I have a G0704 with AC bearings and a DMM servo spindle motor using Hoss' timing belt drive conversion currently running at 5000 RPM max. Eventually I'd like to get 7500 max for smaller tools, but that's down the road from now. My issue is that even anything over the stock RPM, gets quite noisy. A little bit of noise is alright and expected, but below I'll put of video of what I'm currently experiencing. It's ~60dB ambient noise and ~98dB with it running just at 3500 RPM (which is what I'm limited to until I have a 240v outlet installed for the spindle motor). I've tried with and without the little adapter that goes between the splines and the top portion of the quill with no noticeable difference. FWIW I also used one of those vibration apps to check it and at 3500 it actually wasn't too bad.

I've heard timing pulleys are often the cause of this. I'd like to try the Poly V-belt ribbed pulleys, but I can't seem to find them as easy as I could find the timing pulleys that were on SDP/SI. I'd make them myself, but I don't have a lathe so I can't really do that. Is there a good source out there for these pulleys? If it's somebody who can do custom bore sizes on the cheap too, that's a bonus lol. If not I can just bore it out myself but I doubt it would be as concentric.

Another thing I've heard is that bearing preload has a place in this. I also tried different preload settings, loose, medium, and rather tight with no difference in noise. I did notice that I can't seem to get a perfect balance of preload though, if It's too tight it doesn't move smoothly (obviously) but if it's not tight there's a very small amount of axial play. I think I can work around the axial movement though because if I (when installing the pulley) hold the bottom of the spindle upwards then seat the pulley at the lowest it goes it takes out that slop. Probably not the best way but it seems to work.

https://drive.google.com/open?id=14s...dP0d53YG3DJIpv