Distance between Planes?

[Guru Gill]

How do you measure distance between to not perfectly verticle planes. Should I measure at two points ie. the distance at the top and one at the bottom. But the dimension given on drawing is single.

Thanks
G S Gill

[Tested]

You need to determine from the print where they want this distance. If the planes are drawn non-parellel to one another the drawing should reflect this.

[rangerboat72]

You need to determine from the print where they want this distance. If the planes are drawn non-parellel to one another the drawing should reflect this.

Exactly...

If the drawing does not specify an angle, it is to be assumed parallel or perpendicular...

[kbotta]

(Implied)

[Ravenmaniac]

Distance..........

Be aware of some things here.....

1st....When you measure your planes, if those planes have taper in them from top to bottom or a form issue with say, flatness, that will be a part of your of distance "equation" when PCDMIS does it's analysis. The software will try and establish an "average" location of the plane based on your levels and primary alignments.

2nd....Analyze your pattern of measurement (how you displace your points about the planar surface) this also affects how PCDMIS measures distance. For example, let's say, that if your planes have a .002-.003 dwell in the center of them and you take points all over the planar surfaces, the software will try to establish an "average" planar reading based upon the center of the centroid that you create with your point pattern. That is to say using the same example, that if you took more points towards the edges on one reading and them took them again in a pattern more towards the center, you'l find the two planes you just measured won't be in the same location and the distance readings will be affected.

What you've ventured into is a classic example of how cmm's when measuring certain criteria are not absolute. You can take 100 points on each of your two planes and find a distance generated and then find that a deltronic pin .002 under that reading won't pass completely between them without binding. It's here you have to use a little common sense and like some of the other guys have said, see if there is a form callout on the print and if not, question why if that distance is critical for the part's function.

Hope this helps....B

[cmmguy]

Why are they not parallel? Are these "Planes" the sides of a part that have draft on them? Is that why they are not parallel? Is it by design.

[Guru Gill]

Yes , According to Design Engineer they have draft on them. But it is nowhere mentioned on the drawing. I think the Drawing need to be updated.
CMM is a new thing in our company, so I think they have to be more careful before issueing a drawing.

Thanks
Guru Gill

[cmmguy]

Then you need to measure the theoretical corners at the top(assuming that it probably also has a radiused corner).

You could measure planes on the sides and the top and intersect each to create lines and then work it out that way. Or you could measure a line on each side and the top(sort of in a cross-section format) and intersect those to come up with points and then do the disstance between them.

[tking]

If that's the case then the drawing should specify dim + draft or - draft, + draft would mean you measure the smallest and expect the distance to get larger going away from that level, - draft would tell you to measure the largest distance and expect the dim to get smaller going away from that level.

Whew! Breathe, blonde moment.

TK

[Ravenmaniac]

Ohhhhh.....!

After reading further I see your problem isn't one of the software's abiltiy analyzing distance but one of an engineer giving you a print that's got you running in circles. If you're looking at a print that has drafted walls and a distance callout is on it between the alledged planes it better have 1.) the draft angle and 2.) the distance either referenced at the top or bottom of he draft. Usually, most engineers here will use the witness lines from the callout to point out either the tangent points at the top or bottom of the walls in question. Sorry about the misread! -B-

[Paul Sarrach]

If you are going to get the print change, maybe you can get them to make that a Surface Profile call out.