Making Bowl bottoms flat ?/

If you mean that you FORGOT to turn the bottom before you finished the bowl, I would suggest laying off the booze until you have finished in the workshop:)

If you mean that what appeared flat when it was on the lathe, but looks rippled when it is polished, then I can sympathise with that. I recently turned a very shallow artsy piece which is basically a platter. I thought it was flat across the 'platter' surface, but a few coats of danish and a good buffing prooved otherwise. Flat surfaces are tricky.

More care and attention is needed. Maybe offer up a straight edge. Maybe polish it with fine abrasive and shine a light across the 'flat'.

I am guessing though that your problem is the base that the bowl sits on. I think the best solution is to dish it out somewhat, or decorate it by some means. I don't find totally flat bases aesthetically pleasing.

Large flat surfaces such as on flat platters or plates are a challenge without a doubt. I use a straightedge but that won't necessarily catch the very small waviness that shows up when finished. You can try shining a light on the surface at a shallow angle and your sense of touch can be a help. If you can feel it you can see it - note these are also drywall sanding techniques as well.

I find that power sanding is better than hand sanding. If you are also referring to the bump that appears in the center of bowl bottoms, I find power sanding to be a great help since there is sandpaper "movement" produced by the turning disk. When you hand sand in the center there is very little movement since the workpiece radius is very small which means you remove less material at the absolute center and increasingly more as the radius increases for a given application of the paper. Billh

Wood moves and if you don't allow for it you are saking for trouble. A flat bottom is a no- no. The piece should sit on a foot which is distinct and the rest of the bottom should be concave so as to clear the table or whatever.

Now, that will almost get you there. Even if the wood is perfectly dry when you finish the bottom, because you are removing wood which may relieve stresses in the wood which is left, you need to take one additional step. Make yourself a sanding block maybe 6" x

6" and glue some 220 or so to it. After the piece has aired for a little while (maybe the next day) rub the bottom on the sanding block to re-flatten it.

Then if it moves, you have done all that you can do...

Bill

What Bill said, except that you may have any bottom contour you like, not necessarily what most call a "foot." As long as you begin with a relieved -concave- area at the bottom, you can wait a week or so and either drag it over paper or run the block over it. I keep some stickyback paper adhered to a tabletop to get a flat seat for bowls turned green to finish contour.

If you're having these problems with bowls you think were dry, have a bit of patience and dry them longer. Unless you've got some truly thin bottoms, the wood will adjust along the lines of least resistance as you scoop it out - the thin end grain above.

flat bottom is a no-

bottom should be

when you finish the

wood which is left,

6" x 6" and glue

the next day) rub

Derek No not the base that it sits on. That I concave in slightly. The interior of the bowl i,m refering too. I don,t like all my bowls that concave in ( on the inside ) but some that seem perfectly flat when i,m finished are not when the finish is applied.maybe a flat edged plastic ruler would give me a good indication before i decide there finished.

Keith

when I visualize trying to get a bowl (what size are we talking about?) totally flat inside, I wonder how you are doing the transition from bottom to side. That is particularly hard to sand. If a bowl is wide enough, then yes, a small straight edge could help, but if you look in your cupboard at the various metal, ceramic and pottery bowls, you won't find many with a 'flat' bottom because even a small curve makes them easier to work with.

If you are determined to achieve a certain 'look', just make several wooden blocks of various widths that you can use as small straightedges,,,

SNIP ...

=========================== If you do the above and put some adhesive back sand paper on each one, it will help achieve that flat you're looking for.

Ken Moon Webberville, TX

Keith,

I believe I would be trying for a curved inside bottom, rather than one that is tabletop flat. Curves are inherently more pleasing to the eye. Of course, not all curves are pleasing. It takes some work to get just the right curve. Flats simply are.......well, boring.

Also, as you have discovered, absolutely flat surfaces are very hard to come by in woodturning. I vote for curves!

Just think how unappealing the "other gender" would look if composed entirely of straight lines!

Barry

What Barry said, especially about the opposite gender. Or the same, in our PC society. (Keep yer shorts on, Anonymous Bill, it's meant to be a joke)

The other reality which may be causing you problems is that of the wood grain itself. If the grain is nearly parallel to the desired bottom, rather than _absolutely_ parallel, you will have one or more transitions from light, easily sanded early wood to the denser latewood, which comprise the annual rings. This reality is one Bill and Ken have suggested compensation for, without mentioning the cause.

This unequal density phenomenon can visually ruin even modestly curved bottoms, which is why I like to use the Power-Loc semirigid disks to clean up gouge marks. They bridge irregularities better than flexible backings, helping me maintain the fair curve I (hopefully) cut, or improving to it by taking the proud spot down without touching the low. I sand with the shaft supported on the rest, so I can do what we do with a gouge and reference even a flat by using my finger on the rest as a gage. An additional benefit comes with spalted wood, or designs with interruptions - the more rigid disks bridge, rather than dive into holes or soft spots, avoiding frustrating blending later on.

There is another solution to flatter bottoms, but it takes some big timber. If you cut your blanks to hollow opposite the curve of the annual rings, or quartered, you will get smaller, more bridgeable areas of softer wood on a flat bottom.

The most recent issue of Woodturning Design has an article on getting a perfectly flat surface on a platter. After using a straight edge to get it as flat as possible, the author power sands. Before he sands though, he makes some radial pencil lines and gives a quick sanding, this will show the slight ripple remaining. I don't have the article with me, so I might not have it 100% right. Martin