View Full Version : Need Help! Max RPM for threading? HIT-18S, My first thread is off in pitch. Why? Siemens 840C

08-21-2013, 08:38 PM
I'm cutting 1/2-13NC threads and was using 500 RPM. Threads were looking really bad. Torn/Ruff. Went up to 1000 RPM and finish improved but the "nut" would not go on, PD (pitch diameter) was correct with 3 wire measurement, insert was not broken and OD was good. This drove me nuts for over a hour until I found the pitch was off for the first thread. I moved the start point away in plus Z by 1/4" and the problem went away. Seems the machine just needs more time to sync up. Am I going too fast? Does the spindle need some type of speed calibration? No mention of max speed in the manuals I have. This is a 1995 machine with the Siemens 840C control. VER 4. I think I would like to even go faster, what's the limit?

Tony T
08-22-2013, 06:37 AM
What are you cutting with? Threadmill, regular Tap, Roll form Tap ??

08-22-2013, 12:33 PM
Lathe, single point carbide insert. using L97 cycle.

08-26-2013, 09:15 AM
I will be watching this thread since I am soon to cut my first threads with my 18S.
The program guide 2-11 give forumlas for calculating the initial start and end points for threading.
The example at the back of the guide gives a 3mm run in and run out for a 1.5mm pitch thread.
Looks like I might have some trouble threading against a shoulder.
Regards, Ray

08-27-2013, 02:27 PM
I use 0 run in and 0 run out. I set my tool to the side not the center of the point. So up to a shoulder I just program in the Z minus .010 or .020" I have done threads to a shoulder with and without an undercut at the end. If you are using an 1/8" wide insert you can thread up to about .080" of the shoulder. Did not run into problems before now, And I found an old program with 1000 RPM programmed in and that worked. Not sure why I had this problem. Let me know how fast you can go.