: First, you can't skip grits. If you start with 40 you need to go to
: 60, 80, then either 100 or 120, then 150 or 180, then 220.
: Hitting them each wouldn't be overkill. If you do this each grit
: will be able to work the way it's supposed to, and it will
: actually take less time with each successive grit.

On hard materials I agree.
On cedar you can skip one grit ONLY if you soak down the wood to raise the grain.
On epoxy I'd use 60, 80 then 120.
I'd only use smaller grit changes on steel.

120 grit
: isn't intended to take out scratches left behind by 40 grit
: paper.

YES, 40 grit jump to 120 is too great a step.

As Rob said, sand paper works best with light pressure.
: Using the right grit lets you use light pressure. Skipping grits
: makes you more likely to end up with unsanded or rough spots
: when you get to it.

Light pressure allows the ROS to spin at a higher speed which makes
it cut more aggressively. Try turning the ROS on while you hold it above the wood
surface and let it speed up, then bring it in contact with the wood you'll see how fast
it cuts before the disk slows from downward pressure. If you work with a light touch
and even lift the ROS off the wood occasionally, it will cut faster.

Also- sandpaper is an edge tool that needs
: to be sharp to work, just like a plane or a knife. When it gets
: dull it doesn't work right. Keep it fresh, and throw out
: marginal paper. Don't wait for it to get so dull it feels
: smooth.

Yes change paper often. Get a feel for how new sharp paper cuts, so
you know when it's time to change.

: As others have said, a random orbit sander is the right tool, but
: it is my opinion that before you hit the ROS, you need to use a
: long board to fair your hull. Any sander can only fair as wide
: as its disc, otherwise it will follow the contours of the boat.
: For a ROS you're talking 6". I generally use an 22"
: long board. I start with 60, but don't use a ROS at 60 because
: it's too aggressive. It's easier to make mistakes than using a
: long board.

How do you "fair" a fair surface?

This is what strip building is all about!

A clear straight grained strip of wood naturally produces a fair curve when bent.

If you align the edges of each strip with the previous strip edge
and your strips remain in contact with the stations and stems
the result IS A FAIR SURFACE!!!

How do you fair a board that's been run through a surface planer?
You don't, because it's flat and fair.

If your strip edges aren't aligned, if your bead and cove edges aren't flush,
if you use 1/4" thick strips you can't bend or twist to the proper shape, if you
use butt joints, and if you use a stapleless stripping technique that doesn't
keep your strips attached to the stations and stems, you will have an irregular
surface, and if you destroy it further by planing, I agree, it must be faired.

However, If you align the edges of each strip with the previous strip edge
and your strips remain in contact with the stations and stems
the result IS A FAIR SURFACE!!!

You don't need to fair a fair surface.

This idea that you must fair the surface of a stripper is passed on from fiberglass
boat construction where repairs must be faired. Auto shops have to fair surfaces
where fillers have been added.

A properly built stripper does not need fairing. The ROS will follow the fair surface and
keep it fair IF you work on a small area, say 12" square, move the ROS in circles to follow
the curving surface, and KEEP YOU EYES FOCUSED ON THE SURFACE TO SEE the change
from a rough irregular surface to a uniformly sanded one and immediately move on to the next
area. Doing this ensures you've taken down a even amount of wood and keeps the surface fair.

This is TOTALLY dependent on your keeping a constant visual assessment of the progress of the
sander. If you are thinking about something else, multitasking, or otherwise not completely focused
on the visual transition of the surface, from rough to smooth then it won't work.

I've seen people sanding where their just moving the sander back and forth, going all over a large surface
in a random manner, staring off in space, because they don't have a clue as to what they're doing. They
just want it to be over, so it's three passes with this grit and three passes with the next grit and they
wonder why scratches show up later.

: Time and patience are the most important steps in good sanding.

Yes, it's time, patience, and acute visual focus.

: Lastly- there's an article on sanding in the latest Fine
: Woodworking:
: http://www.finewoodworking.com/SkillsAndTechniques/SkillsAndTechniquesPDF.aspx?id=34628
: You may also want to look into how auto body shops do their
: sanding. It's the same process as fairing a boat.

There will be similar techniques but each discipline will have unique characteristics.

In furniture building it is assumed your wood stock will be joined and thickness planed
which will mean you will never sand a surface with sandpaper courser than 80 grit.

In strip building, wood strips will most often have a sawn surface which will require sanding
to level this irregular surface with a courser 60 grit. 60 grit on a ROS will level the surface
of cedar quickly and uniformly using the flat fullest surface of the sanding disk. 80 grit
will not level the same surface as quickly and uniformly and will naturally lead the worker
to use the more aggressive edges of the sanding disk in what I call "eraser" sanding which
will destroy a fair surface.

For full details of my ideas on sanding and maintaining a fair surface see "Learning How to Sand"
on my "Shop Tips" page. http://www.laughingloon.com/shop.tips.html

Rob