G93 Inverse Time Mode

I'm trying to write a Python script to add G93 to a XZA machine. I'm not having a lot of luck figuring it out. I assume I need to use trig to calculate the distance moved and I think I have that correct but I keep getting following errors from what I assume is too fast of a F word. Anyone have any ideas on the proper way to calculate the F word for inverse time mode?

Thanks
JT

That doesn't make sense, the feed rate should just be throttled if an axis can't keep up (unless this is a complex kins)

I have never used G93, so I am not really qualified to comment, but that has never stopped me in the past.

As I understand it you need to calculate how long the segment should take, in minutes, based on path-length / speed.
Then the F-word is the inverse of that time.

Actually, you can miss a step, the F-word just needs to be (speed units/min) / (length in machine units).

I note that the docs state than an F-word is needed on every motion line.

It's just a simple Axis sim with the A axis added and Y removed. It seems like only the really short segments are the problem.

JT

I am not qualified either :laugh:

The person who wrote this seems to be
www.eng-tips.com/viewthread.cfm?qid=200454

F(code) = 1(minute) / (time = 3D distance/velocity)
The 3D distance of the move is calculated in model coordinate space at the NC control point, not in machine coordinate space and not necessarily at the tool tip. For example, a 5-inch move at 50 IPM takes 5 50ths of a minute, yielding an inverse time calculation of 1/.1 and an F-code of F10. The same 5-inch move at 700 IPM would be 1(minute) / (time = 5 / 700) or (1/(5/700)) or (1/.0071428) or F1400.168

That sort of makes sense to my long disused maths head

regards

PS Looks like you got plenty of answers on the users list
Once they get over the 'F Word' thing, you will probably get the same answer

ArcEye wrote: F(code) = 1(minute) / (time = 3D distance/velocity)

Yes, but 1 / (x / y) is the same as y / x

So, there is no point doing 1 / ( distance / speed ), you can just calculate ( speed / distance ).