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Model Builder's Guide to Selecting Sandpaper

May 05, 2015



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Airfield Models (http://www.airfieldmodels.com)Sandpaper and Sanding Blocks

I can not stress enough that the most important tool for achieving a quality finish is sandpaper.  For whatever reason people convince themselves that sanding is too much work, too tedious, too time-consuming or have some other invalid excuse to avoid the task.

Personally, I enjoy sanding because it transforms good woodwork into exceptional wood work.

Sanding is one of the simplest of all woodworking tools to learn to use.  Failure to use sandpaper is obvious in the work so if you are not willing to do it then you will be marked as a poor craftsman.  Sorry, but that's the truth.

My rule is to sand every single wood part in the project regardless of whether or not it's ever seen again.  I sand spars on all sides before they are glued in place, shear webs, formers, triangle stock everything.  It makes a noticeable difference.

Chant the following mantra to yourself until you become a true believer and sandpaper becomes not just a tool, but a lifestyle:

"Sandpaper is my friend.  Sandpaper is my friend.  Sandpaper is my friend..."

Also see

 
 

Sandpaper

Never carve when you can saw

Never sand when you can carve

Sanding actually takes very little time if you select the right paper and select the proper block for the job.  It is important to purchase good sandpaper.  As far as I am concerned, 3M Sandblaster paper is the best sandpaper available bar none.  Norton sandpaper is also excellent and generally a little bit less expensive than 3M.

I have been using Sandblaster paper for the past few years.  From the first time I used it I could tell the difference in how it cuts the wood.  That is what sandpaper does, by the way.  It is little pieces of grit adhered to a backing that cuts away material.

Sandpaper comes in a variety of types.  I do not consider sanding to be a chore.  Because most people do, selecting the correct sandpaper for any given task will lessen the pain they have to endure.

Apparently aluminum oxide will chip during use so that it stays sharp longer.

According to a now defunct Woodzone link, garnet paper does not have this property and so doesn't last as long.

Garnet paper will provide a better finish which I can confirm.  I have used both types of sandpaper and prefer garnet over aluminum oxide.

Wet or Dry sandpaper is designed for non-porous surfaces.  It is good for sanding paint, fiberglass, metal, etc.  Finer grades are good for finish-sanding balsa wood.

Garnet paper is made for wood and what you should buy.

Flint paper is for kids at summer camp and should never enter your shop.

Aluminum Oxide paper can be used for wood or metal.  See sidebar for more information.

Note that Garnet and Flint papers are not water proof.  In fact, I live in Florida and my shop is not climate controlled.  During periods of high humidity, my sandpaper absorbs enough moisture from the air that it wears out very quickly.

I buy boxes of the grades I use most often (220 and 360) in larger quantities and 5 packs of 80 and 150 grit because they tend to last longer when used on soft balsa wood.

I buy the assortments of Wet or Dry paper because they last a long time as well if I take care of them.  The pieces I use for wet sanding are rinsed thoroughly and then hung up to dry using clothes pins.  When I come across very fine Wet or Dry paper (finer than 1000 grit) I usually buy several pieces because it can be difficult to find.

There are polishing kits available for taking scratches out of clear plastic (motorcycle windscreens, for example) that come with very fine grades of sandpaper 12,000 grit amazingly enough.  It is cloth backed and good for taking imperfections from clear plastic parts usually canopies.  A 12" x 12" sheet of this paper is almost $15.00, but the kits contain a variety of grits in smaller sizes.  It is worth purchasing one of the kits if you want to have scratch-free canopies.

To accomplish your work faster and use less sandpaper it is important to learn when and why to use which grade.  A common mistake is starting out with too fine of a grade.  This is the main reason people think that sanding takes a long time.  If the first paper you use is 400 grit, then it will take forever to flatten a part or even get it close to being finished.

Generally speaking, coarse papers are used for rough shaping and flattening.  Medium papers are used for final shaping and removing scratches from coarse papers.

For bare wood that will be covered, fine paper is an acceptable stopping point.  However, even wood as soft as balsa can be polished.  This is where ultra fine papers come in.

Do not switch grits until the paper you are using has removed all the scratches from the previous paper.  For example, if you start with 100 grit and then move to 150 grit, do not switch to 180 grit until all the 100 grit scratches are gone.

If you move to a finer grade before completely removing the scratches of the previous grade, you will either do too much work to remove the scratches or have scratches left in the wood.

You do not need to move progressively through each grit in most cases.  Again, experience will be very helpful to you in knowing when to stop with one paper and what the next one should be.

When you begin using fine paper, you should be finished or very close to finished shaping the part.  At this point you are preparing it for the final finish.

 
 

Selecting Sandpaper based on the material

I discovered long ago that sandpaper manufacturers do not take balsa wood into account when they grade their papers in terms of fine, medium and coarse grit.  Some manufacturers do not even list the actual grit on the packaging or the paper itself.  I don't buy it if that's the case.

Also note that grades vary between manufacturers.  In other words, one manufacturer's 220 grit garnet paper may be significantly coarser or finer than another manufacturer's.

Sandpaper chart

This is more or less how I grade my sandpaper.  Your own experience will be more useful to you but this will give you a starting point if you are a beginner.

  • S indicates a good starting point for typical sanding.

    You may want to start with a different tool such as a wood plane or coarser paper if the material has very deep scratches, needs coarse shaping or has other serious imperfections.

  • F indicates a good stopping point so that you can proceed with the rest of the finish.

    You may want to continue with finer papers to put a shine on the material (wood included).

Ultra Coarse

 

Coarse

 

Medium

 

Fine

 

Ultra Fine

 

Grit

Material

60 80 100 120 150 180 220 320 400 600 800 1000 1600+
Hardwood/Birch Plywood       S         F        
Hard balsa/Lite Ply           S     F        
Medium Balsa             S     F      
Contest balsa               S     F    
Fiberglass, Plastics and metals                 S     F  
 
 

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