I need to know the difference between the location of a plane to a datum and the 3d distance of a plane to a datum?
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Ok, lets say we are talking about datum A (plane)and in your alignment you have leveled to datum A and the distance from datum A is along the Z axis and you *are* in the Z+ workplane. Still with me? Good. Now. Datum A in this example is actually the table and we are checking a short cylinder about 4 " in diameter, so you now go take 3 hits on top to make a plane. If you go distance 3D distance and select datum A and the plane you just made you are going to get the distance between the centroids of the two planes from the Z+ workplane! What you need to do is change to the X or Y +/ workplane. Anyone of the 4 will work because they allow you to "see" the Z axis. First I would check parallelism, just for curiousity, if it was pretty close, I would immediately delete it. If it is far off, I know something isn't right. Now you could go dimension select the plane and tick the Z axis box. This would give you the Z coordinate of the centroid of the plane you created. If you go distance 2D and select the two planes and tick the Z axis parallel to, it will give the distance between the Z coordiantes of the two planes.
3D distances can be problematic. Proper work plane is very important for distance dimensioning. Sorry this is so wordy, hard to describe cleary and be pithy simutaneously. HTH
Last edited by Wes Cisco; 07282006, 09:16 PM.sigpic"Hated by Many, Loved by Few" _ A.B.  Stone brewery

Does the 3D distance work the same way with circles. Say you have two circles on a flat piece of steel. The circle are not aligned in either axis. Will using the 3D distance give me the distance from the centroid of each circle across both the x and y axis? Similar to using the right triangle formula to find the hypotenuse.Kevin
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Yes, but in 3D, so if your sheet metal is 1" thick and you measure one circle .1 below the surface and the other .9 below the surface and they are 5" apart as the crow would fly in X & Y coordinates, then if you imagine another triangle looking thru the side of the sheet metal so you have a line from .9 below to .1 below. That difference of .8 is the short leg, and the 5" is the long leg, the software should report the hypotenuse of that triangle. Keeping in mind that the 5" dim I have been using in this example is actually the hypotenuse of the triangle created by X and Y coordinates of the circles. HTH If you still don't get it, let me know and I will try to think of a better example.sigpic"Hated by Many, Loved by Few" _ A.B.  Stone brewery
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Originally posted by kmcmmSo what your saying is if I want to get a more accurate measurement I should construct points at the intersection of the circles and the top surface then dimension the 3D distance between the points instead of the circles.
You should get an accurate measurement no matter what, within the uncertainty limits of your machine. The real focus here is not accuracy of measurment, but rather how to tell the software exactly what you want dimensioned. In my example of 1" thick sheet metal and you need to know the distance between the two holes for both the x and y axis. You want to measure each hole and then go distance, 2D and first select either the X or the Y axis and the two holes, (making sure you are in the Z+ or Z workplane), then do the same thing again for the other axis and selecting both holes. If you try to use 3D distance you will get not only the distance betweent he two holes as a crow flies, but also factored in will be any variation in the Z axis height at which each hole was measured.
A print is 2D. In order to extract from the 3D wireframe you create as you program, the 2D print dims, you must be in the correct workplane to "see" the axis and then select the proper axis and the two features.
The work plane example I like is imagine a quarter laying on your table. The Z+ workplane is looking down from the quill towards the table, from that vantage the profile of the coin is a circle. Now bend over and with your eyes just above level with the table; look at the quarter. You are now viewing the Y work plane. You see either a reactangle or a line, depending on how you account for the thickness of the quarter.
The software "sees" two dimensional objects and dimensions in this way. If you are not in the correct work plane, you will not get the correct dimension even if you use the proper icons and select the proper features, the software will see the line, (if in Y) instead of the circle you want. (Z+) HTH
HTHLast edited by Wes Cisco; 07282006, 09:25 PM.sigpic"Hated by Many, Loved by Few" _ A.B.  Stone brewery
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Wes,
Thanks for the help. The reason I asked was I got a PM the other day from another member who asked me a similar question. He wanted to know how to get the distance "as the crow flies" from a part with two holes where neither hole was aligned in any axis. I wanted to make sure I told him corretly. There is alot of knowledge on this forum.
ThanksKevin
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Kevin, there is another perhaps easier way to get what that person needed. After you have measured the two holes, contsruct a line between them. Now make a new alignment, where all you will do is rotate one axis to that line you just created, for this example we will say X axis. So your alignment only rotates X+ about Z+ to the line. Now in Z+ workplane you can do a 2D distance between the two holes parallel to the X axis. This gives you the straight line distance, (as the crow flies), between the two holes w/o being "contaminated" by any variation in Z axis location they measured at. Then recall your previous alignment and move on to the next headache. HTHsigpic"Hated by Many, Loved by Few" _ A.B.  Stone brewery
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Originally posted by Wes CiscoKevin, there is another perhaps easier way to get what that person needed. After you have measured the two holes, contsruct a line between them. Now make a new alignment, where all you will do is rotate one axis to that line you just created, for this example we will say X axis. So your alignment only rotates X+ about Z+ to the line. Now in Z+ workplane you can do a 2D distance between the two holes parallel to the X axis. This gives you the straight line distance, (as the crow flies), between the two holes w/o being "contaminated" by any variation in Z axis location they measured at. Then recall your previous alignment and move on to the next headache. HTH
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