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  1. #1
    Join Date
    Feb 2021
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    Australia Brisbane Qld
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    51

    Default Cleaning up surface of internal bores on lathe

    If I make a cylinder that I want to fit inside a bore, and this is not specifically about pistons in blocks , just generally speaking, with my cylindrical rod in the lathe I use a file or sandpaper to clean up the outside diameter of the cylinder prior to attempting a press fit ......but if I have just used an internal boring bar to make a hole , how do I improve , smooth or polish the inside when it痴 tricky to see or get in there ? I知 not stupid enough to stick a finger wrapped in sandpaper inside the bore. I知 aware I値l just get my finger ripped off or broken. I have a very healthy respect for the torque of the machine

  2. #2
    Join Date
    May 2011
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    Murray Bridge S Aust.
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    5,945

    Default

    There are several ways this can be done, using the boring bar with very fine feed, and a radiused cutting edge. Honing as per a car engine hone or a brake cylinder hone, or if it's a small diameter, reaming. Using a tool post grinder is another option, as a last resort as it's a VERY messy operation for the lathe.
    There are others on here that are far better informed than I on this subject.
    Kryn
    To grow old is mandatory, growing up is optional.

  3. #3
    Join Date
    Aug 2010
    Location
    Toorloo Arm, VIC
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    39
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    1,270

    Default

    Piece of dowel with a slit hacksawed in the end, and a piece of sandpaper in the slit that then wraps around the outside?

  4. #4
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
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    Default

    Hi Steve, Guys,

    If you are just going for a press fit, then as Kryn says, use a well rounded tip on your boring bar cutter and a fine feed. You shouldn't need to do anything else.

    If you are going to put a piston in there then as
    Jekyll and Hyde
    Piece of dowel with a slit hacksawed in the end, and a piece of sandpaper in the slit that then wraps around the outside?
    Says. This idea works well for other types of bores as well.
    Best Regards:
    Baron J.

  5. #5
    Join Date
    Feb 2021
    Location
    Australia Brisbane Qld
    Posts
    51

    Default

    I did not know about brake cylinder hones , but after reading about them here, I found a local supplier that offers one between 19-63 mm. That will cover most of what I知 likely to need. Most of my boring bars are insert type but I have a couple of brazed tip units that I can sharpen to a radius tip , and the edge of a reamer could also work , and good old sandpaper wrapped around a stub too .....good tips men, thanks

  6. #6
    Join Date
    Aug 2008
    Location
    Melbourne
    Age
    34
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    1,075

    Default

    You should be able to get perfectly finished bores straight off the tool with the right insert and cutting parameters. What material, speed, feed and cut depth are you using?

  7. #7
    Join Date
    Nov 2017
    Location
    Geelong, Australia
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    57
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    2,651

    Default

    If you池e buying a hone that you think is likely to get a bit of use then make sure that replacement stones are available or that it痴 cheap enough to throw away if they aren稚.
    A hone that will go as small as 19mm will only have small stones so you will wear them out pretty quickly on larger bores.

    Like sandpaper, Scotchbrite or emery cloth in a split arbor also work well if the bore has just been machined and you池e only trying to improve surface finish.

    Steve

  8. #8
    Join Date
    Nov 2019
    Location
    Brisbane
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    Posts
    452

    Default bore finishing

    Hi again.
    A hone will correct out of round and concentricity as well as finish the bore. If you just want to improve the finish I have used pvc tube split at the end and wet and dry. if it is ferrous and 400 grit is fine enough then try alox no fill paper.
    regards
    BC

  9. #9
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
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    Default

    Quote Originally Posted by STEVEMORSE View Post
    I did not know about brake cylinder hones , but after reading about them here, I found a local supplier that offers one between 19-63 mm. That will cover most of what I知 likely to need. Most of my boring bars are insert type but I have a couple of brazed tip units that I can sharpen to a radius tip , and the edge of a reamer could also work , and good old sandpaper wrapped around a stub too .....good tips men, thanks
    Hi Steve,

    The reason a rounded tip works well is because, when you are boring under power, you are actually cutting a very fine thread in the material surface.

    Say you were using 2 thou per turn, then the rounding on the tool tip should be about three times that. The idea is that the rounding is greater than the width of thread produced by the feed and removes them giving a more smooth finish ! Its also more easily lapped/polished when finished if needed.

    HTH.
    Best Regards:
    Baron J.

  10. #10
    Join Date
    Sep 2008
    Location
    Riddells Creek, Vic.
    Posts
    831

    Default

    I wouldn't expect too much from a simple spring loaded brake cylinder hone, they are not designed to remove material like a proper honing mandrel such as a Sunnen etc.

  11. #11
    Join Date
    Aug 2008
    Location
    Melbourne
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    Default

    If it's just to smooth the bore out, rather than to open the bore out to size, a cheapy might do the job.

    Just remember that your bore size WILL grow a little, regardless of how you do it, so it might be prudent to work to the small end of your tolerance range until you determine how much material your hone is removing.

  12. #12
    Join Date
    Aug 2020
    Location
    Cowaramup WA
    Posts
    28

    Default

    For the sake of completeness, there are also available flexible Ball hones which individually suit only a small range of diameters and tend to be expensive.

    It is also relatively easy to make expanding laps to polish bores. They can be purchased, but don't seem to be readily available in Aus, (though I haven't looked too hard.)

    Dave.

  13. #13
    Join Date
    Oct 2004
    Location
    Southern Highlands NSW
    Posts
    1,894

    Default

    I have made some motorcycle small end bronze bushes, finishing freehand with a brake cylinder hone, fine stones.

    An old engineer who used to race bikes taught me this method:
    - Chuck a piece of leaded bronze, face and turn OD to size plus one thou.
    - Still in chuck, bore ID to gudgeon pin size, part off.
    - Press into conrod. The bush ID will decrease by about a thou.
    - Use brake hone with kero, reciprocating, until pin fits nicely.

    This has worked for me every time.
    I don't think I could provide the reciprocating action in a lathe, unless with a special complicated arrangement.

  14. #14
    Join Date
    Dec 2007
    Location
    Adelaide
    Posts
    574

    Default

    I use indexible tip type boring bars and don't have too much trouble getting a good finish, from experience, once I'm within .0015' - .002" of the final size I take another 3 or 4 more cuts at the same setting - finest feed with the cross slide locked - this usually brings it to the correct size, if not then a few more cuts at the same setting - the theory being that you will always get tool spring with a boring bar - the amount will depend on the length and size of the boring bar, so it is best to set the length just enough for the hole depth and use the biggest boring bar that will fit even if it means changing up to a bigger bar as the hole gets bigger. With a bit of experience you get to know how much spring to expect.

  15. #15
    Join Date
    Nov 2007
    Location
    melbourne australia
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    3,228

    Default

    Quote Originally Posted by familyguy View Post
    use the biggest boring bar that will fit even if it means changing up to a bigger bar as the hole gets bigger.
    Great idea. I'd never thought of that.
    Chris

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