Question about alignments

[kll985]

Hey Folks,

I've been lurking at this sight for about 3 or 4 months. I appreciate all the input you have.
Now it's time to ask a question.
Probably simple but I am stuck with it.

I am using version 4.1 on a Starrett machine. After I do my Manual setup on a fixture I go into Dcc mode for a Dcc setup.
After I measure my features and set up another alignment the software flips my rotation direction. It is a Plane, Line, Sphere setup. The Origin and the Level are correct, just the Rotation is moved to a different direction.
Do you have any thoughts on this?
I suspect I'm just missing something easy.

Thanks,
Ken

[Matthew D. Hoedeman]

Are you constructing the line in the correct direction? It is very specific, ya know. If it is 2 vector points and you construct a line, the order will determine the 'direction' of the line and thus the + or - for the rotation when you align.

[T Miller]

Are you constructing your line or maybe taking the hits in reverse order?

[craiger_ny]

What are you rotating to the line I assume? The rotation folows the feature's vector (in this case think of it as which way the line points). If it is constructed you could pick your features in reverse order to change the vector, if it is measured you could measure it in the other direction. Or you could just chose to rotate the opposite (X minus if you are rotating X plus for example) axis direction to the feature as is.

Craig

[kll985]

Thanks for the quick responses
I am taking the hits for the line in the correct order.
The rotation is flipped -90 deg. which is what is confusing me.
180deg I would understand.

[T Miller]

The only time that happens to me is when my level is in the reverse order. -z and not +z
I use 3 diameters for level in the x plane most times

[craiger_ny]

What workplane are you in? Are you using a 1-2-3 alignment or are you doing it by picking the features and doing each step yourself. You might want to look at the dialog and see what it says about what axis is being leveled, rotated etc. PCDMIS defaults to a scenario that is dependant on what workplane you are in. You can overide that scenario with the drop downs.

Craig

[William Johnson]

What axis are you rotating about, and what work plane are you in?

[kll985]

I took a plane in the Y-
Then took a line in the z-

Here is the code for the 2nd alignment
=ALIGNMENT/START,RECALL:A1,LIST=YES
ALIGNMENT/LEVEL,YMINUS,PLN2
ALIGNMENT/ROTATE,ZMINUS,TO,LIN3,ABOUT,YMINUS
ALIGNMENT/TRANS,XAXIS,SPH1
ALIGNMENT/TRANS_OFFSET,XAXIS,-4049.88
ALIGNMENT/TRANS,YAXIS,SPH1
ALIGNMENT/TRANS_OFFSET,YAXIS,-987.31
ALIGNMENT/TRANS,ZAXIS,SPH1
ALIGNMENT/TRANS_OFFSET,ZAXIS,-1249.79
ALIGNMENT/END

[Paul Sarrach]

Am I correct to say you are taking this manual alignment on a base? Does it not have 3 spheres?

[craiger_ny]

And you are saying that when you rotate ZMINUS to LIN3 that actually XMINUS rotates to it?

[Don Ruggieri]

Consider this -

Most people lay their part on the table relatively square to the CMM axes. X+ to the right, Z+ is up, Y+ is back, or something similar. Certain assumptions are made, key among them is that the part's XY plane is very close to the machine's XY plane. This is important because lines (and circles) are 2D features. They need a reference plane in which to line. By default, this is the XY plane with any new program.

In your example I see that you are levelling not to the XY plane but instead to the ZX plane. Consequently, the default plane is not good for you. You need to establish the reference plane before measuring the line. To do this, you want to measure the plane and then level to it, as Y- in your case. After that, now measure the line and the remaining alignment features and then complete the alignment.

It is IMPORTANT to do this from the start, for the manual alignment. The level MUST BE ESTABLISHED before the line is measured, if the line is not in the XY plane.

Try it out and let us know if it puts you on the right track.

[kll985]

Ok I tried the setup again following Don's advice. It wants to do the same thing. (Rotate around the Xminus)
There are 3 tooling balls but we usually use the fixture base as we have been having a terrible time getting Iterative and Best fit alignments to work correctly.

Did I mention we are new to PCdmis as of September this year.

[bw_bob]

Could you provide a pic. Might make it a little easier.

[kll985]

Did I figure something out?
I tried the set up using a longer line in the Xminus direction and Don's advice.
This time it came out correctly.
Is there a minimum length for a rotation line?
Could the CAD be messing with it.
The original line was about 12"
The new one is about 30"
I know I should've used that one first, but I didn't think it would matter.

Thanks again,
Ken