No, the graphic doesn't reflect the datum scenario given in the OP. The larger issue, I thought, was the question of using profile to control a cone. As I have some existing models that I use for training & documentation, I decided to use them to illustrate how to verify a conical surface spec'd with a profile control.
The drawing would, indeed, show basic dimensions for the end diameters, the length (unless a FOS, in which case +/- tol could be used), and the included angle.
Verification methodology depends on what you have at hand.
1) runout stand inclined at half the basic included angle by using a sine bar or angle plate; this puts the basic profile to the horizontal (or vertical), and the indicator can then run in a straight line wrt the surface plate.
2) runout stand as shown in graphic, and indicator on an inclined guide rail (picture two vertical stand posts, and two cross rails which remain parallel to each other while skewed to the vertical posts; I haven't seen this one in use, but I have seen the setup). I have also seen a single cross-rail, but don't like it as the indicator can pivot about the cross rail axis, thereby losing its angularity relationship wrt the basic profile geometry.
3) manual optical comparator, with the datum axis aligned horizontally or vertically; you offset the object from the center by the basic radial distance at either end, rotate the crosshairs & grid on the screen to the basic angle, then you can travers +X/-X or +Y/-Y until you get the limit of the surface at that section, or you can use an overlay with the nominal, min & max boundaries and see if the conical surface violates that boundary as you rotate it about the axis
4) an automated profile vision system rotates the workpiece about its datum axis at high rpm, and a light curtain & camera traverse longitudinally along the axis to establish the surface which is then compared electronically to the CAD geometries directly or to a manually entered basic geometry and offset boundaries.
Options #1 & 2 use basic inspection apparatus that should be available in pretty much any shop. This reinforces how easy it can be to verify a surface profile with basic equipment.
Option #3 requires an optical comparator, but that's pretty common in most shops that I've seen. Again, no real challenge with this methodology.
Option #4 requires a comparatively inexpensive piece of equipment which, in a production environment, saves far more on labor costs than its purchase price.
A CMM in scan or point mode can be substituted for an indicator if preferred.
Conical tapers are the bread & butter of the tooling and molding industries. These and other methods are used every day for conical tapers.
As for profile of a surface vs size & circular R/O;
- Profile checks size, form, orientation & location in one setup and inspection process
- size is to be checked by Taylor's Principle (Full form at MMC, 2 pt check at LMC)
- how do you know you got the actual circular cross-section rather than a skewed cross section?
- how will you check form at each point?
- circular runout is a check at each cross-section perpendicular to the datum axis
- what happens between these sections? waviness along the length of the part (as my modeled workpiece) will not be detected by circular runout
- what if you want a large size tolerance, but need good form along the length of the workpiece? Size & Circular Runout can't do this; you'd have to add a straightness control also, but that would only control single longitudinal elements, not the net effect. Would you then add a circularity control as well? Of course not because Form controls are nasty to verify. The alternative is a composite surface profile, and the inspection apparatus would typically be a runout setup.
Now, Marvin is a difficult creature to work with, and he's still tentative about his job, so he's just moving into position. As in reality, there will always be a bit of a cosine error as he can never truly get the deflection probe to a perfectly normal orientation to the basic surface.
Marvin's second indicator is part of his Q2009 Inspection Modulator Probe, complete with aiming reticle & hair-trigger download of digital data. Marvin would not, however, ever use his capabilities for the evil task of verifying concentricity. ;~}
Jim Sykes, P.Eng, GDTP-S
Profile Services
TecEase, Inc.
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