Need Help!- Thread Lead

[wptcorp]

Ok, I need someone to take me back to kindergarten; I have a Dainichi with a Fanuc 20TA.
We cut tapered threads on it. The thread lead is all over the place. This problem has been coming on for a while but not this bad. I have replaced crossfeed screw, backlash on both axis are good. Lathe is level and headstock is with in .005. I am cutting internal threads, made sure threading bar was not dragging. Put a new Servotech spindle encoder on.

How would one know if there is a problem with a control card, axis encoder, ect.

Dave

[txcncman]

Are you trying to thread with G96? How much lead in are you allowing for acceleration? Is your part turning/moving in your chuck/collet? How much deviation are you getting?

[tc429]

check the timing belt sprocket on the encoder- had one that was loose/wallowed out till the key fell out of it, belt tension kinda drove it, but the feed was obviously unstable...the coupling to the encoder I assume is alright if you just changed it...

All the newer Fanucs run those little 20 pin Honda 'PCR' series POS connectors...weve got hundreds of machines, not a single day goes by anymore when there isnt a scratchy PCR connector causing greif...try cutting a old pencil tip eraser down to a 1/16~3/32 thick 'flap' and cleaning the encoder plug at the control end... Oh how I miss them old blue Honda MR series plugs...they never fail and were so easy to solder...

the amphenol plug at the encoder could have issues too- 99% of the time just unscrew it and sniff it- when they start arcing between pins they get that varnish/burnt motor smell... if it smells burnt, AND its got a blue or brown insert, carefully remove the back half, pick out the snapring, push the shell out- note its usually 'timed' with pin A lined up with the key, and also note its split in the center, and the pins can fall out if fully separated... more carefully split it apart enough to look between the plastic layers for corrosion or arcing...if anything there, you'll need a new plug. IF it has the black insert, its a sealed rubber insert that you cant really clean or do anything with...the plastic ones Ive pulled apart and cleaned many times, getting the pins back in can be fun...

also maybe try programming the slowest speed your spindle will run, and air cut/feed the z at like .1 per rev over as much stroke as you can, watch the 'current' program screen actual feedrate or just diagnostic 801 (or wherever following error is at in a 21) to see if the thing is stable...might shed some light on it. good luck

[wptcorp]

I think i just wore it out! It has been working hard for a few years. Ball screws wear out too. Anyway thaks all for the help.