To extend the length of a thread, there is some information that you have too gather before you write your program, and from my sample, I am going to extend the length of threads on a 3/4" bolt with 10 threads per inch. I want too thread at 300 rpm.
Will assume your lathe does not have spindle orient.Write a program with a tool change with feed rate .1 and 300 rpm. Change display screen to error and run the program. Record what the average following error is in the Z axis. On my lathe it's about .008". Put your bolt in the chuck and change your screen do the diagnostics page. Rotate the chuck until the spindle marker is highlighted on the screen. Use some type of device to mark the chuck and the sheetmetal behind it as a reference point. Go to hand wheel mode and move the center of the threading tool to the bottom of the 5th full thread. We want to teach G54 here at minus .508". Now, 5 threads and the following error in the Z axis. Record the depth that the point of the threading tool is in the bottom of the good thread.
Now write a program #1 with tool change for the threading tool #3 and 300 rpm. Next event call program #2 and loop it ten times.
Now lets write program #2. Pick threading, cycle #1, start point at 1" diameter, Z .2 for two full threads at .1 per revolution. Thread depth = .750 . End in Z @ -4.00. Answer questions for taper and start angle to suit your needs. When this one single pass is complete, the machine will rapid it back to X1 Z.2, now do a position move to X.994 and fill out misc. page on the bottom line G50X1.0 , G50 is an incrimental work shift. Now the tool is at .996 but the machine still thinks it's at 1". When the next threading cycle runs, it will cut 0.003 from each side. This will put the tool at .744". Figure the depth from the bottom of the thread that you recorded from your set up to double check that 10 passes at .006 will put you where you need to be.
Go to RUN menu and select program #1. Hit cycle start and then turn the spindle speed override knob to 0. The threading tool will rapid to the start point but will not go further b/c the chuck is not turning. Very carefully, start to rotate the chuck in the direction that it would normally run and when the encoder marker lines up, it will start to carry the threading tool across the part. Visually verify that the center of the threading tool is in the center of the thread. DO NOT BACK UP OR ROCK THE CHUCK because the carriage will continue to move and you will be out of time. Turn the spindle speed override to 10% and the chuck should start and the tool should make it's first pass following the existing thread and then skimming the bolt till it gets to Z-4. If everything looks good too you, and you are in time, then advance spindle speed to full speed and let it finish the part. Mike the threads or test with a nut to verify the fit. Either add more passes in program #1 or change offset on the wear page.
The main thing is, to be in time when you teach the tool and know what your trailing error is so that you don't split a thread.  |