Thread Caliper Pitch Gage
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  1. #1
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    Default Thread Caliper Pitch Gage

    I have a 0-25mm thread pitch micrometer. I made caliper attachments that use the same cone and anvils. Not the best for high accuracy as squeezing the calipers can change reading 0.001 or 0.002". But better than nothing for measuring thread pitch from 0 - 5 inch. I much prefer this than using 3 wires and I like mm/inch change with press of a button.

    Anybody know where to buy caliper attachments for measuring thread pitch diameter??

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    Default Thread Caliper for pitch diameter

    attaching picture of pitch diameter caliper attachment
    Attached Thumbnails Attached Thumbnails threadmiccaliper_withanvils70.jpg  

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    If you need better than +- 0.002 and you care about thread form then an
    optical comparator is the way to go. A micrometer or caliper does not show you thread form. The pitch can be right on but the part still have a bad thread.

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    You are putting a lot of leverage on the gibb of the caliper by pinching so far away from the stem. Make sure you hold the jaws closed with fingers on each side of the attachment rather than using the thumbwheel. -Mike

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    Tom,

    You need different anvils for different pitch ranges. Pitch Master (made in USA) makes the set you are looking for. I bought a set from Penn Tool for ID thread. They're OK, but they set in the drawer now 'cause I bought an IPD gage with software. What a tool! Shars tool sells OD pitch mics up to 6" pretty cheap with all anvils included. Works far better than caliper add ons. By the way, for everyones information: IPD gage range is .93 to 18.00" with good accuracy.

    Ray

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    Default Thread Pitch measuring

    Yes the 0-25mm thread pitch micrometer came with 5 different size anvils and cones for measuring thread pitches as course as maybe 8tpi. I just made the caliper adapters to use the 3.49mm shank anvil and cones that came with a $60 pitch micrometer.
    .....yes I have found squeezing and wiggle near anvil and cone end of the caliper jaws helps seat or lock them / align into thread better.
    ......yes I agree thread form is important. The major diameter is smaller than nominal size. (1/2-13 maybe .490-.495 +/-). Often a tight screw loosens as sharp vee peaks get worn down. Sometimes during cutting metal is pushes / formed and major diameter increases so I also keep measuring major diameter when close to pitch diameter. I have a kids toy digital usb microscope $65 that I have used a few times as a poor mans optical comparator.
    ........ the pitchmaster caliper attachment set is expensive. The caliper adapters I made out of aluminum in less than 2 hrs cost me nothing but the time to make. I found when I thought a thread was close and I was only taking 0.001" depth cuts I was still 0.010+ oversize. Just the measuring and getting an ideal how much more I had to go helps save alot of time. Now I can take 0.005" depth cuts (if screw big enough to take it) and get close much faster.
    .......Even with a CNC lathe often when it is done cutting a thread it is 0.005" off and the tool modifier / offset needs adjusting. I found using just a nut as a gage for cutting screw threads was too slow, too easy to overshoot and have a loose /undersize thread.
    ...... Also I guess I am too used to digital. Be able to go mm/inch or zero to a certain size them measure how much the size difference is saves a lot of math errors. I get nice feeling of accomplishment cutting a thread to a pitch diameter tolerance chart and getting it to fit ok, not too tight or loose. On a Leblond lathe cutting metric threads the thread chasing dial does not work. I have to keep leadscrew engaged slow / brake to a stop, backup the cutter for clearance and run in reverse, bring cutter forward ready for next cut. Try doing that an extra 20 times when you do not have too if you can measure.
    ....... I used a digital indicator and magnetic base to measure tool post movement. I found the cross slide and compound slides needed the gibs tightened as it was jumping 0.010", this was not the normal lead screw backlash but the slides being loose from wear over the years. It is amazing how much easier it is now using a digital pitch caliper and a digital indicator and magnetic base to cut threads.


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