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Thread: Thread size for QCTP

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  1. #1
    Join Date
    Sep 2007
    West Chester PA

    Default Thread size for QCTP


    I machined a new piece of steel for the QCTP. Basically it is the piece of metal that slides into the compound and then the tools stud is screwed into it.

    This is the QCTP that I have.

    Does anybody know the TPI for this stud ? It measures M14, which I don't have. I bought a cheap tapping kit, and it only goes up to M12.

    Enco lists M14x1, M14x1.25, M14x1.5, and M14x2 ? I am guessing it is either M14x1.25 or M14x1.5

    Any help would be appreciated.


  2. #2
    Join Date
    Mar 2004
    Lansing, Mi, USA area

    Default M14 thds

    The info I have lists M14x2 for coarse, M14x1.5 for fine.
    Russ H.
    editted to correct coarse/fine error, guess which system I use!
    Last edited by Russ H; 10-15-2007 at 05:01 AM.

  3. #3
    Join Date
    Jul 2005
    N W La.


    I dont know the MM thread size ---- I remember it was almost identical to 9/6-18........

    But I'll suggest an alternate solution----this is what I came up with,--- so I would never lose the wrench to reposition the bit again! Used my new (at the time) lathe to make the handle-- threaded it 9/16-18 and used a piece of all thread and made the plate youre talking about with 9/16-18 threads.

    Solved another "lost wrench" problem by making another couple handles to move the compound with out a wrench

    If everything seems to be going well, you have obviously overlooked something........

  4. #4
    Join Date
    Jan 2003



    If you are unsure of the thread, take the bolt down to True Value Hardware or Ace Hardware and test it with their supply of metric bolts/nuts. That way you'll know for sure. They also sell fairly good drill bits and taps so you'll be set to go.

    By the way, if you can afford the time, order a good HSS tap thru one of the machining tool catalogues - they're worth it in the long run. Ace or True Value Hardware stores only sell tools steel taps and dies - at least that's the case in my area.
    Last edited by Mike Burdick; 10-14-2007 at 01:20 PM.

  5. #5
    Join Date
    May 2002
    SE Texas


    I'm not familiar with that brand, but all you have to do is measure the stud. I assume you do not have a metric thread gauge, or you would have done so already. So a workaround is called for.

    If you have an English thread gauge, then you could find the closest thread on it. Here's some close translations:

    M1 ~= 24 or 26 TPI
    M1.25 ~= 20 TPI
    M1.5 ~= 16 or 18 TPI
    M2 ~= 12 or 13 TPI

    The formula for this is:

    English TPI = 25.4 / Metric Pitch

    The match will not be exact as all of the above is approximate, but if they did use one of the above pitches, you should see only about a half to 3/4 thread mismatch over the distance covered by the thread gauge.

    If you don't have an English thread gauge, then use a ruller, preferably a metric one. Lay the stud against the ruller and align a thread peak with a major division. Now count the threads for one centimeter (10 mm). Here's the translation:

    10 threads in 10mm = M1
    8 threads in 10mm = M1.25
    6.66 threads in 10mm = M1.5
    5.7 threads in 10mm = M1.75
    5 threads in 10mm = M2

    The equation for this is:

    10mm / thread count in 10mm = Metric Pitch

    Either of the above methods should get you the correct number if a standard metric thread was used. Of course it is always possible that your thread is non standard.

    A complete set of translation tables could be made up with either of the above methods. But thread gauges are cheap and I would highly recommend getting them.

    Once you know the size, get a good tap set. And be sure to use the correct tap drill. It will surely be specified in mm. Or use the rule of thumb:

    Tap Drill = Major Diameter - Pitch

    Example for 12 X M1: Tap Drill = 12mm - 1mm = 11mm

    If you don't have metric drills, you can translate the metric specified size to English with:

    English diameter = Metric diameter in mm / 25.4
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

  6. #6
    Join Date
    Sep 2007
    West Chester PA


    Thanks for the tips guys. I checked locally and everyone only seems to have
    12 MM as the largest tap. I was going to order just the 14 MM tap but was not sure of the TPI. I was trying to avoid buying a tap set right now, as I have been spending a lot on my hobby lately. Also, I am saving my $$$$ to buy a rotary table next !

    I'll use a metric ruler and figure out the correct tap that way.


  7. #7
    Join Date
    Apr 2006
    Banbury England


    Count 10 threads and meaure length, then divide by ten for pitch.

    If ten threads measuses 15mm pitch is 1.5mm

    Steve Larner

  8. #8
    Join Date
    Nov 2002

    Default Lathe tool post mods

    Not to steal this thread, would like to comment on the picture that Bill Pace put up.

    This is good work. It gives me a couple of ideas.

    I do like the fact that you drilled and tapped all the holes to mount things to the cross slide.

    On the tool post holder on my lathe I drilled and tapped the mounting plate for a set screw so the post would not turn. Until I did this, it would unscrew itself now and then.

    Thanks for the tips.


  9. #9
    Join Date
    Aug 2005
    shreveport La


    Buy your self a metric thread pitch gage only a few dollars . You will need it again.

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