In message cTyNj.137$og.91@edtnps91, Darrell Feltmate
writes
Bob
Welcome to the group and to turning. Thanks for the kind words on the web
site.
You have dicovered one of the bug bears of wood turning, leaving "ruts" or
grooves in the wood. It takes ages longer to sand out a groove than to
remove a rib or ridge. The trick is to practice. No surprise there I
warrant. There are two ways to prevent a groove; you have already found a
cure with scraper and sand paper.
1) A long gradual cut from outer edge to the center of the bowl. He who
hesitates is groovy :-) I like to do this with an Oland tool with long edges
or a bowl gouge with Irish grind. I hold it parallel to the ways with the
point of the tool leading and cutting just behind the point. I am NOT
riding the bevel although others do a similar cut with the bevel riding. The
cut proceeds to the center or close to it.
2) Using the same tool make a cut from edge toward center with the bevel
rubbing. If you can go right to the center, but in most cases the bevel need
changes so fast that about two inches can be cut at a time, then the hands
need to chage position. Watch the ridge left behind to begin the next cut.
Ideally it rides the bevel into the waste wood at exactly the same level and
the last cut finsihed. If not ideal, enter a hair above the last level, not
below it.
These are finish cuts with a freshly sharpened tool and little pressure,
aiming for fine shavings and a good surface, not fast wood removal.

To get rid of that nubbin in the center, I like a scraper, either flat or
slightly curved. If the wood tears easily sandpaper works great. No shame
here.

I would add one additional item to check. If the tool rest is not smooth
it will make it difficult to slide the tool smoothly and each stop is a
potential rut, OK that's what I found
--
John