Angles...

[kthompson]

probably a pretty basic question. I'm still very new with no formal training.

Checking 3d angles of plane to plane: What do I have to do to get the angle I want? I mean if it's a line to line, you construct the lines to a certain vector direction, but what about planes? is there a way to construct them to a certain 'direction'? I know I can adjust the true/comp setting to give me what I want, and if you're checking a 70° angle, thats no big deal, but if you're checking a 90° and it's actually 90.1° then you don't 'know' which way it's off, or I don't 'know' how to tell yet. And I don't like having angles that are -90°.

Am I explaining any of this satisfactorily? Anyone know what I'm talking about and can help a po' brother out here?

Thanks

probably cmm 101, but hey, like I said, no formal training yet...


Thanks!

~kev

[dyost]

new also

perhaps you could do an alignment on the angle itself?

[Matthew D. Hoedeman]

You can add a single surface point (or vector point) and dimension it. That will tell you which direction you are off. Simply put, level to one plane, rotate to the other plane, origin to the intersection of the planes (the 'odd' axis does not matter) then look at the vector point dimension.

[cmmguy]

probably a pretty basic question. I'm still very new with no formal training.

Checking 3d angles of plane to plane: What do I have to do to get the angle I want? I mean if it's a line to line, you construct the lines to a certain vector direction, but what about planes? is there a way to construct them to a certain 'direction'? I know I can adjust the true/comp setting to give me what I want, and if you're checking a 70° angle, thats no big deal, but if you're checking a 90° and it's actually 90.1° then you don't 'know' which way it's off, or I don't 'know' how to tell yet. And I don't like having angles that are -90°.

Am I explaining any of this satisfactorily? Anyone know what I'm talking about and can help a po' brother out here?

Thanks

probably cmm 101, but hey, like I said, no formal training yet...


Thanks!

~kev

There is probably an answer to your specific question in a help file somewhere, but you will never remember the answer. It will be one of those things that you will need to figure everytime you do it.

I think that you should experiment on a part with a more obvious answer instead of 90º, maybe 30º instead. This will give you a feel for how it works. Using matt's example of the point also helps in getting this feel for how it works. This is just one of those things that is difficult to grasp until you sort it out on you own. You will always be learning with any CMM software.

Now, with regards to measuring angles in 3D. I know the software allows you to do it, but I am not convinced that you(or anyone) will be able to sort out what it is really telling you with any answer you get in 3D. You would be better educated about the parts (and most drawings depict angles this way) quality by doing your angles in 2D and in a particular view(working plane).

[kthompson]

ok... tried playing with a 70° angle... helped a bit... getting there anyways.... but I switched working planes and used 2D angle, and now on one of the angles I'm checking (and only one, the rest are fine) I'm having the following problem... maybe the problem is just in my head, but still a problem none the less.

(reference attached graphic)
PLN8 lies on the X,Z axiis, PLN10 lies on the X,Y axiis. Switching to XMINUS workplane and doing a 2D angle from PLN8 to PLN10, with graphics on to see what's happening, and you can see the graphics lining up with PLN8, but they are off from PLN10. The measurement result is showing 88.4°, but the actual part, measuring with a protractor is measuring 91-1/2°. This is a sheet metal bend, material following the yellow graphics lines as they appear (no complementary angle stuff).

Why is the measurement not lining up with PLN10??? (and not measuring the same as the part?) Is this a problem, or a problem in my head? Lotsa questions here. Again for clarification, since I can't show the part, this is a sheet-metal bend looking exactly the way the yellow angle graphic lines are showing (except the bend lines up with the planes and the measurement apparently does not).

Thanks again all!

~kev

[Lee Johnson]

Looks like it is going in the wrong direction. The delta values are the same 1.5 degrees try putting in the actual value if you didn't and try changing the order line one line two, line two then line one. does that make sense ?

[dccfreak]

Kevin,

It looks like the angle is being reported as if dimensioned from the inside of the break, and according to the graphic, it is overbent. When you use the protractor, the part probably only allows you to get on the outside of the bend, thus, you are also seeing an overbend there, but, from the outside so the protractor shows the break over 90 degrees where the CMM shows it as being under 90 deg. This would say to me that in order to achieve a perfect 90, the form would need to be relaxed, and at that point, you would see 90 degrees from both instruments.

The correct way to report it would be to change the true/complement setting to correlate with the side of the break the print is calling out. In the case of getting the protractor and the CMM to correlate, you should be able to simply toggle the current setting you have now, although you will end up with a negative value. At that point, it would be a matter of simply hitting F9 on the dimension, and reversing the order in which you picked your planes. This should get rid of the negative value.

Brad

[kthompson]

Actually, it is dimensioned on the inside of the angle, exactly the way it's shown on the graphic. The 88.4° therefor is suggesting the part is overformed... that is correct. However with the protractor, yes checking the outside of the bend, it is showing the bend (and it's verifiable because it's visible to the eye) is underformed. Putting a square on the inside of the form you can see that it is underformed that way also, but pcdmis is reporting it as overformed. And that's weird because you would think it should match with the plane that it's measuring to, but it's not and you can see that by the graphic. And that doesn't make sense to me.

I will try reversing order next time I get a negative angle and see how that works.... thanks on those situations... thanks

[DaveR]

Kevin,

I too am having some problems understanding angles and what PCDMIS is reporting them to be. This may be related to your problems (and then again it may not...).

In an attempt to understand what is going on I constructed a generic line and measured its angle with respect to the x-axis. I also repeated the measurements with a second generic line along the x-axis.

What I found is that repeating exactly the same measurement gave different results depending on the nominal angle for that measurement.

I expected an angle of -5.8 degrees, but the measured angle was either -5.8 or +5.8 depending on the nominal angle. See the screenshot below.

It looks to be a case of changing the sign of the measured angle to minimise its deviation from the nominal, rather than properly reporting the measured angle and leaving the programmer/operator to work out where they have gone wrong.

As I say, this changing of the sign of the angle (plus the possible addition of n*90 degrees) may be related to your problem but even if it is not I'd be grateful to any of the experts out there who could explain to me what is going on and why.

Dave

http://www.physics.gla.ac.uk/~davidr...easurement.JPG

[donnyc]

Measuring Angles

Generally it has been my experience that the workplane and alignment that are active when you insert the dimension are extremely important to an accurate reporting on angles. Plane to Plane it should not be as significant as any 2D features (Line, etc.) I personally prefer to create features from known part data and use the angle between option on the dimension toolbar. This will give you an actual angle between number. This will enable to to determine if the angle is more than 90 deg or less than 90 deg.
donnyc.