inside corner radius

[d.evans]

With only 90 degrees of arc, how accurate should I expect a corner radius measurement to be using my CMM?
I've got a part with a R .250" +.000/-.003". I get afew that measure within tol, and a few that don't. I'm taking plenty of hits (13), and spread the hits across as much of the arc as I can without getting into the flat (about 85 degrees). Not sure if I believe my results.
What do you guys think?

[Paul Sarrach]

Why such a tight tolerance? Can I see a pic. Thats tight for a corner Radius.

[bw_bob]

I hate checking a radius with a CMM. The only way to check your work is with a radius gage which is iffy to.How close are your readings together. Have you tried running it several times to see if it repeats. Good luck

[d.evans]

visually check

a callout with that tight of a tolerance?

[d.evans]

I'll try to dig up a pdf.
The mating part has an equally tight, yet opposite tolerance (+.003/-.000). These parts are going to be brazed together, and have to pass a helium leak test. Interference fit, basically.
Originally, this part had a +.000 and minus .001 tol. But they loosened it up for on the latest revision.

[Marty Schwab]

Try editing the start and end points for this feature I like to stay off the flat by about 5 degres. And try increasing the hits to 20. You are probablly at the outer envelope of the machine's capabillity for this but if the part is correct. It should make it in tolerance.

[d.evans]

here is pic

here's the pic. Note, the callout is in the lower right portion of the dwg. AND this is the rev that has the even tighter tol. It is now .003, not .001

[Paul Sarrach]

a callout with that tight of a tolerance?

I'm in stampings. I keep forgetting about the Maching world. Do like Marty stated. You could also play with your xyz, ijk targets.

[Wes Cisco]

I do not feel the CMM can measure a radius with such a small arc to within that tolerance. If I were forced to try, I think I would experiment with the different algorythems and see what kind of a difference they make. I really feel your best method of checking this is by casting on an optical compartor. You might even want to make a custom template with your min and max radii, so you can at least verify that it is in tolerance, even if you can't give a specific number like .2497. HTH

[craiger_ny]

I do not feel the CMM can measure a radius with such a small arc to within that tolerance. If I were forced to try, I think I would experiment with the different algorythems and see what kind of a difference they make. I really feel your best method of checking this is by casting on an optical compartor. You might even want to make a custom template with your min and max radii, so you can at least verify that it is in tolerance, even if you can't give a specific number like .2497. HTH

Right. Measured as a radius I wouldn't even waste my time on it. I will go so far as to say you can't, not with those tolerances. Try vector points, dimension the PR. That might be the best you'll be able to do precisely and repeatably.

Craig

[bw_bob]

Plus you have a depth callout of .100 +/-.005 attached to the radius. I would adjust start /end angle and # of points if you have to check with CMM.

[Perry Fisher]

If I were forced to try, I think I would experiment with the different algorythems

Checking radii was discussed in the basic class I attended. In my notes the instructor recommended using FIXED RAD if the radii location is critical and MIN SEP if the radii size is critical.

[Mike N.]

try this method

At a recent users group meeting this topic was discussed and the following steps were given to achieve both the location and diameter of a small arc/radius

To measure a partial arc/radius:

1. create a "measured" circle
2. edit (F9) the circle and add additional hits and edit the "best fit math type" to "FIXED Radius", edit the NOMINAL DIAMETER, check box to "regenerate hits", when prompted "equal spacing" answer YES
3. ctrl E the feature to execute it and re-capture the measured hit points
4. dimension the "location only" of the fixed radius circle/arc
5. edit dimension tol's to print
6. create an alignment and set origin on fixed radius circle
7. (if using CAD skip this step) F10/Parameters>Probing> enable polar compensation for the active workplane
8. with joystick measure more individual/separate points on arc radius (if using CAD use "vector point" skipping step #7)
9. dimension individual points using the "PR" polar radius function
10. F10/Parameters>Probing> turn off or disable polar compensation

[d.evans]

Checking radii was discussed in the basic class I attended. In my notes the instructor recommended using FIXED RAD if the radii location is critical and MIN SEP if the radii size is critical.

What is FIXED RAD?
What is MIN SEP?

[bw_bob]

At a recent users group meeting this topic was discussed and the following steps were given to achieve both the location and diameter of a small arc/radius

To measure a partial arc/radius:

1. create a "measured" circle
2. edit (F9) the circle and add additional hits and edit the "best fit math type" to "FIXED Radius", edit the NOMINAL DIAMETER, check box to "regenerate hits", when prompted "equal spacing" answer YES
3. ctrl E the feature to execute it and re-capture the measured hit points
4. dimension the "location only" of the fixed radius circle/arc
5. edit dimension tol's to print
6. create an alignment and set origin on fixed radius circle
7. (if using CAD skip this step) F10/Parameters>Probing> enable polar compensation for the active workplane
8. with joystick measure more individual/separate points on arc radius (if using CAD use "vector point" skipping step #7)
9. dimension individual points using the "PR" polar radius function
10. F10/Parameters>Probing> turn off or disable polar compensation

All for a freakin .250 radius..........wow