Accurately measure small radius size and location - not runout

[Krisj]

I've been running into quite a few radius runout checks recently and I was curious if anyone has come up with a decent way to measure them. I can't show any blueprints but I used my paint skills to mimic 2 examples of recent ones. Example 1 is just a .740-.750 width to the radius runout of both sides of a tab, and example 2 is profile to radius runout of a cutout.

The way I was thinking of doing it would be measure the radius using as fixed_rad circle, measuring the size of radius (via http://support.hexagonmetrology.us/l...-of-small-arcs), and offsetting the measured radius value from the location of the fixed_rad circle. I'm not sure how accurate it would be and I haven't been able to test and correlate it with say holding a pin to the radius and measuring off that. My only concern would be that the fixed_rad best fits based on the inputed radius value, so if I use nominal radius and it measures differently maybe I should re run the circle with the measured value?

Hoping someone has some input or another method, thanks all!

[Caemgen]

distance, add (or subtract) radius

It does the math for you, you don't need to code the variables.

If the feature it is coming from is also a circle, make a point of it, or it will add/subtract that radius as well.

[Krisj]

distance, add (or subtract) radius

It does the math for you, you don't need to code the variables.

If the feature it is coming from is also a circle, make a point of it, or it will add/subtract that radius as well.

Cool! Didn't know that was a thing. What about measuring the location of the radius itself? Fixed_rad with nominal, get size, measure again? Or just measure once? Fixed_rad position always worries me

[Caemgen]

I tend to use fixed radius when I can't get the machine to figure it out on its own repeatedly (within .002").

I use the fixed radius X, Y, Z (as applicable) for location.

I then make an alignement to that location (x, y and z) and do an output of the circle for Polar Radius.

After the output is generated (say on cir11) I add .hit[3] to the cir11.

This will give that one point's polar distance from the XYZ center, and I report that as the radius. This requires there to be a hit number 3 of course.

This is of course NOT what I do if the radius is +/- .001" or something. This is for the standard open tolerance radii.

[Krisj]

I'll have to try this, thanks!

[william]

The CMM really isnt the right tool for the job. It’s sort of like pulling out your calipers and trying to check it that way. An optical comparator or vision system is better for this.

[RandomJerk]

That print is no good for that callout.

You aren't checking runout, which IIRC is not legal for a radius, you're checking profile. However, you're also indicating limit tolerances inside of the basic boxes.

If you have CAD, you need to do a series of open linear scans between whatever the start/stop points of the surface(s) indicated by the profile callout, combine those scans into a single scan, then report profile for form AND position (as indicated by the |A|B|C| FCF).

If you don't have CAD, you can still do it, but you'll need to calculate the correct XYZ and IJK for the individual hits, or program auto features to the correct nominals. Combine all of the features into a single scan and report profile per above.

[Krisj]

The CMM really isnt the right tool for the job. It’s sort of like pulling out your calipers and trying to check it that way. An optical comparator or vision system is better for this.

Agreed, I try to use comparator when able and even hold pins/radius gages when possible. But in the case of the tabs there are 50+ of them. Would take too long to check them all on comparator.

That print is no good for that callout. You aren't checking runout, which IIRC is not legal for a radius, you're checking profile. However, you're also indicating limit tolerances inside of the basic boxes.

My drawing doesn't show all the views but the profile is all around the cutout and the only nominals that are given are to the radius runout and the radius is toleranced. I feel like the radius should be a nominal to do profile off of but not sure. Might put it in to have the print looked at.

(basic box around limit in example 1 was my mistake, fixed and reuploaded to avoid confusion)

[RandomJerk]

Agreed, I try to use comparator when able and even hold pins/radius gages when possible. But in the case of the tabs there are 50+ of them. Would take too long to check them all on comparator.




My drawing doesn't show all the views but the profile is all around the cutout and the only nominals that are given are to the radius runout and the radius is toleranced. I feel like the radius should be a nominal to do profile off of but not sure. Might put it in to have the print looked at.

(basic box around limit in example 1 was my mistake, fixed and reuploaded to avoid confusion)

If the radius is part of the zone that includes profile, it should indeed be basic. I'm thinking someone somewhere thought they were being "smarter than the standard" by giving a larger tolerance to the radius knowing it's difficult to measure accurately as a radius without understanding what a basic dimension is in re a profile specification.

[louisd]

Neither of these examples are controlling runout, by definition.
Runout is form deviation relative to a circle or cylinder (circular or cylindrical) as measured by Total Indicator Readout TIR.

What you have in both examples are distances between intersect points, which include radii.
Example 1 is the intersect point of the Bore and boss to make the left edge of the .740-.750", mirrored on the right side.
Example 2 is the intersect point of the .020r and the outer diameter, mirrored on a common datum rotation from datum center.

I would make a routine to measure both examples as defined: measure individual radii, then create tangent intersect points for each intersection.

[Krisj]

I think "radius runout" is a term used within my company not per GD&T. Pretty sure they use it to control clearance mostly, though I wish they would pick an easier way to control it (like the tangency of the radius? or something else)

[Josh Carpenter]

Louis D is correct, and I changed the thread title to reflect this.

KrisJ, see if you can gently guide your coworkers to not use incorrect terminology. Tell them they don't want to risk sounding like fools.

FYI... the best way to draw a blueprint to control small radii is actually right in one of your sketches: simply use Profile.