ballen
Diamond
- Joined
- Sep 25, 2011
- Location
- Garbsen, Germany
I was doing a nearly final pass on a steel part, about 30mm (1 1/4") diameter and 300mm (12") long on a cylindrical grinder. This was between two dead centers with moly grease, 80 grit white AO wheel, taking off a couple of microns (about 0.0001"). Plenty of coolant, no sparks visible, steady low hum from the hydraulics and the hiss of the wheel. Then all of a sudden, 2/3 of the way down the part, starts periodic pulses of sparks, timed with the revolutions. I can hear it too. I hit the rapid retract, put an indicator on the part, and sure enough, it's not running true any more, 6 or 8 microns (about 0.0003") of runout, that was NOT there before. So I pulled off the part, cleaned the centers and the center drillings, fresh grease and it ran true again. Fortunately the important thing for this part was straight, round, parallel but NOT the diameter, so I was able to grind it down further.
But obviously something happened to one of the center drilling or dead center that threw it out of round. Can someone tell me what? Did some grit or swarf get in there? Or did it gaul internally? Or ??? And how can I avoid this in the future? In this case the center drillings were bigger than usual, is that part of the problem or the cause?
Here is a chart of typical center drill sizes for lathe work (click image to enlarge):
Is this also the right thing for cylindrical grinder, where the load is less? Or is smaller better to avoid problems like the one I describe above? I'm slowly learning how to use a cylindrical grinder, and am pretty sure that the experienced old hands here can tell me exactly what I did wrong and how to keep this from happening again.
But obviously something happened to one of the center drilling or dead center that threw it out of round. Can someone tell me what? Did some grit or swarf get in there? Or did it gaul internally? Or ??? And how can I avoid this in the future? In this case the center drillings were bigger than usual, is that part of the problem or the cause?
Here is a chart of typical center drill sizes for lathe work (click image to enlarge):
Is this also the right thing for cylindrical grinder, where the load is less? Or is smaller better to avoid problems like the one I describe above? I'm slowly learning how to use a cylindrical grinder, and am pretty sure that the experienced old hands here can tell me exactly what I did wrong and how to keep this from happening again.