All -
I had a curious thing happen this weekend and wanted to share it with you.
I'm still trying to figure out speeds and feeds for different materials, and have had to be more conservative at it than I wanted. I'm impatient, and why should I wait two hours if I can only wait one for a program? Anyway, after breaking a few drills and hogging an endmill into a block of aluminum, I have learned to wait. Someone else has already reported the slipping collet business; I now clean and degrease the tool holders and tighten the drawbar better.
Anyway, here's the story. Sorry if it's kind of long.
After much play with aluminum, I grabbed a bronze bar from the scrap box, and proceeded to turn it into little chips (that's ultimately what the machine is for). I noted very quickly that bronze is not aluminum, so I slowed the feed down. When I finished the roughing pass (with an end mill), I switched to a ball-end mill. I got some squealing, so I slowed the feed even more. I still got squealing, so I slowed the RPM, and everything settled down. Until...
I noticed that I heard extra bumping noises. And it got worse. I wanted to wait until I had proof, so I didn't stop the program. In this particular case, I had intentionally used slightly undersized stock, so the program was cutting air for a while (mostly in circles around a vertical rod). The next thing I knew, it cut a groove across the face of my part, almost 1/4 inch off! Proof enough. E-Stop.
It didn't take much to figure out that X and Z were fine, but the Y axis had a distinct problem, primarily in the minus direction. Very evident "bump" noises as the table moved. Another shot from the oiler didn't help (I try to give it a shot every few hours). The noise seemed to get better as I kept moving Y back and forth, but it didn't clear up entirely.
And the machine is only three weeks old. I re-read the manual about trouble shooting, and decided to swap the X and Y controls. Definitely in the Y axis stepper or ballscrew or something.
After a little more hand wringing over what to do, I decided to visually check the Y ball screw. I pulled the way cover screws and pulled the cover back and got a flashlight, only to discover that the screw was coated in incredibly fine bronze powder. Huh, and I thought that's what the cover was made to keep from happening...
I ran the table all the way out and cleaned the screw with compressed air, oiled it, and ran the table back and forth a few times. No more bumping!
Apparently, the rear way cover lives directly under the back edge of the vise, and coolant pours onto it (literally) by the gallon. My tiny steps had created very fine bronze chips that were able to slip between the table and the cover, even though the gap looks too small for even water to pass. I have run a bead of sealant across the top of the way cover frame at the table edge, and don't expect to have any more problems.
The front way cover has a sheet metal umbrella over it, so I didn't seal it. On thinking it over now, I probably will tonight. The gap on the rear side was tiny, too. Even though no coolant really runs to the front, who knows what might get through the front cover gap?
If you develop a Y-axis stepping problem, pull the cover and check the ballscrew. The tolerance is tight enough that very tiny particles will jam it and make the motor stall. Better still, pull the cover and clean the screw now, and seal the cover at the table before you have problems.
Regards,
- Just Gary  |