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  1. #1
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    6,439

    Thumbs up Sharpening a Countersink !

    Hi Guys,

    Quite some time ago I had a need to sharpen a countersink, Today I needed to sharpen another ! Back then I made a jig to hold the countersink while rotating it against the grinding wheel. Today I've modified the jig slightly in order to improve the grinding shape.

    03-08-2020-06.jpg

    This is the sort of countersink I've been sharpening. This one has just been ground using the jig.

    03-08-2020-01.JPG

    This is the setup. The sharpening jig is clamped to the grinder table at the correct angle, in this case 41 degrees.

    03-08-2020-04.jpg 03-08-2020-03.jpg

    The workpiece is held in a drill chuck and rotated through 360 degrees.

    03-08-2020-05.JPG 03-08-2020-07.JPG 03-08-2020-08.jpg

    It isn't always realised that the countersinks are not actually round but are tapered cones. The countersink is fed forward into the grinding wheel by a thread. In this case a 1.25 mm pitch screw moving the whole countersink, chuck and shaft forwards as the chuck is rotated.

    This gives the countersink a smooth tapered cone and a sharp cutting edge. The cone providing relief behind the cutting edge in a similar manner to a lathe tool.
    Best Regards:
    Baron J.

  2. #2
    Join Date
    Apr 2012
    Location
    Healesville
    Posts
    2,129

    Default

    I like the thread idea John, at the moment I am making a tool grinding/radius grinding jig and that would be a handy function to incorporate into it.
    I will give it some thought .......

  3. #3
    Join Date
    Dec 2013
    Age
    56
    Posts
    1,416

    Default

    Nice job, I like the thread arrangement.
    Using Tapatalk

  4. #4
    Join Date
    Oct 2007
    Location
    Alexandra Vic
    Age
    69
    Posts
    654

    Default

    Single or multiple edge countersink, it's not really obvious in the pics. Comments below relate to multiple edge bit.

    With the threaded advance, are you rotating 360 deg, or only less than 180 deg to sharpen and relieve one cutting edge at a time? I'm thinking that a full revolution would leave one cutting edge 0.75mm (a half turn advance of the thread) higher than the other, whereas sharpening one edge then resetting in the chuck should result in a reasonably well matched set of edges.
    I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.

  5. #5
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
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    6,439

    Default

    Quote Originally Posted by malb View Post
    Single or multiple edge countersink, it's not really obvious in the pics. Comments below relate to multiple edge bit.

    With the threaded advance, are you rotating 360 deg, or only less than 180 deg to sharpen and relieve one cutting edge at a time? I'm thinking that a full revolution would leave one cutting edge 0.75mm (a half turn advance of the thread) higher than the other, whereas sharpening one edge then resetting in the chuck should result in a reasonably well matched set of edges.
    Hi Mal,

    Good question ! I've tried both ways. It doesn't seem to make much difference, but I've only done the large 1" and .75" ones and they are only two flute. The small 1/2" three flute countersinks seem to be a more uniform cone with the cutting edge backed off much more. Probably more suited for wood than metal.

    The original intention for this jig was to be able to sharpen the Weldon single hole countersinks and deburring bits that I have, and to be able to sharpen an experimental cone tool that I've made. The idea there to be able to make a number of identical cone shaped holes in aluminium. I did try a cone drill but it just squeals and chatters. Again probably more suited to cutting wood.

    With a Weldon single hole countersink, you would turn the full 360 degrees anyway. If you gauge one (1") you will find that the edge runs back about 20 to 30 thou over the full 360 degrees and less with the smaller ones.
    Best Regards:
    Baron J.

  6. #6
    Join Date
    Nov 2019
    Location
    Brisbane
    Age
    69
    Posts
    452

    Default countersink sharpening

    SAM_0679.jpgSAM_0678.jpgHi Baron J.
    Here are some pics of my Royal Oak form relief grinder cam mechanism. At the top is the setting bar which lock into a slot in the cam carrier. This is just before the roller goes over the cam lobe. At this point the countersink is timed using a square on the table. With cross hole countersinks both the leading and trailing edge of the hole must be vertical and cutting edge about to engage the wheel. All fluted countersinks are similar with the flute edges aligned vertical. I have different cams for each number of flutes. The base has 2 opposing V ways in which a carriage with taper cone wheels run. The lot is encased in elastomeric material to keep the poo out. The radial relief has an adjustable stop so travel can be limited or held to zero.
    The 90 deg lever has 5 pivot points and acts as a mixer for movement. You can alter the % of movement in either axis.
    This machine does excellent work, is as old as me and still in good nick. The yanks make good tools.
    Next weekend, if time permits I'll pic a mockup of using an ER collet chuck in a workhead and a square plate on the side for a cam. Not my idea as I stole it from a home tools site.
    Regards
    BC

  7. #7
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    6,439

    Default

    Hi BC,

    Thanks for the pictures and the explanation of how the Royal Oak, cam mechanism works. The only countersink grinding mechanism that I've seen are the pictures of the one shown in the article that I used to make mine. The original Weldon grinding jig used stepped cams to push the toolbit into the grinding wheel and had to be set up for each size. Using a coarse thread to provide a forward movement was simply to avoid the difficulty of making stepped cams, in addition there was no method of indexing to obtain repeatability if you were grinding two or more flute ones.

    In reality grinding a two flute countersink was more me playing about to try and successfully sharpen one, which I did very nicely, I also sharpened a 1" inch three flute the same way, which I use in a handle for hole deburing. Very effectively I might add.
    Best Regards:
    Baron J.

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