I finally finished up the servo driven bt30 project, mostly anyway. The new head assembly is built but i wanted to do some testing before rebuilding the z axis with new head. I bolted the new head down to my machime table horizontally and bolted some aluminum stock to the existing head for doing some test cuts. I had to do some dynamic balancing on the big 80t servo pulley, but the spindle runs smooth as glass at 12k, no balancing needed there. I proceeded to do some test cuts to see if the 1kw servo was performing as expected. It seems to top out at about 1hp at its peak torque rpm before it gets a lost phase error. Should be capable of much more than that for at least short durations, but thats a separate issue that i will talk with dmm about to hopefully solve.
Theres 2 other issues that im trying to figure out, most lilely related to eachother. After testing peak power i did a couple finish cuts to see what kind of surfave finish im getting. It was not so great. Not terrible but definitely a chattery look to it. Finish cuts were done with an 8mm 3 flute that i use pretty often. In my current 2.2kw chinese spindle, this endmill gives a beautiful finish and usually has 3 or 4 tenths runout on the flutes. In the new bt30 spindle, run out was even less for these test cuts, about 2 tenths. Also keep in mind that vibration levels are very good, at least what i would consider good. With my hand on the nose of the spindle, i dont think i could feel the difference between running and not running if i had ear plugs in. So why the bad finish if there's no vibration or runout when the same tool gave perfect finish in the 2.2kw spindle? The other issue that i believe is related is an odd occasional noise. To me it sounds like a bearing race letting go now and then but i can be sure. its an intermittent noise that happens for a couple seconds at a time with breaks between and seems to mostly go away after warming up . I Mentioned in my other thread that the top bearing of the spindle had a not so tight fit of the outer race. It would slowly spin in the housing when turning the spindle by hand. I addressed this issue with a wave spring and ring above it to apply pressure to the spring. The spring pushes down on the outer race of that top bearing with about 25 pounds so i doubt that race is slipping. When assembling i put a mark on the outer race and the housing so if i pull it back apart, i will know if it slipped but i very much doubt it. My concern is the 2 preloaded bearings in the nose. Maybe the nut was not torqued properly? Im not sure how i would check this without completely tearing down the whole spindle. The top bearings need to be pulled to expose the nut, but theres no way to pull them. As far as i know, the spindle shaft needs to be pushed out first, i guess with the preloaded nose bearings coming along with it? There is a bolted on nose cap that clamps the outer races of the nose bearings. Im not sure if maybe removing that could reveal anything. I suppose theres 2 possibilities for a slipping race in the nose. Could be an inner race slipping from the nut not being tightened, or could be an outer race slipping from the nose cap not applying pressure to the outer races properly.
Does the noise and bad finish sound like a preload issue? With no runout and no vibration, i dont know what else it could be. Any ideas on what else the problem could be or how i can pin down what that problem is?