Compound angles

[ktanner]

I know in measuring a hole, whos axis is on a compound angle, I have to translate to the theoretical center of the hole in X, Y, and Z, then rotate about the two appropriate axes to the correct angles. My question is, it shouldn't make any difference which angle of the compound angle is rotated first since the rotations are about a fixed point, so why do I get two different positional values depending on which angle is rotated first? Is this a problem with the software, or am I seeing something wrong conceptually? Running 3.7 MR3

Regards,

Keith

[craiger_ny]

You are rotating an axis that is normal to the feature's vector. Can you post your code?

[cmmguy]

A compound angle absolutely makes a difference which is first... It is not like multiplication.
Order of origin translation(before or after) also depends on the drawing...

Do you have a drawing?

[ktanner]

compound angle code

Here is the code both ways

A2 =ALIGNMENT/START,RECALL:abc_dcc, LIST= YES
ALIGNMENT/TRANS_OFFSET,XAXIS,5.1
ALIGNMENT/TRANS_OFFSET,YAXIS,-30.3
ALIGNMENT/TRANS_OFFSET,ZAXIS,-43.8
ALIGNMENT/ROTATE_OFFSET,-26.6,ABOUT,ZMINUS
ALIGNMENT/ROTATE_OFFSET,-44,ABOUT,YPLUS
ALIGNMENT/END

PORT_2 =AUTO/CIRCLE,SHOWALLPARAMS = YES,SHOWHITS = YES
THEO/0,0,0,-1,0,0,27
ACTL/0,0.065,-0.555,-1,0,0,28.231
TARG/0,0,0,-1,0,0
THEO_THICKNESS = 0,RECT,IN,STRAIGHT,LEAST_SQR,ONERROR = NO,$
AUTO MOVE = BOTH,DISTANCE = 10,RMEAS = None,None,None,$
READ POS = NO,FIND HOLE = NO,REMEASURE = NO,$
NUMHITS = 4,INIT = 0,PERM = 0,SPACER = 0,PITCH = 2.177,$
START ANG = 0,END ANG = 360,DEPTH = 8,$
ANGLE VEC = 0,0,1
MEAS/CIRCLE
HIT/BASIC,8,0,13.5,0,0,-1,8.002,0.005,13.589
HIT/BASIC,7.456,13.5,0,0,-1,0,7.453,14.141,-0.014
HIT/BASIC,6.912,0,-13.5,0,0,1,6.9,0.019,-14.696
HIT/BASIC,6.367,-13.5,0,0,1,0,6.369,-14.01,0.018
ENDMEAS/

DIM LOC13= TRUE POSITION OF CIRCLE PORT_2 UNITS=MM ,$
GRAPH=OFF TEXT=OFF MULT=10.00 OUTPUT=BOTH DEV PERPEN CENTERLINE=OFF DISPLAY=DIAMETER
AX NOMINAL +TOL -TOL BONUS MEAS DEV OUTTOL
Y 0.000 0.065 0.065
Z 0.000 -0.555 -0.555
DF 27.000 1.000 1.000 28.231 1.231 0.231 -------->
TP RFS 1.500 0.000 1.117[/COLOR]

Second way

PORT_ALIGN =ALIGNMENT/START,RECALL:abc_dcc, LIST= YES
ALIGNMENT/TRANS_OFFSET,XAXIS,5.1
ALIGNMENT/TRANS_OFFSET,YAXIS,-30.3
ALIGNMENT/TRANS_OFFSET,ZAXIS,-43.8
ALIGNMENT/ROTATE_OFFSET,-44,ABOUT,YPLUS
ALIGNMENT/ROTATE_OFFSET,-26.6,ABOUT,ZMINUS
ALIGNMENT/END[/COLOR][/COLOR]

NO_14_PORT =AUTO/CIRCLE,SHOWALLPARAMS = YES,SHOWHITS = YES
THEO/0,0,0,-1,0,0,27
ACTL/0,0,0,-1,0,0,27
TARG/0,0,0,-1,0,0
THEO_THICKNESS = 0,RECT,IN,STRAIGHT,LEAST_SQR,ONERROR = NO,$
AUTO MOVE = BOTH,DISTANCE = 10,RMEAS = None,None,None,$
READ POS = NO,FIND HOLE = NO,REMEASURE = NO,$
NUMHITS = 4,INIT = 0,PERM = 0,SPACER = 0,PITCH = 2.177,$
START ANG = 0,END ANG = 360,DEPTH = 8,$
ANGLE VEC = 0,1,0
MEAS/CIRCLE
HIT/BASIC,8,13.5,0,0,-1,0,8,13.5,0
HIT/BASIC,7.274,0,-13.5,0,0,1,7.274,0,-13.5
HIT/BASIC,6.549,-13.5,0,0,1,0,6.549,-13.5,0
HIT/BASIC,5.823,0,13.5,0,0,-1,5.823,0,13.5
ENDMEAS/

DIM LOC8= TRUE POSITION OF CIRCLE NO_14_PORT UNITS=MM ,$
GRAPH=OFF TEXT=OFF MULT=10.00 OUTPUT=BOTH DEV PERPEN CENTERLINE=OFF DISPLAY=DIAMETER
AX NOMINAL +TOL -TOL BONUS MEAS DEV OUTTOL
Y 0.000 0.852 0.852
Z 0.000 -0.089 -0.089
DF 27.000 1.000 1.000 28.419 1.419 0.419 -------->
TP RFS 1.500 0.000 1.713 0.213 -------->

[cmmguy]

Translate by the coordinates, then rotate the 63.4º first and then the 44º.
Measure the bore.
Measure the face
Intersect the bore with the face to get a point.
Restore the original alingment
Report the point's location.

[ktanner]

Okay....why?

[cmmguy]

Why, which part

[ktanner]

First, why the 63.4 first?

[Matthew D. Hoedeman]

First, why the 63.4 first?

Yeah, good question.

I know why your set the axis origins first, before any angular rotation (ya gotta have xyz zero at your point of 'view' and all rotations are about xyz zero), but how do you determine WHICH angle first?

[cmmguy]

Because it is the angle that the 44º is "sitting on". If you rotate the 44º first you are not rotating it in the correct view.


I understand why you ask that question. I dont think the 44 is drawn correctly. Who would show an angle that is not inline with the centerline of the feature? It appears that it should be a sectional cut. It just doesnt seem right to dimension a plane that a centerline lays in without it being the angle of the centerline, in fact, I have never seen it done that way.

[ktanner]

So theoretically, judging from the way the print is actually drawn and the fact that once translated I'm rotating about a fixed point in space, I don't see why it makes a difference which is rotated first.

Also, when I check the part using the CAD model, it checks true position of about 0.232, not close to either of the two rotations shown in the code provided. Why such a big error there? The only thing I can think of is that the print and the CAD model disagree with one another.

Thoughts...

[cmmguy]

So theoretically, judging from the way the print is actually drawn and the fact that once translated I'm rotating about a fixed point in space, I don't see why it makes a difference which is rotated first.

The angles dont care when you translate. The drawing dictates that you translate before angle rotation. Dont fixate on the fixed point in space and rotating about that.

Did you try it the way I suggested?


Just curious. In the CAD model, is the 44º angle relative to the centerline of the bore or relative to the view?

[ktanner]

The 44 degree angle is relative to the view.

I haven't tried anything different as of now. I am just trying to understand why. Every way I am visualizing and rotating, ends up with the center of the bore isolated in 2 axes and the face in the other. Like I said I just want to understand why.

[RussL]

My two cents.
Any compound angle can be converted to a rotation and an elevation at that rotation.
Your elevation of 44 degrees is not along section DD.
I calculate your true elevation along DD to be 40.80978 degrees.
I personally would make two alignments to test out what PC D-MIS does.
I would translate to point and rotate 26.6 degrees first.
Second alignment would elevate to 40.80978 degrees.
Unfortuantely, I do not have the time to elaborate.
But if you want to see the math involved,
pick up a book on descriptive geometry.
In other words, if you set the part up on a sine plate,
If the side of the sine plate is parallel to your datum, you would elevate 44 degrees,
But if you set up the side of the sine plate parallel to DD, your elevation changes (to 40.80978 degrees).
Just picture an angled surface on a rotary table and spin the rotary table
Watch your elevation change.
Hope this helps.

[JIM HARRIS]

I deal alot with with these type of call outs.I have had as many as 4 or 5 rotations.The rule of thumb is to always do your first rotation from the primary view then you do your second rotation from your second view.These are not compound angles.they are one angle rotated out of another.A compound angle is very rarely used. If you was to use a sine plate(requires 2 sine plates) for a compound angle there is a fourmala that you have to use to set the bottom plate to.There is a big difference between the 2 kind of angles.