Tek-Tips is the largest IT community on the Internet today!

Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!

Register Log in
  • Congratulations TugboatEng on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Search results for query: *

  1. Jacob Cheverie

    Basic GD&T Concept Question

    3DDave - I don't believe one can freely choose the plane in which circularity is evaluated. The cutting plane in which circularity is evaluated is defined to be perpendicular to the (tangent-continuous) spine of the feature. The spine of the feature is the derived median line, obtained by taking...
  2. Jacob Cheverie

    Circularity - measurement with caliper or micrometer

    One reason why that method is invalid: A two point local size check will never be able to detect a tri-lobe form error.
  3. Jacob Cheverie

    Position of an angled hole - Datum Reference Frame questions.

    Please see the attached drawing that I quickly made. I am working on a component with similar geometry and I would like some feedback on a few questions. 1. The position of the Ø.750 hole references primary datum C and secondary datum B. This datum reference frame fully constrains all 6 degrees...
  4. Jacob Cheverie

    Surface Roughness - Filter Wavelength not equal to cutoff length.

    Everywhere I've seen states that the wavelength of the filter is equal to the sampling length. Is this a firm requirement? We are measuring spherical surfaces and we can't quite get the amount of surface measured that we would need to use the filter that matches the roughness requirement. My...
  5. Jacob Cheverie

    Two Datum Features, Single Datum Axis.

    ASHWA, Refer to ASME Y14.5-2018 Para. 7.11.6. Also, please see the edit that I made to my last post. There is a subtle detail in the image. If there were a form tolerance applied at MMC, MMB would be MMC size minus the form tolerance.
  6. Jacob Cheverie

    Two Datum Features, Single Datum Axis.

    The 8x counterbore pattern is controlled with a position specification in which the datum reference frame is simply [C(M)]. In this case, the MMB of datum feature C is simply the MMC size (Ø6.3) because there are no datum references of higher precedence in the DRF, and there is no form tolerance...
  7. Jacob Cheverie

    Two Datum Features, Single Datum Axis.

    It seems like there are a handful of similar examples that can demonstrate this strange situation. You make a good point, Evan, in that a part conforming to a datum structure at RMB should conform when there are MMB/LMB modifiers invoked. That logic seems to imply that datum feature B should not...
  8. Jacob Cheverie

    Two Datum Features, Single Datum Axis.

    I agree in that the secondary datum becoming responsible for the constraint is not a firm requirement but rather a possibility. Another example/argument that may help would be if we were to look at 4-21 (a) with only the left and right holes (as drawn). Starting at the case of 4-21 (d), assume...
  9. Jacob Cheverie

    Two Datum Features, Single Datum Axis.

    ASHWA, You are correct in that the MMB will be Ø16.71. It isn’t so much that deviation from MMC will allow “shift”, but rather once the two surfaces making up datum feature A are measured, they are allowed any available “shift” (together) within the Ø16.71 boundary. For example, the first...
  10. Jacob Cheverie

    Two Datum Features, Single Datum Axis.

    ASHWA, Of the six available degrees of freedom (DOF), it's easier to mention which DOF a cylindrical primary datum feature does not constrain. It does not constrain rotation about it's own axis (1 DOF) and it does not constrain translation along it's own axis (1 DOF). All other DOF are...
  11. Jacob Cheverie

    Two Datum Features, Single Datum Axis.

    The primary datum A constrains two rotational and two translational degrees of freedom. Referencing A at MMB will allow for a relaxation in those constraints such that some amount of rotation and translation is allowed between the datum feature and the MMB. The rotation/translation will allow...
  12. Jacob Cheverie

    ASME Y14.45 Public Review and Comment Period - July 24th to September 20th, 2020

    SeasonLee, I would assume that the rejection of the surface profile characteristic is due to the unequally disposed tolerance zone. A deviation of 0.3 is allowed in the external direction, yet 0.32 was measured.
  13. Jacob Cheverie

    Converting +/- tolerance to a profile tolerance.

    drawoh, That's a good way of putting it. Unfortunately it isn't my design and I was asked to inspect, so I am considering an alternative proposal without knowing what is to be accomplished entirely (other than the +/- implications). The center of the radius is in fact being dimensioned from the...
  14. Jacob Cheverie

    Converting +/- tolerance to a profile tolerance.

    Burunduk, I think that is a good suggestion. With the second tolerance zone being of width 2c, I must determine the size of the first tolerance zone which will be related to the spherical datum feature in an attempt to control the position. Wouldn't the profile control simply be controlling...
  15. Jacob Cheverie

    Converting +/- tolerance to a profile tolerance.

    I have attached a basic image of the situation that I am faced with. There is a sphere and a swept (toroidal) radius. The distance from the sphere center to the radius center has a +/- tolerance. The size of the radius has a +/- tolerance. I'd like to convert this to a profile tolerance, if...
  16. Jacob Cheverie

    Profile Basic Dimensions

    Thank you Burunduk, I also agree that the second method is more direct. Unfortunately, I was the one to propose the first method. Then again, I am not a designer so I am glad to hear that it is equally valid. When speaking to the designer about this part, they also brought up the issue of the...
  17. Jacob Cheverie

    Profile Basic Dimensions

    I have attached an image of a particular situation that I am wondering about. As can be seen, there is a profile of a surface tolerance on a small arc with respect to datum features B and A. My question is in the validity of the current dimensioning scheme. The profile is from point X to point...
  18. Jacob Cheverie

    True Position GD&T

    Burunduk, Not at all. That was just an example. You could take as many cross sectional measurements as you'd like. My point is the resulting best fit line will be used as an axis that will determine your positional error when projected, or continued, over the length of the feature.
  19. Jacob Cheverie

    True Position GD&T

    Typically, the (x, y) coordinates that are reported would be the Z-level where the positional error is the worst (Y14.45 draft backs that up, I believe). Most of the time that is where the axis is projected to intersect with either end of the feature. If I have a 3" bore and I measure a cross...
  20. Jacob Cheverie

    Projection Error When Evaluating True Position of Threaded Hole Far away from Primary Datum

    ktnorberg, As soon as you rotate your coordinate system, you violate the datum reference frame and are thus no longer reporting what you are being asked to report. There is a nominal location and orientation for the hole. It is nominally perpendicular to A, .xxx from B, and .yyy from C. Any...

Part and Inventory Search

Back
Top