-What's causing the Headstock to hum

It doesn't know the words. Sorry, I couldn't resist

Man! You should put up a spew warning next time.... I got iced tea all over the monitor that time!

Check the belt cover. I've had the same prob on 2 different lathes. If tightening the screws doesn't fix it, try putting thin neoprene or fiber washers between the cover and the lathe.

I was going to say maybe your headstock bearings are just a tad too loose. When your tool gets to the outer diameter of a piece, even if you are using the same amount of force as you did towards center, that force is amplified by leverage and putting more sideways pressure on the spindle causing the bearings to vibrate. But then I thought some more, and figured it could be the wood itself humming. Probably due to the thinness of the wood, it's hardness, and the broad-edged scraper. If you heard the humming while turning the outside (before hollowing) my first theory makes more sense. If you find a way to adust your bearings, do so very carefully--a bit too tight can overheat and wear them prematurely. I could be wrong on both points, it may be just the quality of the lathe--but with those cheap imports, you can usually tweak them for better performance if you have some mechanical know-how.

Thanks to everyone for their comments. Maybe the situation would have been better depicted by using the "Harmonic vibration " instead of humming noise. After about one week I have found that all the comments are valid. The Harmonic vibration is probably produced by the unbalance in rotating components of my lathe. This may be further compounded by resonance caused by shattering of the scrapper applied on the thin wall of the maple bowl. I was told that in some instances the rotating components may be fairly balanced but the finishing gouge or the scrapper lightly rubbing on a bowl could produce resonance. I was told that the same thing takes place when rubbing the lip of a glass with your finger. Some time bowl steady are used. Now, If only I can find a way to adjust the bearings I may reduce the Harmonic vibration a little?

If it were my problem, I'd run the lathe empty and use my stethoscope to listen for bearing rumble. You may also do the old mechanic's trick by placing the steel end of a screwdriver on or near the bearing cap and the large end butted up to your ear. If there's interference at all - repeating change in pitch - then you might consider adjusting preload in accordance with your instruction manual.

That said, I'd bet it's just plain old flex and chatter. A cross-grain bowl presents two mutually reinforcing problems when a scraper is used. First is the natural deformation of the bowl as you exposed and dried the damper interior - bowl will be narrower across the face than along the long grain. Second is flex as the bowl tries to get away from the scraper. That bit of tearout that you see as you pick up the unsupported ends of the fibers makes the bowl squirm away. The combination often produces chatter marks, always produces noise.

What to do if it's natural? Change your scraper angle to get a bit more shear, or go back to a broad nosed gouge and cut/shear down slope not outward . In either case, don't be anxious to get the wood off. Just take the mild cuts and keep the speed low, and the chatter, if there, will be minimized. A bowl steady will allow you to get much thinner, but I find somewhere around 7mm to be the point at which chatter becomes inevitable on a 12" piece.

Thanks for the information George I have used a screw a screwdriver near the bearing cap. The noise is constant without any change in pitch.

Lately, the heating system in our house is working hard to cope with extreme cold weather (-30). The blanks are stored in between the basement rafters. When turning the blanks I noticed that they are very dry. I only hear the low pitch noise when I take light cut/shear with the scrapper.

Sounds like it's the natural result of increased friction and a grain lift or two. Are you getting chatter marks on the surface?

Couple things I've done in the past, before a steady, is to turn slow and ride the left hand outside the bowl, or take two or three rounds of duct tape to the outside to dampen vibration.

I burn wood, myself, and I've been obliged to stoke four times a day with what our temps have been - negative 20's Celsius. Of course the wind blows, the lake snows, and I've had to plow pretty much every day for the last week and a half. My frozen wood supply is under a hard-packed 66 cm of snow, which is what two meters of light stuff compacts to.

I swear the road commission has a sensor at the end of my drive. Every time I remove the snow, they come by with the plow and fill in!

==================================================== You need to come on down to central or south Texas for the winter. Here (near Austin) the low so far this winter was this week at +21 degrees F. Tomorrow is supposed to be about 60 and sunny. Down near the border, it's even warmer.

Ken Moon Webberville, TX

Are you getting chatter marks on the surface? Before the dried blank gets trued. If I am not careful with the scrapper and use too much pressure I do get chatter marks. When I use a gouge to true the bowl I do not get charter marks. Once the bowl is trued. Using the scrapper again removing less than paper thin wood. I get a finish of about

Are you getting chatter marks on the surface?

With those temperatures I would think you would get chatter marks.

Martin