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  1. #1
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    Default HSS Boring bar geometry

    HI all I'd like to grind a boring bar out of a single HSS piece but I can't find any good images of the required geometry. Does anyone have a good link? I will be boring aluminium so positive rake I guess.

    There are plenty of course of right and left hand turning tools.

  2. #2
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    Quote Originally Posted by j3dprints View Post
    HI all I'd like to grind a boring bar out of a single HSS piece but I can't find any good images of the required geometry. Does anyone have a good link? I will be boring aluminium so positive rake I guess.

    There are plenty of course of right and left hand turning tools.
    Hi J3d, Guys,

    The big problem with making an all HSS boring bar is the amount of material that you are going to loose, unless it only a very small one. I've made small boring bars out of HSS rod intended to be used in small diameter holes 10 mm in diameter. Anything smaller and I make a "D" bit, though having said that I've made "D" bits 22 mm in diameter.

    My preference would be to use a piece of round bar that will go into the bore that you want and make a cutting tip from a broken drill or cutter and fasten it using a grub screw in the bar end. You can then grind any profile that you want to make your cutter.

    The hardest part would be drilling the cross hole after you have drilled and threaded the bar end for a grub screw. You have to go careful when doing the cross hole to prevent the drill grabbing and breaking as it cuts into the threaded hole.

    HTH.
    Best Regards:
    Baron J.

  3. #3
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    Quote Originally Posted by j3dprints View Post
    I will be boring aluminium...
    In that case it doesn't have to be HSS. I made a boring tool from O1 steel. You can turn down the shank, leaving a larger radius piece on the cutting end. Grind away most of the waste at the tip to get the desired shape, heat treat and temper to straw colour. Finish grinding and honing in the hardened state.

    In terms of the geometry, I didn't get too scientific. The front clearance angle needs to be more severe as the diameter of the hole decreases. You can rotate in the tool in the holder slightly to change the effective back rake.
    Chris

  4. #4
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    Here's a commercial solid carbide boring tool to give you an idea of geometry.
    Attached Images Attached Images
    Chris

  5. #5
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    Round HSS + round bar as big as you can get away with (= more rigidity). Grub screw for light-duty work or braze for heavy-duty work.

    Quote Originally Posted by BaronJ View Post
    The hardest part would be drilling the cross hole after you have drilled and threaded the bar end for a grub screw. You have to go careful when doing the cross hole to prevent the drill grabbing and breaking as it cuts into the threaded hole.
    Easier to drill the cross hole first.

  6. #6
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    We don't know what diameter hole the OP wants to bore. It may be too small for a boring bar with and inserted cutting tool. I assume that's why he wants to grind it from a single piece of HSS.
    Chris

  7. #7
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    A boring bar cutting edge is in essence a LH cutting tool so I always use the same geometry as I would for a LH cutting tool.

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    Quote Originally Posted by jack620 View Post
    It may be too small for a boring bar with and inserted cutting tool.
    No such thing, just might not be cost effective

  9. #9
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    Quote Originally Posted by elanjacobs View Post
    No such thing, just might not be cost effective
    True, but I was referring to the home made version the other guys were suggesting. Poor wording on my part.
    Chris

  10. #10
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    Quote Originally Posted by Edd View Post
    Round HSS + round bar as big as you can get away with (= more rigidity). Grub screw for light-duty work or braze for heavy-duty work.



    Easier to drill the cross hole first.
    Hi Edd,

    Yes I agree ! Either way the drill can still grab !
    Best Regards:
    Baron J.

  11. #11
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    Quote Originally Posted by jack620 View Post
    We don't know what diameter hole the OP wants to bore. It may be too small for a boring bar with and inserted cutting tool. I assume that's why he wants to grind it from a single piece of HSS.
    Hi Chris, Guys,

    That is why I mentioned "D" bits. In fact when I saw your first picture, I thought it was a "D" bit.
    Best Regards:
    Baron J.

  12. #12
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    Quote Originally Posted by familyguy View Post
    A boring bar cutting edge is in essence a LH cutting tool so I always use the same geometry as I would for a LH cutting tool.
    Thanks, yes this is what I was thinking!

    I was hoping to make it out of 1 piece as I don't have a mill at the current location I have a lathe at.

    The hole I will initially be boring is 30mm but I was also just interested in angles in general.

  13. #13
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    Quote Originally Posted by j3dprints View Post
    The hole I will initially be boring is 30mm but I was also just interested in angles in general.
    I know it's nice to be able to make tools yourself, but I firmly believe that the age of using HSS for general machining has long gone. If you were boring small holes that need expensive fancy holders and inserts then it makes sense, but a cheap insert boring bar set will outperform HSS pretty much every time and you can get down to about 10.5mm bore with an 8mm bar.

  14. #14
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    Quote Originally Posted by j3dprints View Post
    Thanks, yes this is what I was thinking!

    I was hoping to make it out of 1 piece as I don't have a mill at the current location I have a lathe at.

    The hole I will initially be boring is 30mm but I was also just interested in angles in general.
    A 30 mm diameter hole ! That's enormous. I have a very old 1/2" square forged boring bar that would do that easily. It will just fit into a 20 mm hole.

    15-09-2018-001.jpg 15-09-2018-006.JPG

    A 30 mm hole in 1" inch thick EN1 flat bar. This picture is from when I made my Norman tool posts.
    I can't find the picture with the boring bar at the moment.
    Best Regards:
    Baron J.

  15. #15
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    Default Bars

    The big enemy of boring bars is flexing. If you are making your own bars don't use something like mild steel unless it's a large bar of solid proportions. Try to use tool geometries that lessen the stresses on the cutting edge , this is easier said than done.

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