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Thread: Boring bar issues

  1. #1
    Join Date
    Jan 2008
    Posts
    141

    Default Boring bar issues

    I do a fair amount of boring on my 11 inch Logan. Job I in it now is 4 inch diameter 3 inch disk. Need 1 1/2 inch one end 2 1/8 other. Started with a small # 2 M/T drill worked up to 3/4 inch then Silver and Demings to 1 1/4. Then go at it with the boring bar to size.

    Bar I am using is a 1 inch, 90 degree one end 45 the other. Run in a QR AXA tool post. 1/4 inch HSS bit, well ground and sharp. Itís solid no chatter.

    Problem is the bits fixing screws. Two Allenís holding the bit. Very small. 2 MM Allen wrench fits it. You canít put much torque on the screws or the head strips. Correct Allen wrench clean with air hose setting up nothing keeping the screw from holding except itís so small. Working out to size the bit will slip unexpectedly, have to shut down and reset. Yesterday gave it up and used carbide tip boring bars instead.

    I see two options, use the bar for light use only, but even light internal threading bit slips itís a problem. Or drill the holes out tap for a larger screw .

    Should I give up on big boring with the bar ?

    Boats

    .

  2. #2
    Join Date
    Jan 2003
    Location
    Atascosa County, Texas
    Posts
    8,155

    Default

    Maybe give up on THAT tool. You give no info except the screw hex size. That must be a very small bit.

  3. #3
    Join Date
    Aug 2009
    Posts
    6,553

    Default

    It just sounds like a poorly designed tool. If you could modify the bar, ..... like larger set screws or some type of clamp it may be salvageable and less aggravating to use.

    I have a set of 3/8" tool holders that take a 1/4" IC insert. They came with a really small Torx type hold down screw. Couldn't really tighten it down with out stripping the head and removing it was the same problem.
    Finally I found some stainless slotted flat head screws that fit and I replaced all the Torx screws. Haven't had an issue since. Perhaps you could find some replacement screws.

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

  4. #4
    Join Date
    Aug 2010
    Location
    Victoria BC
    Posts
    889

    Default

    Or a duct tape baling wire definitely not long term solution might be thread locking compound.
    "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

  5. #5
    Join Date
    Dec 2015
    Location
    Chilliwack, BC, Canada
    Posts
    5,571

    Default

    Using TWO setscrews to me suggests that the cutting tip is a piece of HSS rather than a carbide insert. If so I don't see any reason not to drill out and thread for bigger screws to allow using a bigger hex wrench.

  6. #6
    Join Date
    Dec 2016
    Location
    Helsinki, Finland, Europe
    Posts
    3,597

    Default

    I have never understood the desire to use some teeny-weeny setscrews in boring bars to hold the tool bit. I have built my own diy boring bars so that I have used M4 socket head at minimum. Might need splitted bar or some sort of wedge but 1” bar leaves plenty of room for design.

  7. #7
    Join Date
    Jul 2001
    Location
    Green Bay, WI
    Posts
    3,584

    Default

    Two things:
    I think your problem may be the quality of the screws.
    USA made HSSS (Hex Socket Set Screws) can only be made to US Standards (ASA 1962 ie) , while foreign screws (You said metric!) "CAN" have
    lower standards. There is a huge difference in strength. If you use foreign made screws, only get DIN 12.9 which is comparable to ASA 1962
    . Obviously American made or DIN 12.9 are more expensive. Look for Unbrako,CamCarr,Allen or HK (HoloKrome)
    Second thing
    Trying to tighten a screw against a highly polished surface (HSS Toolbit) can be like slipping on ice, so you need a rougher surface.
    Take the top or surface of the toolbit (where ever the screw impinges) and touch it lightly on a FINE grinding wheel to get a satin type finish to allow the screw a grip on the toolbit.
    Rich
    Last edited by Rich Carlstedt; 08-04-2019 at 10:32 AM.

  8. #8
    Join Date
    Oct 2012
    Location
    San Antonio TX, USA
    Posts
    2,767

    Default

    I'd make it into a split clamp and use the biggest screw I could find - that's if the hole branched for the bit is a close fit. Another option might be to put another set screw in 90deg around the bit from the others. If the two are coming in from the top, put the third in from the front of the bar. Or make an insert to go at the back end of the bit with another set screw as a backstop/ pusher. Plus make the other screws bigger

  9. #9
    Join Date
    Jul 2014
    Location
    Southern Indiana
    Posts
    495

    Default

    Boats: Is the pocket worn? Is the pocket high in the center? Good luck.

    Sarge41

  10. #10
    Join Date
    Jan 2008
    Posts
    141

    Default

    Some good tips. No doubt the small screws are Chinese Junk, for sure I am going to drill out and tap for at least 1/8 inch quality American made Allen’s, roughen up flats on the 1/4=inch HSS Bit good idea too. The pocket is tight no issue there.

    Have to go any further to made it work will send it to the scrap box & start from scratch. I really prefer boring with a bit I have ground from HSS. The Chinese carbide tipped bars work but don’t leave the finish I want most times & grinding myself can use the same bar for threading

    Thanks all

    Boats
    Last edited by boats; 08-04-2019 at 12:06 PM.

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