PR 231962 profile interpretation per ansi

huangyhg

profile interpretation per ansi
<< Ken Woodbine  --  05/03/05  20:19:40>>
there is some question about whether we are performing the profile according to ansi y14.5.  The thought is that we should be taking the highest devation and multiplying it by 2 and that is the evaluation.  Can you comment on this?
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<< Changes made by Neil Kay -- 02/20/09  13:14:48>>
Status:  RESOLVED to CLOSED
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<< Wade Burton  --  11/02/05  18:11:53>>
The confusion has come because in the newer 2004 ISO 1101 standard, it defines the tolerance zone differently than the 1983 version.  In that case, when fixing the location with a datum, it does define it like this.  So we have already created an option in the registry, in the Option section called UseISOCalculations.  This value defaults to be 0, but when this value is 1, it will apply the deviation like this.  However, a difference here is that with the ISO standard, although it doesn't call it form and location, when its location is fixed, there is only one tolerance value, which we will use the plus tolerance.  The minus tolerance doesn't get applied, like it clearly can in the ASME Y14.5 version.  This was added last week to V4.0.
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<< Changes made by Wade Burton -- 11/02/05  18:12:08>>
Action:  Wade Burton to Ken Woodbine, Status:  OPEN to RESOLVED
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<< Don Turcotte  --  11/02/05  13:16:41>>
Wade, this goes along with the difference between ANSI and ISO which I believe that you are addressing.
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<< Changes made by Don Turcotte -- 11/02/05  13:16:49>>
Action:  Don Turcotte to Wade Burton
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<< Ken Woodbine  --  06/20/05  14:14:54>>
OK, who is the expert to comment on this ongoing debate / confusion?  Is it Don Turcotte?  Someone needs to be unequivical and committ to a stand.
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<< Changes made by Ken Woodbine -- 06/20/05  14:15:12>>
Action:  Ken Woodbine to Don Turcotte
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<< Guillermo Nevado  --  06/10/05  13:31:00>>
Everyone keeps getting this confused.  Especially users that have prior CMM software experience from competitor and legacy (ours) software perspectives.
In a traditional way, everyone looks at profile as the combined effects of form and location.  We provide buttons in the interface to this effect, but this tends to confuse people as they go .. what?.  The standard way is to choose Form and Location always as a default.
If the drawing specifies a bilateral band (where we have a +/- half the tolerance shown in the drawing, the pass fail just about always will be the same as taking the largest deviation (whether positive or negative side), doubling it, and then comparing it to the tolerance band.  Which is Ken's first comment.  Although, this may be confusing to some, the fact is that most softwares (CMM) require the entry of a single  value for the bilateral case (kind of like with true-position).  There is no negative tolerance entry.  Thus, the only way to evaluate the pass/fail, is that you take the absolute value of the largest deviation, double it and compare it to the tolerance (which is already a full band width).
In PCDMIS, we enter a plus and a minus value as half the band.  Therefore, we must look for the largest deviation for either side of the nominal curve.  Which is what I believe we do now but report confusingly as we have MAX, MIN and DEV values.
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<< Dan Zwick  --  05/11/05  12:28:58>>
Y14.5.1M  supports what Scott says:
"For a given point P_N on the nominal surface there is a unit vector N normal to the nominal surface whose positive direction is arbitrary; it may point either into or out of the material. A profile tolerance t consists of the sum of two intermediate tolerances, t+ and t-. The intermediate tolerances t+ and t- represent the amount of tolerance to be disposed in the positive and negative directions of the surface normal N, respectively, at P_N. For unilateral profile tolerances either t+ or t- equals zero. t+ and t- are always non-negative numbers."
"For both unilateral and bilateral profile tolerances two actual values are necessarily calculated: one for surface variations in the positive direction and one for the negative direction. For each direction, the actual value of profile is the smallest intermediate tolerance to which the surface conforms."
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<< Scott Worden  --  05/11/05  12:43:28>>
Multiply by 2 is incorrect.
The actual profile calculation is an ADDITION of the maximum error on one side of the nominal profile plus the maximum error on the other side of the nominal profile.  It's similar to a calculation of circularity on a circle but would actually give the same result as circular runout since position is also considered.  A Profile tolerance is basically a band of a fixed width on a surface condition.
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<< Changes made by Scott Worden -- 05/11/05  12:43:34>>
Action:  Don Turcotte to Ken Woodbine
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