bits I was doing were fine. I came to the conclusion at the time that it had to be in the twist or helix of the drill. Seems I also remember someone posting about this problem with drill bits going back a year ago or so.

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

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                      • #12
                        Originally posted by strokersix
                        There should be end relief towards the center axis so the corners are the deepest into the cut.
                        Yes you are correct, thats what I was trying to say.

                        I sharpened one by a different method once where there was no relief towards the center and it did a lousy job cutting as it left heavy swirll marks and had a tendancy to walk. That relief angle is very important.

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

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                        • #13
                          would those be chip-breaker flutes?
                          John M...your (un)usual basement dweller

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                          • #14
                            Originally posted by Deja Vu
                            would those be chip-breaker flutes?
                            I never heard of chip breaker flutes. Milling doesn't stream like turning.

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

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                            • #15
                              Those jigs have a tilt on them so the centre is depressed and doesn't rub.

                              This is how it should be but unfortunately the jigs are made with too much centre relief. They do work but they put too much work / load / pressure onto the tips.
                              To work correctly they need to have the side tilt angle reduced to about 1 degree.

                              I have one here that has been modified and it works a lot better than it did before.
                              .

                              Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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