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Validate my method is fine please (programmers differ in opinion)

Lord_Warfield
Good Morning Interweb,

So I have a simple alignment. Plane A, circle B, circle C. I Leveled to the plane A and origin Z to it. Translate XY to circle B. Rotate to a line made from B to C. Done.

A different programmer believes I must rotate before translating.... I totally disagree on this simple alignment. Using Legacy btw.

Without being degrading... please reply.


  • I guess you could say the same about the relationship of the startup alignment to the part vs the other method. but i cant convince myself that its a safe bet. not saying your wrong at all.... just my own programming "do not do" list

    Just align everything to PNT31 and the rest will come out just fine.
  • in reply to KronkGitBasher
    You got to love PNT31

    You always LEVEL,ROTATE,ORIGIN or you can have or will have issues depending on the geometry of the part. You can skew the alignment doing it any other way.
  • in reply to cheesiechanman
    Respectfully, the ultimate goal of alignments is to isolate any variation, as-contributed by the part not being squared to the machine's system/components.
    If you level and origin Z first, you prevent introducing bias from vectors being incorrect whilst probing the following alignment features.

    Creating multiple alignments is entirely irrelevant.
    --As long as your final alignment recalls startup, then Levels, Rotates, & Translates all six degrees of freedom per PCDMIS guidance... whatever you programmed before that recall/startup command is the same as not existing in the eyes of the demon.

    Doing your initial align this way enables you to confidently mitigate almost all cosine error from those hits.
  • hear me out. i know this is an exaggeration but consider this... dotted line is the actual part. I need to do more thinking about the entire method. I dont remember where i heard it originally but it vaguely made sense and i have kind of adopted the practice into my programming.

    again... not saying youre wrong or doing anything incorrectly. but hoping i can finally put this to bed for myself. basically my main concern is how much deviation are you removing/introducing by creating multiple alignments vs maintaining the same alignment to measure the features. would be interesting to test this with some gage blocks or something that you could manipulate the positioning of or the angle of the primary or secondary datum to see the deviation contributed if any at all.



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  • I often rely on:

    Measure plane
    - Align: Level and origin Z
    Measure circle 1
    - Align: Recall previous: Origin XY
    Measure circle 2
    Construct line between cir1 - cir2 centroids
    - Align: Recall startup, then Level, Rotate to constructed line, Origin

    Doing this makes sure the rotation vectors that you take for the circles are normal to your component's level plane.
    Also, if your initial origin is perhaps dead-nuts centered between the two circles, you have a chance of flipping vectors as the polarity of your rotation can shift from centroid super easily, and 180 your entire routine.

    I have a similar part.

    I measure a plane and 2 cylinders all in Z+. Create a line from cylinder 1 to cylinder 2.

    I level to the Plane Z+. Datum A
    Rotate to Line Y+ about Z+ Datum C
    X origin cylinder 1. Datum B
    Y origin line
    Z origin plane

    In that order all at once.
  • I always thought that aligning after a feature was more for a progressive style of alignments, Plane, align, Line, align, Point align. I could be wrong.
  • in reply to acgarcia
    that is how it works in the 'quick alignment' option, and many years ago, when people were getting nominals changing in the programs, it was traced back to this method BY TECH SUPPORT, and no matter how many times it was brought up with the code monkeys, they would not change the quick menu alignment method. TECH support proved that you can get nominals changing if you don't have ONE alignment that locks all 6 DOF. It may only happen once in 10 programs or once in 10,000, but ONCE is too many no matter out of however many times.

    You can continue to do that 'progressive' style of alignment, BUT, for safety, the last one MUST control all 6 DOF. Takes only a couple seconds to do, and that is a cheap insurance policy. I do not know if they ever 'fixed' that bug, but I've not heard that they have.
  • in reply to acgarcia
    I always level, rotate, and then origin. I've actually only done plane line point on the test block messing around. I still did level, rotate, origin with that as well. I use cad 99.9% of the time and I wondered if the progressive style would be better to someone without a cad model. idk.
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