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  1. #1
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    Feb 2006
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    Default Shop made counter bore

    SWMBO is setting up horse agility activities at the agistment property where she at stables her horse. If you know dog agility (dogs racing up and down ramps and around a line of poles etc) you will know what I mean.

    Currently we (or more like "I") am up to setting up a row of 2m high white poles spaced at various distances apart that the horse and rider has to go clockwise around one and then anti-clockwise around the next etc. There are dozens of activities and the more advanced activities involve working with livestock. All the items have to be portable, pack-up-able, and minimal disturbance of turf etc so no just belting sticks into the ground.

    We've settled on short lengths of log for a base and a length of PVC pipe as the pole. Easy enough I thought. Drill a hole in the stump and poke the PVC in.
    The PVC OD I'm using has a 26.6 mm so I tried using a 28 mm bit but the hole is a tad too large and so the poles get a lean on.

    I have an adjustable diameter "bit" for a brace but it's blunt as, and as I'm going into end grain of spotted gum I wanted to use a DP and the bit shank is not compatible with the DP chuck.

    So I whipped up this counter bore from a 120 mm length of BMS.
    IMG_3443.jpg
    The head is 20 mm in diameter and the shank is 16 mm so it suits a 16 mm capacity chuck.
    The cutter is a 26.6mm length of 1/4 HSS held in place by two 6mm grub screws.
    The cutting ends of the HSS was quickly (<5 minutes) shaped on a CBN wheel.

    A 20 mm hole is drilled into the log end and then the counterbore is partially inserted into the hole and then just bore down through the timber.
    IMG_3442.jpg

    Here's the side profile of the cutter.
    IMG_3444.jpg

    Cuts like a knife thru warm butter even in the hard stopped gum.
    If I want a different diameter hole (above 20mm diam of course) all I have to do is cut and shape up a new cutter.

    Here you can see the final idea of the poles.
    The pole on the left is in the 28mm hole and the one on the right is the 26.6mm hole.
    At first glance the one on the right seems worse but use the ribs of the shed sheeting for reference and you will get a better idea of verticality
    Also the pole in the 26.6mm hole is held in very firmly so much so that the stump can be picked up using the PVC pole
    IMG_3440.jpg

    The other thing I have made for the arena is the fake cow.
    This is used to desensitising equestrian horses so they working with stock.
    Eventually it will get a second par of wheels and be moved around a paddock by a winch.
    I can't believe how war the horses are of it when they first see it.
    No I did not paint it. I just dd the wood work.
    SWMBO painted it and made the tail.

    IMG_3435.jpg

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  3. #2
    Join Date
    Nov 2004
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    Millmerran,QLD
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    Default

    "If I want a different diameter hole (above 20mm diam of course) all I have to do is cut and shape up a new cutter."

    Actually you can use the same cutter by extending the cutter up until the grub screw can no longer make contact. The shaft does all the support work in the 20mm hole. I think the metal workers call this a fly cutter.

    Nice job Bob.

    Regard
    Paul
    Bushmiller;

    "Power tends to corrupt. Absolute power corrupts, absolutely!"

  4. #3
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    Default

    Quote Originally Posted by Bushmiller View Post
    "If I want a different diameter hole (above 20mm diam of course) all I have to do is cut and shape up a new cutter."

    Actually you can use the same cutter by extending the cutter up until the grub screw can no longer make contact. The shaft does all the support work in the 20mm hole. I think the metal workers call this a fly cutter.
    Thanks Paul.

    Fly cutters are commonly used in metal working (I was using one of mine just last week - see photo) but are slightly different in that they do not have a supporting stub of metal that enters a predrilled hole in front of the cutter.

    Fly cutters also only usually have a relativley small point of contact at the end or tip of the cutter and are usually used to thin/flatten/smooth metal surfaces. The work pieces are usually moved past the swing or arc of the cutter progressively removing a thin circular arc of material. This is why circular arc patterns are commonly seen on flat portions of machinery and often on WW machines.

    On the setup below, the width of the arc or metal removed depends on the depth but both are usually less than 1/2 mm as you can see by the size of the swarf.
    The diameter of the arc (or size of any hole being cut) is determined by a fine screw in the side of the silver part of the cutter holder in relation to the black section of the holder so incrementally moving the silver part of the holder away from the centre of the black part of the holder will will generate a larger hole. The mill has to be stopped to adjust the fine screw and only sub-mm increases in the hole size can usually be achieved with each adjustment on small mills. On larger mills much greater changes in hole size can be achieved and this is often used to enlarge holes in awkward shaped workpieces or enlarge large holes.

    IMG_3420.jpg


    Counter bore bits in metal working usually look like this and are commonly used to provide a flat bottomed recess for the head of a cap or socket head screw.
    counterbore.jpg


    If the work piece/object can be held in a lathe then a simpler way to enlarge holes in metal is to use a boring bar held in the lathe cross slide tool post. The big advantage being the lathe does not need to be stopped to move the boring bar incrementally away from centre to cut a larger hole.

    In my case I thought a two piece cutter would minimise any wobble brought about by any slight mismatch between the size of the 20mm hole in the timber and the 20mm diameter tip of the counter bore end so as to produce a more accurate size hole which it seems to have done. However, in many other situations a single cutter would usually suffice and I will probably end up making a cutter tip that can be extended as you suggest

  5. #4
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    Default

    Hi Bob
    I assume your PVC is 25 mm ID.
    If so you could have used a 25 mm tenon cutter



    but, I agree -- not as much fun as making your own tool
    regards from Alberta, Canada

    ian

  6. #5
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    Bob

    Your counterbore is reminiscent of a commercial product marketed by Practool under the name of "Superdrill," which is how I knew the cutter could be extended.

    Their tool is primarily intended for cutting holes in metal and starts with a 1/2" hole. It is then enlarged to 1" for holes that size and upwards where the fatter section of the tool becomes the centering device. For larger holes again the large collar is attached to support a longer cutter again.

    It is intended for people without access to large diametre twist bits and every time I have seen it demonstrated it was held by an electric drill supported in a drill press. In other words not a pedestal drill press. I bought mine in the mid eighties I think. I have drilled 2" holes in end grain timber (Grey/White box) 6" deep with it in the past.

    P1040686 (Medium).JPGP1040687 (Medium).JPG

    Regards
    Paul
    Bushmiller;

    "Power tends to corrupt. Absolute power corrupts, absolutely!"

  7. #6
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    Default

    Quote Originally Posted by ian View Post
    Hi Bob
    I assume your PVC is 25 mm ID. If so you could have used a 25 mm tenon cutter
    but, I agree -- not as much fun as making your own tool
    23.2 mm ID

    Quote Originally Posted by Bushmiller View Post
    Bob

    Your counterbore is reminiscent of a commercial product marketed by Practool under the name of "Superdrill," which is how I knew the cutter could be extended.

    Their tool is primarily intended for cutting holes in metal and starts with a 1/2" hole. It is then enlarged to 1" for holes that size and upwards where the fatter section of the tool becomes the centering device. For larger holes again the large collar is attached to support a longer cutter again.

    It is intended for people without access to large diametre twist bits and every time I have seen it demonstrated it was held by an electric drill supported in a drill press. In other words not a pedestal drill press. I bought mine in the mid eighties I think. I have drilled 2" holes in end grain timber (Grey/White box) 6" deep with it in the past.

    P1040686 (Medium).JPGP1040687 (Medium).JPG

    Regards
    Paul
    Thanks Paul, I like the two step cutting capability!

  8. #7
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    May 2011
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    Murray Bridge SA
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    Default

    On the odd occasion that I've needed an odd size hole, I've modified a Forstner bit of the next size up. Mounted it in the drll chuck in the wood lathe, then attacked it with an angle grinder with a flap disc. I rest the grinder on the tool rest to keep it steady.
    Kryn
    To grow old is mandatory, growing up is optional.

  9. #8
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    Kryn

    Depending on the intended use, spade bits are even easier to modify.

    Regards
    Paul
    Bushmiller;

    "Power tends to corrupt. Absolute power corrupts, absolutely!"

  10. #9
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    Default

    Quote Originally Posted by Bushmiller View Post
    "If I want a different diameter hole (above 20mm diam of course) all I have to do is cut and shape up a new cutter."

    Actually you can use the same cutter by extending the cutter up until the grub screw can no longer make contact. The shaft does all the support work in the 20mm hole. I think the metal workers call this a fly cutter. l
    I did this yesterday when I had to cut a 27.5mm hole in a couple of stumps. I learned one thing though - one has to hold the workpiece very firmly when using an uneven side protrusion of the cutter. I did this by screwing a couple of 75mm 14G bugle headed screws into the underside of the workpiece and holding these firmly in the DP vice. This setup tends to overcut the hole size compared to the actual side protrusion of the cutter so one has to do a few practice runs to get the hole size required.

  11. #10
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    Default

    Quote Originally Posted by Bushmiller View Post
    Kryn

    Depending on the intended use, spade bits are even easier to modify.

    Regards
    Paul
    Yes, have done that on many occasions, bit hard to find a 42.5+mm spade bit though.
    DSCF0479.jpg
    This was made using a 46mm hole saw for the inner Hub, the modified Forstner for the Rim, and a 40mm forstner bit made the Clamping Ring.
    Kryn
    To grow old is mandatory, growing up is optional.

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