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Use Negative ‘A’ Angles to Get Closer to the CMM Table and Have More Clearance

Cris_C
Here is a simple tip that has probably already occurred to many of you, but it seemed worth sharing especially for those who are accustomed to Renishaw probe heads. The Hexagon HH-A probe heads are offset from the pivot point on the A-axis and can move in both positive A angles and negative A angles. So, many probe orientations can be reached with two different angles.

I prefer to use only negative A angles for my measuring routines for the following reasons:
  1. You can get the probe closer to the table. On our CMMs, with just 4" tall fixture plate standoffs I can raise the part enough to measure under it. The image below shows the lowest distance that can be reached on our Hexagon Bridge CMMs with the probe at two different angles that have the same probe vector.
  2. The probe does not swing around as much. For example, going from A90B90 to A-95B-90 will only change the probe orientation 5 degrees, but it will require a wild swing of the probe - what our CMM operators have named "Crazy Moves". It looks cool but it is not efficient and requires a lot of clearance.
  3. There is more clearance beneath the probe - Less likely to hit a fixture or something on the table.
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  • Agree! Now, if there were an easy way to convert the programs that uses the "ballsack" angles to the more "eunuch" style...
  • Agree! Now, if there were an easy way to convert the programs that uses the "ballsack" angles to the more "eunuch" style...

    Making a macro that automatically converts the angles is on my todo list. I mirror a lot of programs for a left/right version of many parts. The first step after mirroring is adjusting any angles that have a "ballsack" angle. I'm glad it isn't just my mind that gets that visual.

    Really, I wish that when the probe head was created it was such that all the angles larger than 90deg were on the positive side rather than the negative side. I would say there is no need for the probe to go in both directions, but it is really handy when using cranked styli. So I guess there is an exception where I may use positive angles.
  • Agree! Now, if there were an easy way to convert the programs that uses the "ballsack" angles to the more "eunuch" style...

    Sack clearance has always been an issue of mine.


  • Making a macro that automatically converts the angles is on my todo list. I mirror a lot of programs for a left/right version of many parts. The first step after mirroring is adjusting any angles that have a "ballsack" angle. I'm glad it isn't just my mind that gets that visual.

    Really, I wish that when the probe head was created it was such that all the angles larger than 90deg were on the positive side rather than the negative side. I would say there is no need for the probe to go in both directions, but it is really handy when using cranked styli. So I guess there is an exception where I may use positive angles.

    Definitely not just you making that comparison . . .
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