Hello i am new to the forum so please excuse me if this thread is in the wrong place.
I work for a C.N.C. company in Manchester and I am trying to develop a simple excel spread sheet to calculate component cycle times. This is for the purpose of accurately quoting potential jobs. I have developed most aspects of the spread sheet and tested them with actual jobs with a successful outcome. I am struggling with the toughest part (turning). We use Fanuc controllers to control Colchester tornado T6M’s turning centres. We use constant surface speed (G96) I am finding it difficult to create a formula to find out the cycle time of a turning cycle (G71).

My first attempt worked well this is what I had:-


Simple turned peg.

Used a turning cycle (G71) and (G70) finishing cycle.

G71U1R1;
G71P10Q20U1W0.1F0.2;
N10G00X30;
G01Z-50F0.2;
X60;
Z-100;
X62;
N20G00Z2;
G70P10Q20;

So my depth of cut is 1mm
Feed rate 0.2
Spindle speed S250

As the feed is feed / rev (G95)
I need to find how many revs per second
60/250 = 0.24spr
0.24 x length of cut (50mm+2mm)
0.24 x 52 = 12.48 secs
Then worked out how many cuts (15)

12.48 x 15 = 187.25sec
187.25/60=3.12mins

This was correct to I applied the same technique to a second job COMPLETELY WRONG.

So I must need another formula but I have no idea what
I bet you all know what is coming and that is has anyone tried to do something similar is so what calcs did you use?
Thank you for the time.