Hardinge threading with a partial profile bit. How to widen bottom to Pitch/4.
Close
Login to Your Account
Likes Likes:  0
Results 1 to 4 of 4
  1. #1
    Join Date
    Mar 2009
    Country
    UNITED STATES
    State/Province
    California
    Posts
    6,607
    Post Thanks / Like
    Likes (Given)
    131
    Likes (Received)
    1275

    Default Hardinge threading with a partial profile bit. How to widen bottom to Pitch/4.

    A partial profile bit I use in a Iscar holder. There is a warning label on the box of ten. Warning about grinding dust.
    I was not aware that these bits are altered with grinding. The coating is removed for one thing.

    11ER A60 K20C INSERT – chpeters.com

    The width of the tip is smaller than the length between two diagonal walls of desired thread. That would be Pitch/4.
    Compound set to 29 degrees.

    How do you widen the bottom of the thread if the bit is something like 1/2 the desired width?

    Do you use some simple trig and move the compound along with the cross slide?

    Or do you set the compound to 90 degrees and plunge straight in with the cross, inching the compound to the left to widen the bottom part of the thread?

    Or grind down the tip to the width (Pitch/4)?

  2. #2
    Join Date
    Oct 2010
    Country
    UNITED STATES
    State/Province
    Oregon
    Posts
    5,879
    Post Thanks / Like
    Likes (Given)
    5887
    Likes (Received)
    2284

    Default

    Generally if you use a partial profile insert, you just live with the deeper root. If thread form is critical, buy a full profile insert for the desired pitch.

    If you want to improvise with what you have on hand, either of your suggestions with the compound would work. I tend to feed straight in when threading, so would probably use your 2nd suggestion.

    I'd recommend against regrinding the insert unless it has no chipbreaker (relatively rare in laydown inserts these days). The warning about grinding dust is just the generic warning about cobalt from grinding carbide. It's not specific to these inserts, their grade or coatings.

  3. #3
    Join Date
    Mar 2009
    Country
    UNITED STATES
    State/Province
    California
    Posts
    6,607
    Post Thanks / Like
    Likes (Given)
    131
    Likes (Received)
    1275

    Default

    I have not altered any insert. They chip or break first...

    Feeding in straight causes two chips and they interfere with each other and mess up the cut. According to Machine Shop Practice by Moltrecht.
    There is a method described in that book about how to clean up the back side of a thread when using the 29 degree method.:

    You have a cross slide reference. Back out the compound .010 to .015 and the next several cuts are made with cross movements to the old cross reference.
    See page 368. In the procedure the reference point is brought in farther on the last cut(s). So the I was thinking if I don't go past the reference point
    the root would be wider by what ever amount I dial in. Backing out .010 would widen the root to (sin 29) x (.010) = .0048. This is the time that backlash
    in screws have to be watched or get some digital readouts.

    In this situation:

    tip is rounded but the width is a little less than .005
    1.25mm thread, pitch = .0492, pitch/4 = .0123
    that's 2.5 as wide as the bit.

    The thread is close to a shoulder on a small piece. The insert holder is what gets in close.

  4. #4
    Join Date
    Oct 2010
    Country
    UNITED STATES
    State/Province
    Oregon
    Posts
    5,879
    Post Thanks / Like
    Likes (Given)
    5887
    Likes (Received)
    2284

    Default

    Quote Originally Posted by rons View Post
    The thread is close to a shoulder on a small piece. The insert holder is what gets in close.
    You might get a hair more clearance for the holder if you went over to either a TopNotch-style or a vertical triangle style of insert. But in that case, I'd just buy the full profile insert for the desired pitch.


Tags for this Thread

Bookmarks

Posting Permissions

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