GPOST placing F0. Feed Rate on B Rotation in G93 Inverse Time Feed

Question

I recently got Fanuc option G93 for Inverse Time Feed installed on a Toyoda FH500J. I am working toward a goal of having an edit free post for that machine. Right now, I get several lines where an F0. is placed before a B rotation. I end up replacing any F0. with a more appropriate feed rate in the G-Code file. It works, but its not a perfect solution.

The part that will be the first part I cut with this is a 12” cylinder with a helical swept groove. It is a constant pitch. I don’t know why there should be many feed rate changes at all, but the way the post writes it is with a change on almost every line. Then there are the F0. that definitely need to be edited prior to running.

Anyone else out there using G93 on a 4axis horizontal? Any thoughts on what I am seeing?

I am using a cutline milling path and a 1/2” ball end mill. The groove starts at the top and bottom where the cutter basically makes a u-turn as it works its way down (helically) to the center of the groove. The spindle never really has to move in X, as the tool works up and down in Y and Z as the cylinder turns on B.

bmuller · Answer

A problem I had with G93 was really high inverse time feed rates (i.e., extremely short moves) creating numbers too large for the post-processor parameters. For example, the “F0” may have supposed to have been F10000., and the post said nope, only doing 4 digits. You might check your post for its max feed rate.

A feed rate on every line is the nature of the beast in G93. In the example part shown, not using inverse time might be an option. I say that because it doesn’t look like the tool strays from centerline too much. Haas controls have a parameter for part radius that can compensate for distance from centerline, allowing non-G93 feeds.

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