Tool Radius Compensation Start Up Paths

Our Fanuc EDM at work has three options for tool path during compensation start up. I am not long on this machine and it is configured for the third path according to the parameters (and observed operation). My question is, what is the purpose of the options? I am familiar with the middle path where it places the centre of the tool on a line 90 degrees to the start point. I can’t think of how the other two options would be simpler to use, or who or why they would be used.

I agree with you. The middle one should be used, assuming that the start up move does not involve cutting, and the actual cutting starts from the next move. In such a case, the other two options will result in some error at the start point of the cutting.

Thankyou for responding. I would prefer the middle one too but we have not found how to enable parameter write yet in order to change it. I would like to know why the other two even exist? I assume there was a good reason once.

The error on start point definitely is an issue. A job I attempted to do had a feature repeated three times about a center point using an incremental sub program and a rotate feature of the sub program call. I went from a clear position straight onto the profile and around the part, but due to the entry and exit directions the cut at the end of the part was about 2mm different to the start point. If the path was executed under the middle conditions that would not of happened. I verified the maths was correct by checking it two or three times, then removing the tool radius compensation from the program and the start and end points were the same when run through graphics. I guess if your clear of the part and programming all absolute that error on start and end would make no difference. In this case the solution would be to arc in and out which to me makes more unnecessary work calculating an arc that has the end point coming onto the profile tangential to the start point.

Instead of inserting an arc, you may try two linear segments to reach the start point. Maybe, two orthogonal moves.