Machine malfunction-- now that was fun

SDE

Well-known Member
I put a good part in the indexer, that is mounted to the table of a CNC drill, and pressed the green button. About two minutes later, I hear a BANG. This was the second part and the first one had run just fine. The pulley tap, which costs about $35, had snapped into two pieces. For some unknown reason, the indexer had rotated counterclockwise and had re-drilled the first hole, instead of drilling the third hole. The tap had tried to put threads into the third location, where there wasn't a hole.
Yesterday, I again had to run a part that required three radial holes, spaced at 120 degrees. Instead of being able to trust it, I needed to watch it, to see which direction it would rotate. Every part I ran(4 so far), it would randomly rotate counter clockwise. When it did, I would stop it, and manually rotate it to the correct location and have it either drill or tap in the correct location.
Isn't it odd that I can run it, but the supervisors have decide that no one else will be able to run it until it is fixed? I have Monday off and someone will look at it then. It appears to need new bearings, but I do not know if that makes it rotate the wrong direction.
 

There should be a pawl in there that locks it in position. Maybe not economical to repair.
 
Are you running a program, or running it manually? There may be a stray g code in the program that can be edited out.
 
My first guess would be a bad connection in the wiring to the indexer. Either a loose connection at a harness connector, a broken connection from flexing, or coolant has gotten in and shorting it out.
 
That reminded me of a page collator I ran once. It would randomly 'forget' to turn the receiving tray. I eventually found that it was overheating some component and worked much better if a fan was blowing on the housing under the tray.
 
Reminds me of an ancient Rockwell NC turret mill at a place I worked at years ago. They used it mainly for machining face bars for forklift masts. While milling the notches along the top it would sometimes go back an run the mill back through one it had already done. Sometimes it would go back and drill the same hole. Totally random.
Once when I was running notches it decided to cut one slot diagonally and then proceeded to finish the rest as programmed.
 
The indexer has a program in its control. It indexes with a G85 code in the part program.
 
As Pappa Noel said, is it a Haas? More specifically, a brand new one less than 1 year old with the Next Generation Control?
 

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