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Thread: ACME thread cutting tool

  1. #1
    Join Date
    Dec 2004
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    157

    Post ACME thread cutting tool

    I'm experimenting with cutting a 3/8-10 ACME LH leadscrew. I can't find any documentation on how to grind the toolbit. "How to run a lathe" gives next to nothing on the bit itself, only a top view showing how to grind it to fit the ACME screw gauge. Anywone have a picture or diagram. One book I saw showed a "skewed" rectangle when looking at the tool from the front.

    Any thoughts on material? I've got a lot of 12L14 laying around. This is a home shop not a business. Screw will be used for a cross slide vice.

    Ken-

  2. #2
    Join Date
    Jun 2002
    Location
    Los Gatos, CA
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    12

    Post

    You can buy carbide inserts that have 3 tips ground for a particular pitch of Acme thread. You can make a holder for the insert without too much trouble. Notice that you need to calculate the helix angle of the thread and tilt the insert so it matches that, otherwise you'll have trouble with relief angles.

  3. #3
    Join Date
    Mar 2001
    Location
    Southern Oregon
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    1,149

    Post

    Ken, have you checked Machinery's hand book? There is some information there, just don't know it it will answer your question.
    Charlie
    Don\'t ask me to do a dam thing, I\'m retired.
    http://home.earthlink.net/~kcprecision/

  4. #4
    Join Date
    May 2003
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    52N 122W Western Kanuckistan
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    Post

    Have a look here about 2/3 down the page.

    http://www.americanmachinetools.com/...se_a_lathe.htm
    Free software for calculating bolt circles and similar: Origin now settable to bottom left! All values positive. Click Here

  5. #5
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    Jan 2003
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    Temple, Tx
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    Post

    I looked at Evan's reference. Pretty good, but the formula for the tip width is wrong. It implies a wider and wider tip with increasing number of threads per inch. This must be a reciprocal relationship, so the factor P should be in the denominator. If it were me, I'd look it up in Handbook.

  6. #6
    Join Date
    Aug 2004
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    Sunny So Cal
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    Post

    Hello, 10 tpi acme has a root width of .03187". JRouche

    Sorry, forgot to give reference and formula.

    Width of the tool point:
    .3707 divided by the number of threads per inch then subtract .0052" for clearance.

    The reference is actually three books:

    1). Screwcutting in the lathe . Workshop prctices series #3. Martin Cleeve

    2). The Amateur's lathe. L.H. Sparey

    3). Advanced machine work. Robert H. Smith

    Now, where the heck is my Machinery's hand book? it must (better be) be down stairs.

    [This message has been edited by JRouche (edited 02-25-2005).]

  7. #7
    Join Date
    Jul 2002
    Posts
    162

    Post

    You need a 29* thread tool gauge. The depth of thread is half the pitch +.10. Grind your tool to fit this tip width and to 29* and you can cut 10 thds. acme.

    [This message has been edited by happy02 (edited 02-26-2005).]

  8. #8
    Join Date
    Jan 2005
    Location
    California
    Posts
    86

    Post

    Tap drill hole for this thread is 3/8- pitch or .275" your tool must be smaller than that to clear coming out . You'll have better luck with a tap.
    Lumpsmith

  9. #9
    Join Date
    Aug 2004
    Location
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    Post

    Almost sounds like the thread for my south bend steady rest fingers? Is that what you are doing.

    I was gonna make a spare set. I got the brass and was gonna make the tap but got busy. Way too many projects on the burner, most are going up in flames. JRouche

  10. #10
    Join Date
    Jan 2005
    Posts
    19

    Post

    Ken,
    When you cut your ACME thread turn your compound so that it is parallel to the leadscrew you are cutting. After you cut the thread to the proper depth and your nut still will not spin on, then crank your compound .001" towards the headstock and make another pass on the leadscrew (sometimes two or three). The reason for this is when you grind the tool bit to cut the ACME thread it has to be ground at a perfect 29deg. Hard to do when you hand grind a tool.

    Yours, Jim

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