less-than-great sanding results

[Bob Hollingsworth]

Hi, all,

I'm new to this forum but have been turning for ~eight years. During that time I've had precious few projects with really good finishes. My tool technique is good enough (I think!) that I start sanding at 180-220 grit. I typically end at 320-400 and, sometimes, use 00 or 0000 steel wool.

But, in virtually all cases I'm unable to remove all sanding scratches. I'm likely my own worst critic but it seems that almost scratch-free should be attainable. I'm completely willing to accept that my situation is the result of "operator error." I further surmise that I have lots of company in "this boat."

What's the experience out there with Abranet/Abralon, Micro Mesh and Finkat sanding paper/discs? What're your favorite brands? I've used discs from CSUSA, Woodcraft & Klingspor. Since my end result is pretty consistent, I don't think my problem is with sanding product.

What's the concensus on sanding sealer? A woodworker friend once told me that, in his opinion, the sealer seals the wood against subsequent finish products. Is this reasonable?

From what I've read thus far, there's a ton of good experience & advice amongst the forum members. I'd love to avail myself of a little of it.

Thanks much,
-Bob

 

[hockenbery]

Bob,

Sanding the wood to 320 Is sufficient for most north american woods.
You may have more of a problem with your finishing technique than your sanding technique.

Use magnifiers to look for scratches at each grit
When sanding on the lathe use a low lathe speed 300 rpm and high speed on the sand disc rotations.
Have the contact side of the sanding disc move opposite the wood' rotation. You should see a steady stream of sanding dust when the paper is working. If you don't put on a new sanding disc.
I usually do a hand sanding with the grain as the last step to hid any make in the grain lines.

Most of the marks I see on finished pieces I have bend asked to critique or judge (state fair for example) are in the finish not the wood.
It takes a lot of skill to wipe on a finish on the lathe and not leave drag marks. Any wipe on wipe off finish will leave streaks.
Rubbing out the finish or finishing the finish is an essential element in getting a good finish.

I generally do my finishing off the lathe and sand between coats with 400 after the first coat and 0000 scotch brite between coats as they buildup.
I often use a little water when rubbing out the final coat. This cuts back the shine and makes a uniform mark free surface in the finish.
Buffing can be a final smoothing of the finish.

Have fun,
Al

 

[MichaelMouse]

First, line up the proper ducks. CAMI 320 grit is equal to European P400 while 2 out of 3 Micromesh varieties' 1500 is equal to CAMI 400. Neat, Eh? http://www.sisweb.com/micromesh/conversion.htm

Reason for spending so much time discussing grit in this vicinity is that the human 20/20 can distinguish about 300 medium line pairs per inch (CAMI mesh is X/in), regardless the grain structure of wood. What's that mean? Means that if you sand with the grain you can blend your scratches against the background of pores and rings. Sand across grain, and they'll stand out, especially if you press, heat, and burnish their background. All too common with machine sanding. If we can't see lots of dust, we press harder, right? Rotation rate is nearly meaningless except that higher surface velocities allow for more grit passing for each unit of time. Depending on your machine sanding radius/rate differential you may get a different arc length, but an arc is still an arc, and that means cutting across where we want to go along the grain. Which is why we finish along the grain, to blend those arcs.

Certain woods with small, diffuse pores are great candidates for steel wool, which is sort of like thousands of mini-scrapers. On a static piece, it'll do a great job, especially where you have rapid rate of curvature where it's almost impossible to stay straight in line with the grain. Get the wool meant for wood - without the oil, and give it a try.

Couple other methods fool the 20/20 as well. Burnishing heats and contracts the pores, and buffing smooths over the ragged edges grit leaves so that sharp places won't scatter light. You can make a piece glow real nice burnishing with a paper bag or dry (no grease or wax) buffing with a bit of rottenstone or a fine brass brush.

Then there's the final deception - fill the irregularities with a built-up finish.

I like to set up the fuzz on the wood after the first machine passes with 320, take one further round, then set up before sanding along the grain. Reduces the scatter that fuzzy edges make, sort of like buffing.

 

[Gynia]

Good light, magnification, clean the surface with the same solvent that is in the finish you will be using, reversing the lathe for sanding.

Good light and a glancing single point source light (florescent lights are a broad source light) will help you find the scratches before you get to far along.

Inspecting the piece with good light and magnification can help find the scratches.

Using a solvent to clean the surface will also darken the surface briefly which will help identify scratches.

When you turn wood you cut wood fibers and you bend wood fibers over, By reversing the lathe direction for every other grit you can cut the fibers that have been bent over. Of course this will also bend over wood fibers. So reversing the lathe back for the next grit can help solve that.

Starting at too fine a grit can be counter productive as scratches made by the tool can missed.

The one thing for sure is that the scratches become visible as the wood around the scratch becomes smooth. Dropping back a couple of grits can help.

The good news is that as your inspection get better you will also notice that you will change your techniques to limit the scratches.

 

[Steve Worcester]

For this, Finkat and Abranet will work, Abralon and Micro Mesh, I would not go with. Micromesh does not like heat, which on bare wood is ever present. Abralon is more of a higher grit, works better wet type of product. Goes to 4000, but starts at 180, then 360, 500, 1000, 2000, 4000.

If you can see multiple layers of scratches, you aren't spending enough time on each grit. Sure, you can over sand, but is is usually on softer woods with a lot of space between early and late wood in the rings, like maples and ash. What you can try also is sand to 320, then hit it with 360 or 500 Abralon and because it leaves a different scratch pattern, it will highlight any major scratches and burnishes.
Abralon (and MicroMesh in my opinion) are more for oily woods and man made materials (resins and acrylics) you want to sand to a polished state, or for sanding out finishes to the buffing stage.

It really doesn't matter if you go CAMI (US) grit or FEPA (P grit), as long as you know what is what and where they cross over

Here is a handy chart of grits.

Sanding sealer will do a couple things. Providing it is dry, it will seal the wood some, but also gum up the sandpaper. It will only foul the finish of a top finish if it is incompatible with the sealer. So it depends on what you want to do for a top finish.

If you want to try Abranet, drop me a PM and I can set you up with 2" or 3", or any of the products we carry. For that matter, most of us sand paper sellers will do the same for you if you want to try the products.

 

[Bob Hollingsworth]

less-than-great sanding

Thanks much to all who responded. I've gleaned some useful things to try. 🙂

Cheers,
-Bob

 

[Odie]

Bob......you might also consider the use of a random orbital sander. I've found that it helps eliminate the finest sanding scratches for the best defect free surface, with some bowls......but not necessarily all species and/or specific examples of the same species. When it works, it works superbly well, but RO sanding doesn't always give a consistent result. Walnut seems to be one species that tends to always benefit from RO sanding, in my experience........

Others may have different opinions on this, but I don't normally consider RO sanding below 300-400gt paper. The decision to use RO isn't made until it's time to use it, and for the most part, 400gt is the only RO grit I use.

RO sanding can be done powered up on the lathe, but unless you can do very slow variable speed (about 25 rpm), then the best way is to rotate the bowl by hand on the lathe while RO sanding with the other......

I have the Grex 2" RO sander, and have been happy with it....... would not do without it!

Because Random Orbital sanding doesn't always produce an improvement, a turner will have to develop a "sense" about when, or when not to use it......but, it never hurts to give it a try! The bottom line: When RO sanding improves a specific finish, the results are spectacular!

ooc

 

[Dave Ogren]

Sanding

I get the best results with my angle drills at a fairly low speed. Removes more wood per sheet and doesn't generate heat that will kill the hook and loop.
Good Luck,

Dave