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Tru-pos (opinion)

Jay_Q
I would like to get some opinions on Tru-pos locators. These are the tapered style that have a no/go thread at the end so it only locates on the thread.

1. is it better practice to project the cylinder back to the surface and report out that circle? Or is Tp perpendicular to centerline using the cylinder better? (I use legacy)

I like perpendicular to centerline method because we measure a lot of parts that are on spherical or conical surfaces. It just seems to add a unnecessary chance on error.
As far as surfaces that are flat and perpendicular I still use the same method.

2. I actually have had good success with checking threaded holes using pitch. But…. What I don’t like is the chance of the probe picking up a chip off of the inside of the thread. Potentially throwing other surfaces or holes to be off.

So, if money wasn’t an object as far as buying tru-pos. What do you all like as far as accuracy?



Parents
  • I would like to get some opinions on Tru-pos locators. These are the tapered style that have a no/go thread at the end so it only locates on the thread.

    1. is it better practice to project the cylinder back to the surface and report out that circle? Or is Tp perpendicular to centerline using the cylinder better? (I use legacy)

    I like perpendicular to centerline method because we measure a lot of parts that are on spherical or conical surfaces. It just seems to add a unnecessary chance on error.
    As far as surfaces that are flat and perpendicular I still use the same method.

    2. I actually have had good success with checking threaded holes using pitch. But…. What I don’t like is the chance of the probe picking up a chip off of the inside of the thread. Potentially throwing other surfaces or holes to be off.

    So, if money wasn’t an object as far as buying tru-pos. What do you all like as far as accuracy?



    1. I have never use a Tru-pos plug on a threaded hole in a 3D contoured surface, but here is how I would probably approach it. If you select an auto circle at the surface of the threaded hole, you can change it from an inner circle to an outer circle and then adjust the diameter and depth for the Tru-pos plug. When the feature is measured it will automatically project the hits to the nominal surface and evaluate the XYZ position to that surface. It wouldn't account for if the hole is crooked relative to the surface because it would project along the nominal vector of the hole, but those plugs are so short that I think that error would be negligible unless the hole is visibly crooked. Though, your idea of measuring a cylinder and just reporting that could help you troubleshoot any issues.

    2. I tend to prefer this method, but I have had issues with it as well. The only thing I can offer is to consider the machining method that is used to put the thread in that hole. If the hole is tapped or thread-formed I think that the pitch method works quite well, burrs and thread profile issues aside. However, If the hole is thread milled it is possible that the threads may not be concentric with the pilot hole that makes the minor diameter of the thread. That is when I like to consider Tru-pos plugs. It's a use your best judgment sort of thing.

    In reality, I tend to just use the pitched hole method and just bring out the Tru-pos plugs as a way to verify the measurement when I don't like the results I'm getting. Rolling eyes
Reply
  • I would like to get some opinions on Tru-pos locators. These are the tapered style that have a no/go thread at the end so it only locates on the thread.

    1. is it better practice to project the cylinder back to the surface and report out that circle? Or is Tp perpendicular to centerline using the cylinder better? (I use legacy)

    I like perpendicular to centerline method because we measure a lot of parts that are on spherical or conical surfaces. It just seems to add a unnecessary chance on error.
    As far as surfaces that are flat and perpendicular I still use the same method.

    2. I actually have had good success with checking threaded holes using pitch. But…. What I don’t like is the chance of the probe picking up a chip off of the inside of the thread. Potentially throwing other surfaces or holes to be off.

    So, if money wasn’t an object as far as buying tru-pos. What do you all like as far as accuracy?



    1. I have never use a Tru-pos plug on a threaded hole in a 3D contoured surface, but here is how I would probably approach it. If you select an auto circle at the surface of the threaded hole, you can change it from an inner circle to an outer circle and then adjust the diameter and depth for the Tru-pos plug. When the feature is measured it will automatically project the hits to the nominal surface and evaluate the XYZ position to that surface. It wouldn't account for if the hole is crooked relative to the surface because it would project along the nominal vector of the hole, but those plugs are so short that I think that error would be negligible unless the hole is visibly crooked. Though, your idea of measuring a cylinder and just reporting that could help you troubleshoot any issues.

    2. I tend to prefer this method, but I have had issues with it as well. The only thing I can offer is to consider the machining method that is used to put the thread in that hole. If the hole is tapped or thread-formed I think that the pitch method works quite well, burrs and thread profile issues aside. However, If the hole is thread milled it is possible that the threads may not be concentric with the pilot hole that makes the minor diameter of the thread. That is when I like to consider Tru-pos plugs. It's a use your best judgment sort of thing.

    In reality, I tend to just use the pitched hole method and just bring out the Tru-pos plugs as a way to verify the measurement when I don't like the results I'm getting. Rolling eyes
Children
  • in reply to Cris_C
    The Tru pos ones stick out pretty far (up to .250”) from the checking surface. That’s why I was wondering if checking a cylinder and projecting a circle back to the surface it’s on is better or if just checking the cylinder with perpendicular to centerline on from the “worst end” would be better. A customer tried telling me it should be projected to the surface. Any thoughts?
  • in reply to Cris_C
    I think that measuring a cylinder and projecting it to the surface would be the most forgiving method from a manufacturing and measuring standpoint. If that is what the customer wants, great!

    Just thinking out loud. When I think of the function of most threaded holes it normally involves fastening one part to another. Where that threaded hole meets the surface is often most important. The assembly of many parts will go together just fine even if a threaded hole is a little crooked (not perpendicular to the surface) just as long as the position is correct at the mating surface (where holes line up). An exception would be if the mating part has a known thickness with a hole that has a fastener going through it. In that case a projected tolerance may be used to defined distance off of the part (often the thickness of the mating part) that is most critical for the threaded hole position. In this case, the customer is saying that the position at the surface is what is most important to them. Good to know.

    I'm not sure how best to do that with Tru-pos plugs measured as a cylinder on a contoured surface. I'm pretty sure you could select the threaded hole as an auto cylinder, change it from an Inner cylinder to an outer cylinder, then adjust your diameter and measuring depths to work with the Tru-Pos plugs. Then, construct a cast circle from that cylinder. I think that would place a circle at the theoretical face of the part with a diameter and vector that matches the cylinder. It's the sort of thing that I think would work, but I wouldn't be sure until I tried it. I'm away from my desk today so I can't test it out. I suspect that the vector of the cylinder may also need to be flipped to make the cast circle go to the face of the part rather than the face of the Tru-pos plug.
  • in reply to Cris_C
    Thanks Cris_C It’s always nice to get opinions on check methods. I like to hear what other people do in the industry and critique my methods here and there if I feel the need to. There are so many ways to achieve the result. Gotta love this forum!
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