NC look ahead

VMX42 2011 model with Winmax control.

I posted out some NC code to call up in the middle of a conversational program. The NC merge and industry standard NC options are on the control. It was a trochoidal toolpath and everything worked fine until it gets to a bit where the cutting and repositioning moves are small then it slows down. I'm using a modified Fanuc post from Onecnc without the G54 and G43. There's a look ahead line which is G5.1 Q1. This post works fine on a fanuc control. Am I missing something? Is there a different look ahead setting.

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and everything worked fine until it gets to a bit where the cutting and repositioning moves are small then it slows down

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hy stevie, this should be normal : a cnc is never moving at a speed greater then the program value, thus real feed <= programed feed

a toolpath is a serie of geometrical entities, and the machine will never show an alarm if entities length is too small for the nc to reach the programmed feed; in such a case, motion gets succumbed, but it should keep on going / kindly :)

ps : imagine what would happen if an nc would stop when programmed feed is incorrect : an important fraction of active machines would suddenly breakdown :) however, you should be glad that you have noticed this behaviour, because it is the begining of a new path, that leads to a programing style that creates continous cnc motion; if you would work on an okuma machine, i would start to share you a few tricks; unfortunately, i can't help with tips for hurco, thus i don't know if hurco has methods to deal with this case

Sorted it thanks. It was some settings in the Onecnc cam software that needed changing. In the post processor I had it set to output helical arc moves and the machine control mustn't like that. I also changed it to output arc moves as incremental I and J instead of just a radius and X Y end points. In the trochiodal toolpath when it repositions the Z lifts out of cut slightly and it does this helically. It now outputs a series of small lines and runs at full speed. A lot smoother too. Great.