Spherical radii

[Ravenmaniac]

Ok....bear with me as this has probably been addressed before but I could not find anything really definative in past posts to answer this.

Our little QA group is in a deadlock in the approach to the best way to address measuring and dimensioning spherical radii in PCDMIS. The question arose over a part that has a spherical "divot" in it of .320 radial basic with basic dimensions defining the location of the vertex from other datums. Yeah...you know know what's coming up next...the radial swing in the part is defined with a .001 profile callout which now brings us back to using a scanned set of points and looking at this .320 basic spherical radius. We created the point set off of the CAD model and now we're arguing amongst ourselves on what to do with them. The engineer whose prototype part this is wants a .005 profile callout back to datums A,B, and C which locate the vertex and a .001 callout on the form of the swing. (The radial divot is only about .120 deep into the surface as the vertex is above the plane datum by .200.) To help expedite this issue quickly and not drag us into a technique battle I bring this to all of you as I bet his has been an issue to some of you before....Thanx....B

[Schrocknroll]

Is your question how to dimension the aforementioned callouts or are you asking what all should be dimensioned on the radius?

If you have the basic profile information, then the most accurate way to see what you really have is to dimension the profile. The location and size of the radius can be suspect at best when it's a shallow radius.

[Tested]

I don't think you can get anything other than profile. With such a small "divot" i think you will be hard pressed to get anything else that you can trust. Like with diameters the smaller the angle the less accuracy. And it sounds like you don't have much to work with. If you had more tolerance I would feel better about it.

[Ravenmaniac]

Well...the engineer in question is trying to see how the spherical radius deviates from form more then anything. Kinda the way we tend to evaluate polar point radii on small arcs from a known location vs. trying to evaluate the radius as a whole based on measured data. You know the error that can come out of that. I believe he wants a radom scan of the divot and to look at a dimensioned report of polar (spherical) radii per point then as a whole. He's trying to see the capability of his tooling on the CNC vs. having to send this part out for outside EDM work.

[Tested]

The profile back to -A-, -B-, -C- needs position. So I would do a form only. Or construct a point at the theoretical center from -A-, -B-, -C-

[Tested]

The profile back to -A-, -B-, -C- needs position. So I would do a form only. Or construct a point at the theoretical center from -A-, -B-, -C-. set my Datum there and then report profile "formandlocation"

[johnboy]

Profile & TP

'Form only' profile of the sphere, and/or, you could report the 'T' value of each point taken on the sphere.

Then TP (x, y & z) RFS of the sphere to -A-B-C-.

[Sean Harris]

Why not do a best fit alignment of the shpere scan set and profile it?

[Ravenmaniac]

Let's get away from the profile callouts of the problem and try and tell me of how I can report the spherical radii locations of each of those points measured as a spherical radius point (per point, not a set or field of points for mass evaluation with profile)...B

[cmmguy]

I think...

(((X^2)+(Y^2)+(Z^2))^.5)+proberadius
where X,Y, & Z are the uncompensated touches and zero is the basic location of the spherical radius.

[Ravenmaniac]

Yes that was one way we discussed which was using the theorhetical math evaluation of the points, we were just throwing out a few feelers to see if there is a more conventional, easy method of generating spherical radii results. I'm starting to see a desired upgrade option here........B

[Sean Harris]

Ummm isnt this form/size thingy you are asking for also called profile? In your original post you asked for a .005|A|B|C and composit of .001.....unless Im really confused here. To answer the .001 question ( if you have CAD n U said U did) all you need is a BF alignment and profile? The .320 basic dimension is not a question that needs to be answered....... If you need a number for the .320 thats a different thing all together. If thats what you want then zero the SR with a couple "fixed rad" circles ( pretty sure Pc-Dmis wont let you do a fixed rad sphere ) and then measure form and R. size as polar vector points? Which is also profile BTW just a harder way to get there....

[Ravenmaniac]

Yes...I did originally ask on the profile issue and maybe I wasn't quite clear as to my total need. You can evaluate the profile of the 3d point field generated off of the cad but that gives you only the profile of the entire field measured based on the extremes deviating from basic. The engineer involved was looking for 3d polar readouts of the points as well to see specific deviation per point in the field to generate a capability analysis of the tool trying to create it. I've found the profile to be OT and we're probably going to send this part out for EDM but it was a query question on how to look at 3d polar, spherical radii.
Any input is appreciated.........B

[Brian Gudauskas]

Try this, I am not sure it will work for you, but hey.

1. Report the radius of the sphere, make sure max min is on. Turn on text analysis. See if the text values MIGHT have spherical radius in it. I am NOT sure it's been a while.

2. Report the XYZ AND T value of each point in the sphere. If the text analysis doesn't do the radius as suggested in 1., then this will do the trick.

Otherwise the best option is the formula, it's not too difficult.

[JamesMannes]

Good answer Brian. Good to see you back answering questions, were you busy for the last few months? Just haven't seen you around. I will print that one out.