Hello,
I am having a problem on threading with our Hwacheon CNC turning center. This is the first time I have experienced this. I am attempting to OD thread a 5/8-11 thread on a 3/4 diameter x 3.75 long piece of 303 stainless steel. There is a shoulder turned back .875 from the face of the part. This is what is being threaded. Using a tailstock. The "go" thread gage will thread on all the way til the last 2 threads or so - then it just tightens up - can't go any more. Have tried both top notch and lay down threading inserts - no difference. Using a G76 threading cycle. taking many light passes. there is a thread relief machined up against the shoulder. the only way i can get the thread gage to go on all the way is to program a .002-.003 taper into the threading cycle - kinda opposite of what you would do for a NPT thread. I have threaded thousand of parts on this machine over the last 8 years or so - never had this problem. The last thing i did tonight before calling it quits was to check alignment of the turret - while it is not perfect (.002 when running an indicator in the x axis in a tool pocket), I am of the opinion that this would not cause this problem. As I mentioned, I can get it to work with a programmed taper, but this is obviously not the correct answer. Considering I have to have 500 pcs delivered to a new customer on tuesday, I am in a little bit of a panic. Any input would be GREATLY appreciated.
Thanks,
SR