XXT RDS CAA - Using Star probes

[[Ri...]]

If any of you with experience or knowledge, I need the Pros and Cons of using star probes on an XXT RDS CAA.
Personally, I don't see the need for them and I see them as limiting the capabilities of the RDS.

[[Ro...]]

Hi Rick,
My 2 cents.. Star probes are fine on the XXT if they're balanced and being used straight down in Z. Once you rotate in any axis other than Z you end up with a cantilevered probing system. Depending on the weight, that can create some accuracy issues. I only use a star probe in the Z axis, and only to measure things like undercuts and hard to access features.

I prefer to use an L probe that's super light if I need to get into a difficult probing area. The overall weight is less and I seem to have less problems calibrating and getting repeatable, accurate results.

[[To...]]

Not sure you can create a star probe using CAA. When it first came out, you were able to create a down stylus and a lateral stylus. However, I can't make that work anymore. Likely, something I'm doing wrong.

[[Ph...]]

We use star probes but they are all balanced (same size styli on opposite vectors) and we only rotate around the -A-. Qualifying a star probe I have to have a second reference sphere position, Inclination 180° and Rotation 0.0° to avoid shanking out.

[[To...]]

Please sign in to view this quote.

CAA qualification?

[[Ja...]]

Pros of star probe:
1) Depending on the length of stylus system, using RDS XXT head (B axis) narrows down your allowable clearance cube from the axis end positions of CMM meaning you need to place part with enough clearance so that travelling to any clearance planes does not hit the limit switches. This will be the case when part is wide and/or length of stylus system is high. In such cases, only a star probe will work.
2) With B axis at 90°, Z axis will hit the limit switch when probe center about 2 inches from the granite surface, so you cannot probe features that are close to granite surface. While a star probe can probe very close to the granite depending on its structure.
3) It is fairly easy for body of XXT head with B axis rotated to hit/touch/scrape against the fixture or the part itself without getting a collision error. While with start probe, stylus shaft gets shanked instead of the XXT head, much better and less expensive fix, except for when the part is longer than stylus length where head also needs to be lowered into the part to measure a feature.

Cons of star probe:
1) Calibration sigma values can be higher than XXT head rotated simple down probes.
2) Rotating to different (A and B) angles provide more flexibility with a single stylus system than having to have individual separate angled stylus systems.

Maybe someone can add more to this.

[[Ph...]]

I use a passive qualification on all star probes using a Vast XXT-TL-3 RDS-CAA Head

[[To...]]

Please sign in to view this quote.

Right, but you're not using the CAA function?

[[Ph...]]

No I am not but Rick only asked about pros and cons using star probes on that head. Not about CAA Function.

[[To...]]

Please sign in to view this quote.

One might assume that when you include the term CAA, that you might be trying to use the CAA function. Otherwise, why include it. However, I will not continue to beat this dead horse 🤣

[[Lo...]]

I use a balanced star probe, all four Styli are exactly the same, for a few high production jobs. Not having to rotate the head saves us several hours a week in run time.