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Alignment Question

Lukas
Hello. I am trying to better understand how alignments work. For example the advantages of doing multiple alignments vs one single alignment, rotating before translating, etc.

If you don't rotate before you translate, then what XY values does the software use for translation? Does it take the XY values from the alignment the feature was measured in?

Sorry, this question is a bit hard to convey. See, a while back I had a program that gave me different profile results if I translated before I rotated and I'm trying to understand the theory of why.
  • The process of establishing a datum should always be (1) Level (2) Rotate (3) Translate. That's it!!
    HTH
  • The 'quick' menu alignment ASSUMES that your part isn't even close to being flat or square to the machine, with the FLAT being the big issue.

    IF your part is flat on the machine and the plane you measure is flat to the machine, then there is no real reason to use it's method of multiple alignments.

    IF your part is NOT flat to the machine, or the level (plane) feature is on the side of the part, not on the flat table, then the level & origin is 'required' so that any 2D features are measured & probe comped correctly.

    As for translating (do you mean origin offset?) before rotating, the translate is done to the CURRENTLY aligned part, if all you have done is a level, then the translations will be done to MACHINE axis, and not your rotation axis.

    So, level, then rotate, then origin, then translate (origin offset), always in that order.
  • Level and rotate sets the AXES that you will translate in.

    If you wanted a table and only said it must be 36" above the ground, (in CMM terms) there is a point in the middle of the table that is the centroid, and it needs to be 36" above the ground. So I could put two 40" legs and two 32" legs, and the centroid would be 36" above the ground. Everything on the table would roll right off, because the top would be tilted like crazy.

    Now, if I was forced to LEVEL the table top first, then all the legs would need to be 36" and the top would be parallel.

    You have to set the axis of motion before applying the motion.
  • Hello. I am trying to better understand how alignments work. For example the advantages of doing multiple alignments vs one single alignment, rotating before translating, etc.

    If you don't rotate before you translate, then what XY values does the software use for translation? Does it take the XY values from the alignment the feature was measured in?

    Sorry, this question is a bit hard to convey. See, a while back I had a program that gave me different profile results if I translated before I rotated and I'm trying to understand the theory of why.

    I did have same concern on previous thread

    https://www.pcdmisforum.com/forum/pc-dmis-enterprise-metrology-software/pc-dmis-for-cmms/535862-2-readpoint-start-issue

    Since lots of our programs use 2 readpoints to start, most programs transfer to Datum B ( one of readpoint) first, then rotate from point C to point B, plus some angles offset if needed.

    This is a first alignment for the program, after get the datum A , datum B, Datum C , then program will follow level rotate and transfer ....
  • I have been experimenting a bit...I think I figured it out.

    Level, Translate XY, then Rotate seems to give me the same result as Level, Rotate, Translate XY...........UNLESS I have an offset involved. OR, if I use different features for my X and Y translations.

    Sorry I am having trouble fully grasping some of the responses.
  • in reply to RobOntario
    See my post after you, maybe it will help...However, I think your issue is different. I had the same issue as you recently with a LARGE part that I couldn't square up to the CMM axes. My program kept crashing, unless I did three alignments like this: Measure plane -> Level, Measure line -> Recall A1 & Rotate, measure Origin -> Recall A2 & Translate. If I didn't break up the alignments, it kept crashing. I wish I had a better understanding of alignments. Its just hard to wrap my head around.
  • This is VERY dependent on the features you are using and what you are using them for.

    A cylinder as primary, leveling Z can translate X and Y with no issues of any kind.

    A plane as primary, leveling Z can translate Z with no issues.
    If the secondary is a hole in that plate, it can translate X and Y prior to rotation.
    If the secondary is a plane or line, you can't translate that prior to rotating it, unless you magically happen to have the part sitting in whatever rotation the machine measured in and have it close enough you can't READILY SEE error. Maybe it is off .0010", maybe it is off .0005", maybe it is off .0021". How do you know that is alignment error versus part error?
    Put the part on 45° to the machine axes and try it, you'll have .121" error and KNOW it is the program not the part. Program might not even run if you are off far enough.

    Getting lucky shouldn't be your go to.

    Unless you KNOW otherwise, Level, Rotate, Translate.
  • in reply to Caemgen
    Our programs are a plane primary, then circle or round slot Datum B and circle or round slot for Datum C. Based on what you post, it should be ok.
  • in reply to RobOntario
    I think manual alignment: plane 3 points, line 2 points and 1 point, then move to DC mode, re-measure those feature again...
  • This is VERY dependent on the features you are using and what you are using them for.

    A cylinder as primary, leveling Z can translate X and Y with no issues of any kind.

    A plane as primary, leveling Z can translate Z with no issues.
    If the secondary is a hole in that plate, it can translate X and Y prior to rotation.
    If the secondary is a plane or line, you can't translate that prior to rotating it, unless you magically happen to have the part sitting in whatever rotation the machine measured in and have it close enough you can't READILY SEE error. Maybe it is off .0010", maybe it is off .0005", maybe it is off .0021". How do you know that is alignment error versus part error?
    Put the part on 45° to the machine axes and try it, you'll have .121" error and KNOW it is the program not the part. Program might not even run if you are off far enough.

    Getting lucky shouldn't be your go to.

    Unless you KNOW otherwise, Level, Rotate, Translate.

    I did not try re-measure function. For ( Put the part on 45° to the machine axes and try it,), I will use re-measure to reduce cosine error....
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