Denis Marier wrote:
My lathe is a low end Taiwan made with 3/4 HP and 1” 8 tpi.

The other day I was finishing a 9” OD maple bowl with a 3/8 X 1” scrapper at
about 800-1000 RPM.
It worked well. Until I reached the 9” OD lip where the wall thickness
was about 3/8 thick. Then what seem to be the Headstock started to hum at
low decibels.

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.


--
Ken Grunke
SW Wisconsin
http://www.token.crwoodturner.com/
Member, Coulee Region Woodturners AAW chapter
http://www.crwoodturner.com/



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