Sandpaper

[Chris Gilbert IRL-1638]

Hey Sparky,

Any chance of a summary of sandpaper use? Don't get me wrong, I'm not trying to be smart, but you said in a recent post on your T Bolt you's used quite a few bucks of sandpaper on the machine.

I'm a novice, and my building skills will probably never rival yours, but I can dream of that perfect finish. I also appreciate that a large part of the finish is the elbow effort of sanding the airframe.

What grades of sandpaper do you use, and for what part of the build process do you use them?

Thanks

[RC Storick]

Some think I am to aggressive in sanding. I start out with 40 grit to rough in the wood. Then drop to 80 to get the shape closer. Drop to 180 while shaping. Followed by 220. Just before starting to finish I completely sand the AF with 400. Apply dope sanding between coats with 400-600. After clear I use 1500 followed by 2000. Allot of elbow grease will yield a great finish.

A light finish is done with clear dope only as a primer. You only want to fill the grain. So apply a couple coats and let dry. sand down to the grain and follow the process all over again. Final coat is when the grain just frosts over. Now your ready for color.

Sanding is an art. A good finish is not whats put on but what is removed.

[Keith Spriggs]

I have done more sanding on cars than it would take for a thousand models, however the principle is the same. Bob has summed it very well, however I thought that it might help if I explained the process that takes place. The sanding serves two purposes first is to level the surface and the other is to smooth the surface, the smoothing is actually a continuation of the leveling process. If you use the wrong paper for either part you are going to have trouble. The grits that Bob uses are OK (not surprisingly).  To straighten the surface you need as coarse a sandpaper that you can use without gouging the material to deeply. 40 grit used carefully and with a block would quickly and properly straighten the surfaces. As you go to finer grades the object is to maintain the straightness of the surface at this point smoothness is not the primary object even though it will of course get smoother. The last stages are for smoothing. Even at this stage you must use care to avoid oversanding in one area and causing a low spot. If you have done everything correctly after you have applied the last clear coat and sanded with 600 the model should be straight and very smooth. Finishing from start to completion is a process of removing low spots without creating new ones. Even when you are sanding with 2000 grit you are removing the low spots caused by the grit in the 1500 paper. A good finish whether it is on a car or an airplane is a lot of work and very rewarding. I have never found any shortcuts or any way to skip a stage.

I hope I have not confused the issue more than clarifying it. I guess I could sum it up by saying that from start to completion it is a process of leveling. First the irregularity's in the wood with the 40 and then the marks made by the 40 with 80 and so on to the final finish. Remember if you skimp at any stage the low spots or sanding marks that are left will not likely be removed by subsequent finer grades.

[RC Storick]

I have done more sanding on cars than it would take for a thousand models, however the principle is the same. Bob has summed it very well, however I thought that it might help if I explained the process that takes place. The sanding serves two purposes first is to level the surface and the other is to smooth the surface, the smoothing is actually a continuation of the leveling process. If you use the wrong paper for either part you are going to have trouble. The grits that Bob uses are OK (not surprisingly).  To straighten the surface you need as coarse a sandpaper that you can use without gouging the material to deeply. 40 grit used carefully and with a block would quickly and properly straighten the surfaces. As you go to finer grades the object is to maintain the straightness of the surface at this point smoothness is not the primary object even though it will of course get smoother. The last stages are for smoothing. Even at this stage you must use care to avoid oversanding in one area and causing a low spot. If you have done everything correctly after you have applied the last clear coat and sanded with 600 the model should be straight and very smooth. Finishing from start to completion is a process of removing low spots without creating new ones. Even when you are sanding with 2000 grit you are removing the low spots caused by the grit in the 1500 paper. A good finish whether it is on a car or an airplane is a lot of work and very rewarding. I have never found any shortcuts or any way to skip a stage.

I hope I have not confused the issue more than clarifying it. I guess I could sum it up by saying that from start to completion it is a process of leveling. First the irregularity's in the wood with the 40 and then the marks made by the 40 with 80 and so on to the final finish. Remember if you skimp at any stage the low spots or sanding marks that are left will not likely be removed by subsequent finer grades.

What he said.

[Chris Gilbert IRL-1638]

Guys,

Thanks for that. I think I'll print it out and hang it over my building board.

Too late for this model, but not for the next one......

[Bill Little]

Use a sanding block or fixture of some type at all times to get the airframe to the point of applying the finish.  Even afterwards as much as possible.  I make sanding "blocks" of all sizes and shapes for particular shapes.

[Keith Spriggs]

Use a sanding block or fixture of some type at all times to get the airframe to the point of applying the finish.  Even afterwards as much as possible.  I make sanding "blocks" of all sizes and shapes for particular shapes.

Good advice. I hate to keep referring to cars but I have had much more experience with cars and the principles are the same and you basically use the same process for either a car or any other item that you want a superior finish on.

As Bill stated use sanding blocks whenever possible. I use a sanding block all the way down to 2000 or even 2500.  Use a sanding block that is large as possible for the area involved. I use a hard rubber sanding block with some very thin foam or thick absorbent poster board between the block and the paper when I am sanding with last few grades of paper. One more thing use good quality paper and change it often. When the grit on the paper gets dull or filled  it no longer cuts and is an invitation to problems.

[Will Hinton]

Hi Y'all,
I build custom guitars as a vocation and the "What he said" comment above is right on.  However - I have discovered a new product I have come to love that helps on the final stages of sanding the surface level.  The notro-cellulouse lacquer I use for my instruments is very similar to non-taughtening dope and will gas off & shrink for up to six weeks.  There are places on an instrument where block sanding is impossible, like the backs of necks, etc., just as on the certain curvy places on a model without special shaped blocks.  I no longer make those!  I use a product from Sandman Abrasives  (Google them) that is fine grit on medium to dense foam for these areas, and I even use them for patching in repairs on flat surfaces.  They work GREAT!!!!  No blocks needed and very fine results.  The intro pack has 2 ea 600 - 800, 2 ea 800 - 1200, and 2 ea 1500 - 2000 grit pieces in it for around 7 bucks.  I highly recommend them.  One word of caution; they cut more like a lower grit but leave the surface as though they are truly the grit listed.
Blessings,
Will

[Bill Little]

On the "sanding block" theme:  I make a lot of "blocks" to suit various special needs.  Bob Hunt fired up this poor old overused brain years ago when he turned me on to the uses of the foam that makes up the cradles of foam cores.  Plus the "hard" foam that is often used in packaging.  it's all "free"!  You can use th efaom friendly 3M contact spary on one surface and stick the paper to it then peel it off if necessary.  Yes, as Keith says, sand paper DOES get dull.  Lacquer is a "hard" paint when it's cured (dope is a lacquer) so a lot of sandpaper gets dull quicker than we think.  If the paper is cloggin (dope is balling up on it) then you need to let it cure longer.  When it's fully cured it will powder off.

And get GOOD high quality sandpaper.  I like the various 3M "grades" that I get at the auto paint supply.  All the way from 40-??  I think the highest around here is 2500.  Plus they have some types that are "sticky backed" that come in VERY handy.  Remember, you are "scratching" the finish and each higher grit makes tinier scratches and takes out the deeper scratches.  Keep going to finer grits as long as you can stand it! 

I used to do a good bit of auto painting, and it's all the same as to getting a "flat" surface which is what we're really after to get a high gloss, and it starts, as Robert says, "with the first piece of wood cut (sanded)!"

[George]

So far, most of the advice applies to finishing a painted surface. No one has touched on the types of sandpaper such as flint, garnet, silicon carbide, aluminum oxide, etc.

Some can be used wet or dry while others can only be used dry. What about the "no fill" sanding sheets?

Do some use the same type with just different grades?

For instance, I use garnet paper or aluminum oxide as the course, medium, and fine for bare wood. Then switch to silicon carbide for the finer grades (above 220) and for wet sanding. My 1000-2000 grades appear to be silicon carbide but it does not say so on the package (3M Imperial Wetordry).

George

[Bill Little]

Hi George,

I guess you *could* say that I was referring to sanding a pained surface, but I do the same from bare wood.  A snding block from the first pieces. 

I also have belt sander sheets cut and applied with double sided golf grip tape to th eedges of my table.

I only use automotive sandpaper anymore, except for the Emery cloth and "Plumbers Cloth" (which is rolls of emery cloth about 180 grit and about 1" wide) which is great for evening out curved surfaces..

Being "cheap", I buy it by the sleeve when I have enough extra money to do so.  It's cheaper that way.  I also use golf grip tape to attach strips of sandpaper to my Great Planes long sanding blocks.
Bill <><

[Mark Scarborough]

Another excellent choice for grits up to about 320 is rolled paper. It comes on a roll that is 2 3/4 " wide and is already adhesive backed. simply unroll what length you need, crease and tear it, then affix it to your block. I love this stuff cause when sanding a wing witha 24 inch or longer block you dont have the seams that can catch and drag a scratch into the surface like when joining segments of normal sheets on a long board. It is also great for those custom sanding blocks with curves and such.It is the only paper you find on my building bench coarser than 320. Above 320 I use sheet

[Keith Spriggs]

Another excellent choice for grits up to about 320 is rolled paper. I

I couldn't agree more. I have made up sanding blocks up to 4 foot long for special purposes. Another handy use is to stick it to a flat surface and then rub the work piece on it to flatten it. I use the table saw top.