acme threads on cnc lathe

[eject_21]

anyone know what g-code is used for cutting acme threads on cnc lathe with fanuc control? g-76 not working. Thanks

[biff1212]

Why isn't G76 working. I use G76 all the time for acme and stub-acme threads?

[scappini]

G92 quite good, can stipulate each pass. personal preference I use both

[stucaruk]

I use G76 but G 92 will work just as well. If it's not working it's probably because your spindle RPM is set to high, and you can't move the Z axis fast enough to keep up, so it will either alarm out or not work. reduce the RPM to keep the Z axis speed under control and it should work fine.

Stu

[eject_21]

My spindle speed is fine. The minor diameter is good, the pitch is right, pitch diameter is huge (like .04 big). This is my first attempt at acme threads,Im missing something. The machine cuts "normal" threads perfectly.

[scappini]

no difference mate acme or no acme unless your making a mistake with cam software in geometry. are you using Cam software?

no need to feel challenged by this thread.
you will need to take many passes. and perhaps to go sideways to avoid excess load or chatter with your tooling.

can you paste your program to view, and it should stick out like a sore thumb.

Acme threads are 29 deg inclusive. May I ask what diameter and is it a stub acme.

I love to help

[eject_21]

1 3/16"-12 stub. Im not at work so cant paste my program. What do you mean by "go sideways"? Thanks. Im not sure if this will make sense but here goes,lets say i just made a 1"3/16-12 60 degree thread. would i be able to just change the insert,tag the cycle start button and make a correct acme thread? (lets assume the major and minor diameters are correct for the acme thread).

[scappini]

I think so mate.

major and minor diameters are correct.
you have the pitch (12 tpi)
( you have the insert/tool correct geometry )
your speed and feeds are acceptable you say

are you programming in g99 or g98? 95% of the time on lathe you must be in g99 but sure this is the case.

what i mean byt sideways is ok here is an example for the G92 code:

G54G99
T1??M8
G97M3S400
G0X35.Z10.M23
G92 X29.5 Z-120. F2.117
X29.
X28.6
(stay above root)

G0X35.Z9.8
G92 X29.5 Z-120. F2.117
X29.
X28.6
(AND SO ON UNTIL THE ROOT DIAMETER)

Thats all I mean by sideways

Mate, what's the end result of thread and/or alarms your getting, trying to do this. What controller and machine you have?

if you have high spindle speed your exit may look crap.
regards

[eject_21]

The threads look perfect, no alarms no chatter. minor dia is right on, pitch dia is about .04"(1.01mm) over size (mic over wires) The thread gage doesnt even want to start. fanuc control, By changing your starting z from z10. to z9.8 are you making the valleys wider? I know almost nothing about acme threads. Are they supposed to be wider than the insert? If I put it on the comparitor, the insert fits the valley perfectly.

[scappini]

yes they will be wider. I wanted to warn that, as a way around chatter. after my last post

[scappini]

what is your thread gauge? Are you looking for a loose fit.

I am running out of ideas. I'm very logical and practical person. If all else fails, perhaps your testing gauge is non standard.

You 100% certain it's an acme, not square/ trapazoid?

there is no mystical thing to this. There is human judgement error or blip in program in my eyes.

regards

scappini

[scappini]

eject let me show you a typical program I have done a few weeks ago for an acme thread