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Alignment/Measuring

bigblue97mustang
Hello all,

I'm back with another rapid-fire set of questions:

I'm having a lot of troubles getting my alignments down. So, basically where i work, we make exhaust tubes. I am almost always supplied a cad, with a predetermined origin and rotation orientation for my coordinate system. Because of this, I was told in the PC-Dmis 101 class, I would have to almost exclusively use best-fit alignments. Now, to do my alignment, I typically take four separate hits (using my mouse on my CAD) on each end of the tube in a kind-of plus pattern. Then i start a new alignment, click best fit, select all 8 of my hits, click compute, then ok, ok. So that's my initial alignment. Then I select auto-trigger mode and place 4 hits on either end of the tube (The cut part of the tube, by the way; what will eventually be measured as a plane soon), and create a second best fit alignment using the 8 new auto trigger hits.

After this is done, i shift-left click all my features starting at one plane, then all the cylinders down the part, then the last plane. I construct a pierce point between the first plane and first cylinder, and then the second plane and the last cylinder.

Here's where i get into trouble:

By blueprints typically call out distances between these two points across the X, Y, and Z axis, all separately. X normally goes down the length of the part, Y for the width, and Z for height. My X measurement is 'almost' always in spec, and then my Y and Z measurement is be off, sometimes significantly. This leads me to believe that there is a rotational issue present, likely due to how i built my first alignment. On occasion, my x measurement will be near perfect, then Y and Z be off my 8-10mm. Yet when i check the part to the check fixture the issue isn't present, which only further confirms that i am doing something blatantly wrong. In the PC-Dmis class, we only used the training block, so it was incredibly easy (relatively) to visualize my alignments, and make sure i had all degrees of travel and rotation locked.

Please, someone help me understand what I'm doing wrong, and what i can do to fix this issue. I have been doing this for around 6 months, (did the PC-Dmis 101 course this last December) so I don't know all the lingo or shorthand names for some of these actions i see some people talk about. Please explain how i should be doing it, as step-by-step as you can as though you were instructing an infant, because I'm definitely missing something here.

With my last post after the guy helping me realized I'm an incompetent newb at this, and he broke down what i needed to do step-by-step, it almost completely solved my issue that i was having.

Thank you.
Parents
  • Just curious, when you're constructing the lines to measure the angle between them, what direction are the arrows? As point 2 is the junction where lines 2-3 and 1-2 meet, you want the constructed lines to be consistent. Meaning that if you created a line from 1 to 2, you would want to create the other line from 3 to 2. That will make the direction of the lines coincide.

    I've found that if you were to create one line from 1 to 2, and then a line 2 to 3, the angle measured between them will yield odd results. But if the line vectors are consistent (both toward or both away), you'll get an accurate dimension.
Reply
  • Just curious, when you're constructing the lines to measure the angle between them, what direction are the arrows? As point 2 is the junction where lines 2-3 and 1-2 meet, you want the constructed lines to be consistent. Meaning that if you created a line from 1 to 2, you would want to create the other line from 3 to 2. That will make the direction of the lines coincide.

    I've found that if you were to create one line from 1 to 2, and then a line 2 to 3, the angle measured between them will yield odd results. But if the line vectors are consistent (both toward or both away), you'll get an accurate dimension.
Children
  • in reply to Quality ish
    I'll give that a try. I've noticed that sometimes i really have to play around with the way it get's measured. I'm normally measuring 3d, in relation to eachother, but sometimes I have to switch back to 2d and change the 'relation to' or the 'relation from' selection, then back to 3d. That usually seems to do the trick.

    Also, normally, I don't measure the angle itself, rather report the XYZ coordinates of all 3 points against the nominal values given by my blueprint.

    Though, because of part alignment issues, I have though about switching to measuring the length between 1-2, and 2-3, then measuring the angle created there instead of reporting the coordinates, as this would allow me to create my own alignment which wouldn't depend on using the cad's coordinate system/alignment.

    And as of right now, I still can't get any of the above suggestions to cooperate. It's really burning me up knowing there is obviously some part of this process, that I'm just missing. If someone will tell me how to, I will post some of my programs on here (minus dimension values), and maybe someone will notice what im missing/doing wrong.

    Thank you all for your help thus far!
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