Min Retraction Fail

[tomGKJVK]

I've already moved on and just put full retraction back on, but I'd like help understanding why this didn't work so that I can avoid it happening again.

When using mid retraction for my surfacing op, the program surfaced the upper angle, then the chamfer for the hole, then it did not pick up high enough and gouged the part when coming across to start surfacing the corner radius.

In simulation, it did not gouge the part, it looks like it barely clears.  but the part did get gouged.  All features came out great.  Offsets were good.

Attached is a simplified cut from the model, can't share the whole model.  The problem op is the one labeled Min Retract Gouged Part.  This is the second to last op on a lengthy part.  Also attached is pic of gouged setup part.  

What did I do that caused the software not to clear the part on this step?

[seth.madore]

Thank you for bringing your question to the forums!

What machine are you on, and what post processor are you using, if I may ask?

[tomGKJVK]

This is on a Haas VF2 with the Haas pre-NGC post.  The only thing I modify on the post is to assign the Air option to M54/M64.  Last time I updated was 9/27/18.

[seth.madore · Accepted solution]

If you don't have "High Feedrate Mapping" set to "Always Use High Feed" you likely encountered what is called a "Dog Leg Rapid" gouge. Haas (after all these years) cannot control the position and timing of 2 axis during a rapid movement. Think of it like the shape of a hockey stick. One axis is going to arrive at it's destination first. This motion can cause a gouge in the case of "min retraction"

The ONE! thing I do like about Fanuc is that there is a parameter to change this behavior.

[tomGKJVK]

Wow, that does make sense but how unfortunate.  Seems so simple.  Thus, that's the value of using high feed rate for rapiding instead of true rapid.

So, if I want to be able to slow down the rapid during operation, I'm best to just stick with Full Retraction so it's always clear of the part?

[seth.madore]

That would be my advice, yes.

-EDIT-

And, you may find that your machine likes 100% rapid moves a lot better than high feed moves. High Feed moves take on a whole new line of accel/decel parameters and it may shake the fillings out of your head if you have a lot of moves