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Thread: Newbie needs help with mini-lathe

  1. #11
    Join Date
    Oct 2013
    Location
    USA MD 21030
    Posts
    5,233

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    Welcome to the HSM gang!

    Here are some video clips showing my experience machining brass. Might give you some ideas:

    http://enginuitysystems.com/pix/Slee...tting_1817.AVI (Turning 59 MB)

    http://enginuitysystems.com/pix/Slee...tting_1818.AVI (Turning - light cut 81 MB)

    http://enginuitysystems.com/pix/Slee...tting_1821.AVI (Grooving 61 MB)

    This is the part I was making, before final clean-up. It's an air fitting for a Sleep Number bed:



    The plastic male hose fitting from the bed had broken off inside the receptacle on the air hose:






    My lathe is a Harbor Freight 9x20.

  2. #12
    Join Date
    Mar 2005
    Location
    Toronto
    Posts
    10,792

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    Quote Originally Posted by devils4ever View Post
    I'm using pre-ground bits that I've been touching up on my grinder trying to keep the original angles. They are all positive angles. I guess it is pre-ground for steel?
    steel, Al, really anything but brass. no coolant needed with 360. Just take a blank and grind some side and front clearance on it (leave the top flat). If you just want to get on with what you've got, take one of your tools with positive rake and stone the top of the cutting edge flat, doesn't need to be very much to stop the digging in. btw, all your cutting will benefit from stoning after grinding
    Last edited by Mcgyver; 05-13-2019 at 03:41 PM.
    .

  3. #13
    Join Date
    Apr 2010
    Location
    Central Indiana
    Posts
    27

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    Most of the other guys have covered about all of the good pointers. I would like to add one point not yet covered. Cross slide and compound screw backlash removal before entering the cut.
    There is another little "trick" that is known to work in turning copper and its alloys, and that is to set the cutting edge of the lathe tool a few thou (0.005 to 0.008) above the work center-line, which makes up for tool downward deflection and reduces the clearance just below the cutting edge.
    Harder to take a big bite out of a BigMack or Whopper if your chin is in the way....heh heh
    BTW, Tap Magic doesn't do much for copper and its alloys. Save your money.

    Good Luck,
    Amigo

  4. #14
    Join Date
    Jan 2004
    Location
    Missouri
    Posts
    31,179

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    Anothe +1 for what Cameron said. Flat top tool is best.

    I never have much trouble with speed cutting brass, but maybe the mini-lathe is different. I am sure it is a lot lighter than my 10" Logan.
    1601

    Keep eye on ball.
    Hashim Khan

  5. #15
    Join Date
    Oct 2014
    Posts
    426

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    If you are grinding tool bits you need to hand stone/polish the grinder marks out with a fine hand stone until the grinder marks don't show any more when looking for them with a 5 or 10 power magnification.

  6. #16
    Join Date
    May 2019
    Posts
    13

    Default Pics

    How do I insert pics? I don't have a website.

  7. #17
    Join Date
    Mar 2017
    Location
    central MA
    Posts
    299

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    For brass and bronze the tool should have a 0 degree rake angle on top, and about 10 degrees clearance on the side and end. With a high speed steel tool bit the Cutting Speed should be around 150 feet per minute as a starting point. To convert that number into a spindle speed use the formula [ ( 4 x C.S. ) / dia.]. As an example, if your work piece is 5/8" diameter then the numbers work out to: (4 x 150) / .625 = 960 rpm. Also, the tool nose should be stoned to have a small radius. As a general rule of thumb I usually try to have the tool nose radius equal the feed rate.
    Last edited by tom_d; 05-13-2019 at 05:37 PM.

  8. #18
    Join Date
    Oct 2013
    Location
    USA MD 21030
    Posts
    5,233

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    Quote Originally Posted by devils4ever View Post
    How do I insert pics? I don't have a website.
    Read the posts in the sticky at the top of the forum. You might not (yet) have permission to upload images here, so you might try www.tinypic.com, or imgur, or other hosting service. I would advise not to use Photobucket.

  9. #19
    Join Date
    May 2019
    Posts
    13

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    Yeah, it looks like I can't attach files or post images yet.

    Let's try tinypic.














  10. #20
    Join Date
    Jan 2007
    Location
    Minnesoa
    Posts
    1,382

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    Hi,

    Yeah, pull the stickout of your tool in about 1/2 to start. Then take your tool and turn it 90 degrees to the face of the surface you want to turn. Pushing the cutting edge into the material is going to make getting a good finish more difficult. Then stone a small radius on the "point" of your tool.
    If you think you understand what is going on, you haven't been paying attention.

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