So I have found something in the matter, and have gone around the problem and have a stable solution in all cases.
So my findings are:
1) when G93 is used and if there is linear move to be done in the same time as rotation there is minimum linear feed that controller uses and this is 0,1 mm/min.
If code requires smaller linear feed it will not controller will not do it and will go with minimum linear feed rate 0,1. This is why in some cases G93 does not produce effect as expected
2) If G94 is sued and there are linear and rotation moves combined in the line of code feed is based on linear feed, so move is executed in the time linear moves would need to do the move with given federate.
If only rotation is present in the line of code than federate value is executed in angular units.
3) to solve this problem I am using G94 instead of G93 but with F specific for each line of code involving rotation of 4-th axis.
To get F value for given feed rate very simple calculations are required.
This strategy is error proof as if F is specified for G94 it can have any value, in particular it can be smaller than a minimum F value controller uses for G93. So for G 94 F can be as small as 0,05 mm/min (this I have tested, but I suppose there is no lower limit for this value).
So in a sense it turns out that G93 is not safe to use and using G94 instead requires exactly the same calculations but is error proof.
Cris.
