I’ve got a job I’ve probably run 100 times, but yesterday started having a z-axis problem. The tool jumps up a bit and finishes the job maybe a 16th inch high.
So I’m thinking either a belt slip or a stepper skip right?..
Regarding belt slip: After I stop the job and recheck z-axis zero. It is still perfectly zeroed. This would rule out belt slip wouldn’t it? If the belt slips, wouldn’t it change the z-axis zero point after it happens?
Regarding stepper skip: As I said, I’ve run this job 100 times with no issue until now. I am using a 0.25" ball I had my plunge set at 32 inch/min machining wood. After the failure yesterday, I was thinking that must have been too aggressive and my luck finally ran out, so I backed the plunge down to 15 inch/min. But the same thing happened. Tool jumped a 16th high and finishes the job too high. Then I check z-axis zero, and it’s still perfect.
Any ideas? If my belt was slipping it would change my zero, right?
Have you checked your Z-motor pulley for tightness? A loose pulley might allow the position to slip in one direction and then move back again later causing your zero to appear to be good.
I did check the pulley. It’s tightened solid, and I replaced the set screws for real screws a while back on recommendation. I can tell it hasn’t moved because it remains on the flat spot on the shaft.
Loose eccentrics? It could be loose enough that the gantry flexes a bit (1/16th of an inch is not a lot), but once the force is gone, in idle situation when you jog to verify zero, the problem might not show?
Oh good, and zero wouldn’t be effected right? Just skips a step during the job and cuts high. But once I shut it down and recheck zero, will it still be the same even though it skipped as step during the job?
Hmm… Oh wait! When I stop the job in Carbide Motion it re-homes automatically after I hit stop. Could that be how I’m not loosing zero but still skipping steps during the job?
Thanks everyone! As an engineer trying to teach myself to be a machinist, this is not the first lesson I’ve learned the hard way, nor will it be my last I’m sure.