Page 1 of 2 12 LastLast
Results 1 to 10 of 19

Thread: relief grind on parting tool

  1. #1
    Join Date
    Apr 2014
    Location
    Ventura,CA.
    Posts
    94

    Default relief grind on parting tool

    Hello all, should a new HSS parting tool be ground before use? It already has back relief but it appears to be flat across the cutting edge. Thanks, Jim

  2. #2
    Join Date
    Aug 2009
    Posts
    5,364

    Default

    I've always used all of my parting blades as the come. As long as the the edge is sharp and it tapers towards the bottom. Some do some don't.
    Occasionally I have to modify one for some special job.

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

  3. #3
    Join Date
    Dec 2007
    Location
    South Wales
    Posts
    6,486

    Default

    In short, yes, it’s better (imho) to leave a pip on stock than part, so a slight angle on the front allows the tool tip to reach centre on the RH side, leaving a pip on the stock, immaterial if your parting hollow I suppose, it seems to reduce the cutting force, and the grab tendency of an old sloppy lathe (mine) I’ve forgot it a few times and watched the part climb the tool ( irritating)
    Carbide tips seem to come already profiled unless you specifically order square ones for grooving ( pays to use the right one, interesting lesson when the part is wrong and a ring doesn’t fit I suppose.
    It just needs a touch of angle, couple of degrees.
    Swarf or chips are more inclined to roll up and exit the gullet than an oblique(is that right?) tool too.
    By enlarge I swear tooling ends up weighing more than the lathe!, somthing like photography, a camera body an 20 lbs of lenses.
    Mark

  4. #4
    Join Date
    Jan 2007
    Location
    Minnesoa
    Posts
    1,214

    Default

    Hi,

    It depends on what you need it to do. Parting tools are either right handed, left handed, or neutral. And with a HSS tool, it's very easy to grind a slight 1 or 2 degree angle or make them flat as needed. Inserted tools are made handed, (hurrah for more inventory!). Though not all insert parting tools offer those choices. I can't recall seeing any 3mm wide inserts being handed for example. Be sure before you buy.

    So grind it to be handed or not. All your choice.
    If you think you understand what is going on, you haven't been paying attention.

  5. #5
    Join Date
    Aug 2009
    Posts
    5,364

    Default

    I've always kept my mine straight across the cutting edge so it's parallel to the work. Any leading edge or point being on the left or right will cause the blade to veer off in that direction, especially if it's a thin blade.

    If you want to part concave or convex that's the way to do it.

    JL......

  6. #6
    Join Date
    Jan 2014
    Posts
    649

    Default

    I've got a parting blades that's getting short fast because I often walk it over the grinder and change the tip depending on which piece I want to retain the pip.
    *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

  7. #7
    Join Date
    Jan 2007
    Location
    Minnesoa
    Posts
    1,214

    Default

    Quote Originally Posted by JoeLee View Post
    I've always kept my mine straight across the cutting edge so it's parallel to the work. Any leading edge or point being on the left or right will cause the blade to veer off in that direction, especially if it's a thin blade.

    If you want to part concave or convex that's the way to do it.

    JL......
    Hi,

    Yep, grinding a slight angle can cause issues with drift, but so does a flat end. Parting tools often drift a bit no matter what. Final desired results will determine whether or not you can tolerate a slight drift. In a production setting, controlling the part that the little pip is on can save a lot of extra work in getting it removed.
    If you think you understand what is going on, you haven't been paying attention.

  8. #8
    Join Date
    Mar 2005
    Location
    Toronto
    Posts
    9,876

    Default

    Quote Originally Posted by JoeLee View Post
    I've always kept my mine straight across the cutting edge so it's parallel to the work. Any leading edge or point being on the left or right will cause the blade to veer off in that direction, especially if it's a thin blade.
    ..
    agreed with a thin blade in a long part off will drift, but a short stubby parting tool ground on the end of a bit of hss won't. All depends what needs doing. I've a little lathe set up for fasteners or whatever needs doing with a turret and on it there's a carefully ground HSS parting tool, leaves a perfect finish and no pip. But mostly I use carbide for parting because of the side clearance it provides. Having no control over tool geometry, don't know how to eliminate the pip on the parted piece. For that matter I rarely get a good enough finish on the parted piece and usually plan to face in any event....which is ok I guess, I'm onsey twoseys not production....when it is short run production it is with the hss custom parting tool and turret lathe set up

    Still not sure what a "back relief" is? OP can you post a pic or sketch?
    Last edited by Mcgyver; 07-11-2018 at 12:11 PM.
    .

  9. #9
    Join Date
    Apr 2014
    Location
    Ventura,CA.
    Posts
    94

    Default

    Sorry, the relief I was talking about is clearance on the leading edge (the cutting edge) The tool I am using is brand new, it has clearance under the cutting edge but appears square with no relief on the front. Thanks to all so far. Jim

  10. #10

    Default

    Quote Originally Posted by Mcgyver View Post
    Still not sure what a "back relief" is? OP can you post a pic or sketch?
    I'm guessing he means top rake. With a straight top on the blade any top rake will be done by the holder. On my QCTP cutoff holder the slot for the blade is indeed cut at a slight angle for a positive cutting angle. I've also sometimes done a tiny notch at the front of blades with a Dremel disk to provide a more positive cutting angle than otherwise and perhaps an encouragement for the chip to roll up well.
    .
    "I am often asked how radio works. Well, you see, wire telegraphy is like a very long cat. You yank his tail in New York and he meows in Los Angeles. Do you understand this? Now, radio is exactly the same, except that there is no cat." : Albert Einstein

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •