You've probably already tried, but if not, release the belt tension completely and turn the spindle by hand trying to feel if there are any little bumps or catches or points of resistance, or even what feels like a smooth excess resistance to turning. Little bumps of resistance could mean either debris in the bearings, or brinnelled bearing races. Excess smooth resistance could be caused by too much preload on the bearings. I would expect that the new bearings and seals of the newer lathe would require more effort to turn than the older machine, but not an arm tiring amount.
Another you've probably already checked, are the motor and headstock pulleys correctly aligned? Misalignent of the pulleys can cause strange noises as the belt trys to walk. Pulley setscrews tight? Is the rpm range that the noise occurs in an area of range overlap? If so, does the noise occur at the same rpm in both ranges?
Hearing the noise would be a big help in coming up with ideas.
Not knowing the details of the assembly, and assuming that the headstock uses a pair of tapered roller bearings or angular contact ball bearings;
With a medium weight wooden mattet, and the lathe running at the speed that causes the noise, give the end of the spindle a light to medium axial tap on first one end and then the other. Do not bash it to the point of causing bearing damage, and do not tap it with the spindle not turning. It could be that the bearing races have a bit of misalingment in the housing, and tapping things will help seat them and quiet the noise.
Another thought, put a block of wood between the spindle and tailstock with only sufficient pressure to retain the wood, and bring the rpm's up to the point that the noise occurs. Let the lathe run for an extended period of time (several hours) in this condition. The extended running will warm the spindle bearings and spindle up more so than the housing, causing a lengthwise expansion and possibly correcting any race misalignment issues during the expansion and subsequent cooling contraction.
If the tapping or heating and cooling does make a slight correction of the bearing seating and quiet things down, it may be neccessary to check and/or adjust the preload on the bearings.
Later,
Dale M
Dale,
All good suggestions, and it sounds like you are a lot more knowledgeable than me with machinery. I am handier with wood than bearings and such.
There are two new spindles in question, and both sound about the same altlhough they are from the same batch (both have wonky threads, for example). They turn very smooth to the hand, although a touch more resistance to turning due to them being new (old ones have may thousands of hours on them). And both bearings in each run slightly warm at speed which seems like a good sign.
I haven't run it for long periods with a block between centers, but I did do that a bit and the sound itself was similar the same either way although very slightly worse with pressure from the tailstock. I'll try it for longer. I have run the latest spindle (the one I got the threads doctored up to run chucks true) off and on at various speeds and reverse for probably 6 or 8 hours total and the sound is not improving (actually it seems to be getting louder but I can't be sure).
In terms of dealing with actual preload, I am not equiped to do that. The way the 2436 bearings come the preload is determined by spacers in the inboard headstock cap which comes already bolted to the spindle on that end. The outboard bearings are designed to float back and forth in the outboard carrier with heat expansion. For whatever reason, when I loosed the outboard and endboard headstock cap bolts while the lathe is running, the sound is slightly better. Might just be because the sound is not as well transmitted to the headstock for amplification, I don't know.
In terms of the pulley alignment, that was something I tried to figure out from the start. Can't really see clearly if they are aligned perfectly, but they look close. I did notice that on the last two spindles, the pulleys are in slightly different positions relative to the bearings as compared to eachother. About 3/8 inch.
In terms of overlapping pulley ranges, that is something I tried way back when and I just went out and tried it again to make sure. The sound is the similar at say 1800 rpm either the middle or high pulley. I have compared sounds so many times now that small differences get harder to be definite about.
I probably should get a stethoscope and try to track it down more, but I've already spent about 20 hours total messing with the problem over the 5 months (and many more hours thinking about it whether I wanted to or not) and I don't have enough time to fool with it much more. One more thing I will try later today is to switch complete headstocks again between lathes and listen really closely. I don't expect that to be different than before, but maybe I could learn something about the sound.
I am told that Oneway went to double spindle bearings a while back and I can't help but wonder if that changed the sound. Doesn't seem like it should. But even with a new headstock and spindle complete, it doesn't sound anything like my older ones at higher rpms.
I am probably going to record it again this weekend with a camera video, but it's hard to hear much on small computer speakers. I did record the first spindle, which I believe was the loudest of the three spindles but Kevin said he couldn't tell the difference between lathes so I am not sure the vid is helpful.
If you are curious, that recording trying to show Kevin a difference between the sounds of the old and new lathes (and not particularly well I guess) can be seen the link below. Any feedback is welcome. The difference between the two different sounds is much more noticeable in person in part because of the way small cameras tend to automatically adjust down louder volumes, as vistors to my studio can attest. They have agreed the second lathe sounded awful. Someone pointed out I am trying to talk much louder at the second lathe, and I am going to try it again with a small radio on the lathe that will produce a steady sound. On the first lathe the radio gets harder to hear of course, but with the second lathe the radio gets competely drowned out.
http://www.youtube.com/user/VesselMaker#p/a/u/1/0Z-8npb9wbM
I generally turn with earplugs, and with my oldest lathe basically I just hear the wood being cut and background whirring. With the second lathe even with the new spindle, I am very aware of the noise from the spindle and can't really get into my happy place.