When building gliders one item that is almost always used is sandpaper and the process of removing material using sandpaper is called sanding. Sanding is something that almost everybody has done but few have been given lessons or instructions on how to sand. The inexperienced builder sometimes consider sanding easy and not much to it, but the experienced model realizes that sanding is an art that takes practice and years of experience before done correctly. The typical instructions for building a glider just tells one to sand the balsa wood to shape. This document will explain my techniques for sanding/building gliders.
Sanding is the process of removing material by taking a rough/harder surface and moving it across the piece that you what material removed from. The rough/harder surface is typically referred to as sandpaper and small "stones" on the paper grooves/cuts out material.
For the construction of gliders sanding is typically used to shape the airfoil of the wing, elevator and rudder. These shapes need to be precisely made (to within a few thousands of an inch; .002") if you want a glider to perform well.
Sanding vs. Planing
Many builders plane or carve the wood before they start sanding it to shape, especially if there is a lot of wood to remove. The advantage of planning/carving wood is that it removes wood quickly and does not create a lot of dust. It also typically does not crush the wood as much as other techniques which remove/shape wood.
Hand plane is a typical tool which every glider builder has. See Photo 1. Hand planes are generally the combination of a cutting edge, such as a sharpened metal plate, attached to a firm body, that when moved over a wood surface, take up relatively uniform shavings, by nature of the body riding on the 'high spots' in the wood.
A Razor Hand Plane
The disadvantage I find with the planning/carving process is you have less control of the amount of material you are removing and you need to learn another woodworker’s technique.
I still have not mastered the art of planning wood so I do not use the planning process when building a glider. I just sand longer and make more dust.
Tools For Sanding
One must think of sandpaper as a replacement part for the tool that is called a sanding block. You typically should do very little sanding without a sanding block. Why? Well I believe you lose control if you sand with just sanding paper. Sanding without a hard flat backing surface is the easiest way to make waves in the part that you are trying to shape.
So the first tool you need is a sanding block, actually many sanding blocks. See Photo 2 for my collection of sanding blocks. Now you can go to the typically hardware store and purchase a sanding block, but I don’t and here why. First the store’s sanding blocks are heavy and I need/want control. I don’t need some heavy sanding block, pushing on the wood, making me fight the forces of gravity while I am sanding. Also, the sizes and shapes in the hardware store never seem to be right for me. So I build my own sanding blocks out of balsa wood. Now you don’t need to use your lightest wood, just some junk balsa blocks with do just fine. You can cut the block to any size and shape you want and make it fit you hand, because to have control you need to be comfortable. Later I will discuss how to make a flat portion on your sanding block. Other things to note about a sanding block. The sandpaper must be attached to the entire surface of the block. I use double sided tape to accomplish this. If the sandpaper is allowed to float off the flat surface, your sanding precision will decrease. Also make sanding block as large as possible. The larger the sanding block the harder it is to rock the block. On the other hand you do need some small sanding blocks to sand in tight places.
Collection of many different size and grit Balsa Sanding Blocks
The next tool you need is a hard, flat surface to sand on. I use glass plate. If you watch the garbage others throw out, you can typically find pieces of glass at the curb. The best is when someone replaces their wi