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  1. #1
    Join Date
    Dec 2007
    Location
    Adelaide
    Posts
    172

    Default Very Small Boring bars

    Having just finished another stage of my current project I wanted a break so I decided now is the time to make a small boring bar, I have the usual asian indexable carbide boring bars a total of 5 from 6mm up to 16mm plus a few home brew types that carry a HSS bit secured with a grub screw, but nothing below 6mm and by small I mean one able to parallel bore a drilled hole down to 0.150" diam.

    I recall seeing a youtube video made by Stefan Gotteswinter where he shows some of his diy boring bars so I decided to copy his setup, the boring bar shown started out as length of 0.125" diam HSS, The pic also shows the holder which as made from 12mm MS by off setting it in the 3 jaw (a piece of shim under one of the jaws). I spent about 15min with my Quorn T&C grinder grinding the clearances - the resulting tool has a reach of just over 0.5" - this might not seem like much but as the necked down section of the shank is just over 0.09" diam. I did not want to make it longer thinking it may flex too much. I gave it a try, cuts need to be very small only 1-2 thou and the feed also needs to be VERY slow otherwise tool spring results in a bell mouthed hole, starting with a 3/16" (0.187") hole I was able to bore a 0.193" diam hole in 1020 MS, a No. 11 drill shank was a push fit and made a nice pop sound when pulled out . Resharpening is very easy I only need to grind the end face at the approx correct angle.

    20190810_154235.jpg

  2. #2
    Join Date
    Sep 2012
    Location
    North Yorkshire UK
    Posts
    2,530

    Default

    Hi FamilyGuy,

    I would give serious consideration to "D" bits for boring small holes !

    Fine boring bars are Ok but very delicate. As you say one or two thou cuts plus an unknown amount of spring which will get worse as the tool becomes less sharp.
    Best Regards:
    Baron J.

  3. #3
    Join Date
    Dec 2007
    Location
    Adelaide
    Posts
    172

    Default

    While I haven't ever made a D bit drill I have made and used D bit reamers before and they do work quite well and certainly have their place, things do come up though that don't warrant the time taken to make such a reamer, a small hole may need to be opened up by only a few thou. and the next sized drill is too big. It was the need for a special thick washer that started me thinking about small boring bars.

  4. #4
    Join Date
    Sep 2012
    Location
    North Yorkshire UK
    Posts
    2,530

    Default

    Hi FamilyGuy,

    Yes I know what you mean ! I've fallen foul of that problem a few times. A standard washer is either too small or too big, particularly if it has to fit into a recess.
    Best Regards:
    Baron J.

  5. #5
    Join Date
    Sep 2008
    Location
    Riddells Creek, Vic.
    Posts
    472

    Default

    These little boring tools can be very handy, I just recently used the one that I made years ago to profile the inside of some Delrin spherical washers. I just use broken #1 center drills for the cutting tools.

    Attachment 381239Small Boring Bar 2.JPG

    IMG_1436.JPG
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