Help with 1/4 npt G71 on Okuma Lathe
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hyare you braking only threading inserts, or also others ?
when i need to debug threading operations, i stop and inspect thread and tool after each pass, sometimes also recovering the chip from the machine, and having them in order on the table ( color, shape, may tell a few things ); during testing, cutting specs are low, moderated, and after i fix, or at least improve, then i raise them
between others, is important that there are no chips on tool, or inside part, thus operation must run clean; importance of this is higher as threads get lower in size
for such testing, i use a threading code that is performing a tool retract & M0 between passes
possible causes :
... insert interference ( check attached image )
... toolholder interference ( use a marker, and inspect the toolholder as you go, so to identify marks that should not be there, caused by a wrong tool mounting, or chips squished between part and toolholder )
... low quality inserts, that look nice, but simply don't cut ( i take the tool to a clasical lathe, and check it with a veteran )
... improper cooling ( internal coolant is better; if also outside available, try to use 2 nozzles, one hitting insert top, the other hitting insert side, thus using internal coolant toghether with outside coolant may be better than only internal )
... entangled chips ( increase clearance so there to be enough room for the chips to fall, lower doc, etc )
... blind hole ( causing chips to gather/squish at the end; try to attack the hole in 2 or 3 steps, like threading 60% depth, then 90%, then the rest 10% )
... tool overhang ( lower specs as much as possible )
sometimes chips will entangle, one way or another, so i look/listen carefully, and input an M0 not after each pass, but after a few, like after 5, etc, and M0s may be more frequent near the final passes ( for example, tool may behave ok with an entangled chip at the 1st few passes, while an entangled chip right before the last pass, may damage the thread ); for small threads, this requires a bit of silence, because inside a noisy shop is hard to hear a small vibration
refresh operations after threading :
... recut the front chamfer towards the root
... be sure that you use as many spring passes as needed, and listen the tool during spring passes; sound should be clean, cutting chips should not exist, or be minimal
for small threads, the machining tolerance of the bore, before threading, matters, because a bore size that is minimal, will put too much force on the insert, especially at the 1st few passes, so, consider :
... having the bore near the maximum tolerance, and/or
... before threading, thus before the 1st pass, cut a 0 pass ( or more if needed ), designed to deal with any bore variations, so to minimize starting stress during threading operation; in others words, a 0 pass ensures that 1st pass always has constant doc
for small threads, a partial insert may behave better than a full profile insert, simply because there is more clearance for the chip
how you are using an okuma machine, inspect load diagram for each pass, because it can show anomalies that you may not be aware of, or hard to detect; it's sensibility should help, hoping that the little thread can be felt by the machine
by the way, there is an okuma forum here : www.cnczone.com/forums/okuma/
kindly
Originally Posted by Dnguyen91
