3D Distances ??? WTF!!

[spazus_maximus]

Maybe someone can help here...........This is a very straightforward dimension the distance between two paralell planes. I use two different angles one for each plane A90B0 on the back side & A90B-165 on the front side. I measure 3 points per side then construct bestfit planes>> then use 3d distance for the dimension. This has always worked in the past when compared to micrometer results.
Something happened?!!!<L

Now my distances are off .6mm compared to the micrometer. I thought maybe it was a crash so i repeated the measurement manually using the angles that i use in the program on a 3-2-1 block and got within .00019" Seems that its not a calibration issue....right? So then i added a bare bones alignment.. just leveled one of the planes and made that same plane x origin and tried to dimension location instead of distance. I get the same freakin results...aarg! What in the world is going on here?? this program has been running for 18months 24/6 any help is appreciated

[Paul Sarrach]

is your tip loose?

[Wingman]

Try reversing the order of the two planes in the dimension command and see if you get diff results just for a test. The 2nd feature of a 3d distance is the datum feature. The distance is taken from the centroid of the 2nd feature Normal to the 2nd feature. It might be a case where the two planes are not parallel and the 2nd feature is out and throwing off the results. Or, there may have been a mis hit / bad hit when sampling the 2nd feature? Still 0.6mm is a **** of a lot of deviation.


I know I am a bit anal on this but I get best results when I capture two planes, get a mid plane and level to it, then report 2D distance with MIN / MAX on.

[John Riggins]

Try using 3D distance, point to a plane and see what the results are.

[John Kingston]

is your screw loose?

Cmon Paul, be nice. Actually good point about the tip. Look at all the connections to the Z ram. Recalibrate/qualify the tip. Look closely at the ball too. Possibly some wear or a chip in it that isn't hitting the qualsphere, but is hitting the part, throwing comensation off.

[#2#]

Maybe someone can help here...........This is a very straightforward dimension the distance between two paralell planes. I use two different angles one for each plane A90B0 on the back side & A90B-165 on the front side. I measure 3 points per side then construct bestfit planes>> then use 3d distance for the dimension. This has always worked in the past when compared to micrometer results.
Something happened?!!!<L

Now my distances are off .6mm compared to the micrometer. I thought maybe it was a crash so i repeated the measurement manually using the angles that i use in the program on a 3-2-1 block and got within .00019" Seems that its not a calibration issue....right? So then i added a bare bones alignment.. just leveled one of the planes and made that same plane x origin and tried to dimension location instead of distance. I get the same freakin results...aarg! What in the world is going on here?? this program has been running for 18months 24/6 any help is appreciated

Am I the only one here who questions the use of 3D distance for this?

3D distance will give you the distance between the centroid of one plane and the centroid of the other plane. Lets give an example here.

Plane#1 - Center location 0,0,0 - Vector 1,0,0
Plane#2 - Center location 0,200000,1 - Vector -1,0,0

Now, these planes are parallel and the distance between them that I believe we are interested in is 1.

If you dimension these 3D and get the distance from center to center you get approx. 2000000!

Now, the second part where he zeroed one plane and did a 2d distance - that is a bit worrying. If the planes are not parallel or have poor flatness, a micrometer might give different results than the cmm since its faces are parallel and will hit the high points of the micrometer face locations. A probe might hit the lows and give different results.

[Wingman]

Am I the only one here who questions the use of 3D distance for this?

3D distance will give you the distance between the centroid of one plane and the centroid of the other plane. Lets give an example here.

Plane#1 - Center location 0,0,0 - Vector 1,0,0
Plane#2 - Center location 0,200000,1 - Vector -1,0,0

Now, these planes are parallel and the distance between them that I believe we are interested in is 1.

If you dimension these 3D and get the distance from center to center you get approx. 2000000!

Now, the second part where he zeroed one plane and did a 2d distance - that is a bit worrying. If the planes are not parallel or have poor flatness, a micrometer might give different results than the cmm since its faces are parallel and will hit the high points of the micrometer face locations. A probe might hit the lows and give different results.

Actually, I did question his 3d distance. Also, PC DMIS uses the 2nd feature as the Datum and reports the distance to the centroid of the 1st feature as measured Normal to the 2nd feature. At least PC DMIS 'says' it does it this way.

[#2#]

Actually, I did question his 3d distance. Also, PC DMIS uses the 2nd feature as the Datum and reports the distance to the centroid of the 1st feature as measured Normal to the 2nd feature. At least PC DMIS 'says' it does it this way.

Sorry, missed your post. I'm not so sure about it using the 2nd feature and measuring normal for 3D. I know that is what it is supposed to do for 2D. To be honest, I always report perp. or parallel to an axis and do an alignment before that if it is needed.

[Wingman]

Sorry, missed your post. I'm not so sure about it using the 2nd feature and measuring normal for 3D. I know that is what it is supposed to do for 2D. To be honest, I always report perp. or parallel to an axis and do an alignment before that if it is needed.

I do the same thing. But then, I think we are anal!!

[Paul Sarrach]

I never use 3D Distance to a plane. I always make one plane then a take points on the other and will report them under a Report Comment. I have been questioned on it and they always accepted my reason for reporting it that way.

[Cumofo]

I do the same thing. But then, I think we are anal!!

http://www.uniquemedicaltoys.com/IMA...on_259_440.jpg

http://mud.mm-a2.yimg.com/image/2447328147Ohh realllly!




G

[spazus_maximus]

It appears to be a paralellism issue (one high point on the back side). I think im gonna go with wingmans suggestion using the mid plane to level & soforth. ~~With a 2d distance i can always tell whats going on.

[Matthew D. Hoedeman]

I never use 3D Distance to a plane. I always make one plane then a take points on the other and will report them under a Report Comment. I have been questioned on it and they always accepted my reason for reporting it that way.

That's the way I would do it as well. That SHOULD give you the same readings AS IF YOU WERE using micrometers at the point. HOWEVER, there is also the possibility that the planes are NOT exactly flat, either. What about measuring a plane (and a couple corners as well) and doing a FULL alignment, then measure points at the SAME YZ on each side and report the distance between them in the X axis? THAT sould really give you the same results as micrometers.

[spazus_maximus]

Thanks Matt I think thats dead on where i need to go.


I love mullets!

[Paul Sarrach]

That's the way I would do it as well. That SHOULD give you the same readings AS IF YOU WERE using micrometers at the point. HOWEVER, there is also the possibility that the planes are NOT exactly flat, either. What about measuring a plane (and a couple corners as well) and doing a FULL alignment, then measure points at the SAME YZ on each side and report the distance between them in the X axis? THAT sould really give you the same results as micrometers.

I love it when the All Knowing One agree with me..
http://i178.photobucket.com/albums/w...h326/zeus1.jpg