Banding on finished bowl

[Rob Miller]

I just turned a hickory bowl. I sanded with 80, 120 and 220 grits using a power drill with a padded disk, then 400, 600, 800, 1500, 2400 and 3200 with paper/cloth by hand (spinning). I thought it looked pretty darned good until I decided to dye the outside of the bowl a cinnamon color. Then it showed considerable banding from the sandpaper. I'll redo it after I can get a longworth style chuck, as I can't remount it now that I've severed the tenon. In your collective experience, would the use of a sanding pad instead of fingers help to resolve this problem? There are areas I couldn't reach well with the drill sander and I didn't have a full range of grits for that tool.

[John Keeton]

Rob, I know there are folks that sand to those ultra fine grits, but it is rare when I sand beyond 400 and I have no difficulty in getting excellent surfaces. Normally, I would start at 150, as 80 grits scratches are difficult to remove, but if you need to so that (and, we all do at times!), then spend the most time at 80 grit with very moderate pressure and constantly moving the sandpaper. Let the paper do the work, not the pressure. Then, spend nearly as much time at 120, if that is what you have. In what you are using, there are a couple of gaps that may be causing you problems. 120-220 is too much, as is 220-400. My grits are 150, 220, 320 and 400. From there, and usually only on Blackwood finials/pedestals, 600, 1200, 2000. I have never seen the need to go beyond that. On holly finials/pedestals, which I use often, I sand to 1200 usually.

My guess is that you have some 80 grit scratches that are much deeper than you thought and dyeing anything will quickly show the sanding marks! You have learned a valuable lesson on that.

[Lloyd Butler]

The other thing to look at is to try sanding with the grain before moving to the next grit. As you get finer and finer, you may end up burnishing the wood more than sanding, and if you are going across the grain, then applied a finish, you can get blotching or areas where the wood is burnished more than others and the finish will not look good.

It does not take much to sand with the grain to help get rid of cross grain scratches. And as John pointed out, try not to take too large a gap between grits. A first guess at the grits is to not go more than 1/2 of the previous grit, to the next grit. 80 -> 120 (80+80/2) -> 180 (120 + 120/2)-> 220 -> 320 (220 + 220/2) ->...

Once you get above 220, the standard grits available may not match the 1/2 steps very well.

[Rob Miller]

The other thing to look at is to try sanding with the grain before moving to the next grit. As you get finer and finer, you may end up burnishing the wood more than sanding, and if you are going across the grain, then applied a finish, you can get blotching or areas where the wood is burnished more than others and the finish will not look good.

It does not take much to sand with the grain to help get rid of cross grain scratches. And as John pointed out, try not to take too large a gap between grits. A first guess at the grits is to not go more than 1/2 of the previous grit, to the next grit. 80 -> 120 (80+80/2) -> 180 (120 + 120/2)-> 220 -> 320 (220 + 220/2) ->...

Once you get above 220, the standard grits available may not match the 1/2 steps very well.

Actually, it could be burnishing I'm seeing -- perhaps from areas of the paper where the grit has become worn away. I can't actually feel the scratches, so that's a possibility.

[robert baccus]

I do 95% of my sanding with power sanding. Electric on the outside and inside(long mandrils) and small air HF grinders on the inside also. I only go to 220 if I use a film finish. Machine sanding does not leave parallel grooves like a LP record. And like above use high RPM but very low pressure to avoid scratches. Even 80 grit leaves few scratches at 8000 rpm and low pressure.

[Bruce Pratt]

Picture would help diagnose the problem.... Does the banding go all the way around the bowl, or is it just in a few spots. e.g., just before the end grain? Instead of a sanding problem, your may burnishing/crushing the wood with the bevel on your chisel.

[John Grace]

Rob...I too struggle at times with sanding marks (and the occasional tooling mark, ughhh). Question...do you have an idea how much time you spend with each grade before moving on? That may help offer guidance on whether or not your burnishing versus sanding. As others have also suggested...I use a small electric pad sander on the coarser grades as that dramatically lessened marring. From there, I hand hold the finer grades...agreeing with John K. that the final grades being left mostly to what the wood, the piece, and personal preference dictate.

[Reed Gray]

There are marks that you can pretty much cover with 400 grit, but when you go past that, there are some that come to the surface. The ultra fine dust will get into those spots and high light them. I just wipe the piece with my hands, which removes the surface dust, but leaves the stuff in the lines. Mostly tear out I think. Other than that, you are not getting out ALL of the previous marks/scratches before going to a finer grit. Maybe you need good prescription glasses. Maybe you need better light, which to me is the most common one. Take the project out into direct sun light, and you can be horrified. I use Blue Max lights, which are a full spectrum bulb, and are almost as good as natural light. Ott lights are another brand. Blue Max did run an add in Woodturning design some years back.

robo hippy

[Rob Miller]

There are marks that you can pretty much cover with 400 grit, but when you go past that, there are some that come to the surface. The ultra fine dust will get into those spots and high light them. I just wipe the piece with my hands, which removes the surface dust, but leaves the stuff in the lines. Mostly tear out I think. Other than that, you are not getting out ALL of the previous marks/scratches before going to a finer grit. Maybe you need good prescription glasses. Maybe you need better light, which to me is the most common one. Take the project out into direct sun light, and you can be horrified. I use Blue Max lights, which are a full spectrum bulb, and are almost as good as natural light. Ott lights are another brand. Blue Max did run an add in Woodturning design some years back.

robo hippy

Are you coming to the Symposium this weekend? Maybe I'll just bring the bowl and get your thoughts.