ndows, just pick up the window frame with the glass inside. It is pretty easy to remove the frame and then you will have your nice building surface. Marble is also good to work off of but more expensive and harder to find. See Photo Below.
Building/Sanding Surface. Note the duct tape at the one edge which is a sanding fixture/jig used to set the height (.025") of the trailing edge of a wing.
Another item I use a lot is masking/duct tape. It is amazing to me but sandpaper does not cut or sand duct tape or masking tape very well. So I use these tapes as tools and fixtures to control my sanding. I will discuss this a little more in detail later.
So to summarize, the tools you need are:
- Sanding Blocks: Lots of them!
- Sandpaper: Lots of different grits.
- A Flat Surface
- Double Sided Tape
- Masking\Duct Tape
I purchase all my sandpaper from the local hardware store. I found the cheaper sandpapers don’t do as good of job as the expensive ones. I use a 3M product called SandBlaster. See photo below.
SandBlaster sandpaper in a variety of grits.
Basically sandpaper is made from three components. One is the paper or backing surface the "stones" are glued on to. The cheaper sandpaper uses poor quality backing paper, which can be inconsistent in thickness and not very durable. Next is the glue which is used to glue the "stones" to the paper. Again the cheaper the sandpaper the poorer the quality of glue is used. Finally there are the "stones". There are two important features of the stones. One is what material they are made from. Stones made from hard material make sanding process easier and more precise. The second is the size of the "stones". The size of the stone is characterized by the grit of the sandpaper. Sandpaper comes in a variety of grits usually ranging for 60 to 1500. 60 grit is very rough and 1500 grit is very smooth. . A table below shows the sandpaper grit number and the corresponding "stone" size.
|Grit||Average Particle Size (in)|
Precision And Grit Number
If one spends some time to think about things is pretty clear the lower the grit number the more material is removed per each stroke. Also the more material that is remove the less precision you will have. If one puts a piece of sandpaper under a microscope they would see the following;
Also if one puts the piece that is being sanding under the microscope they will also see similar mountains and valleys.
If one want to shape something precise then these mountains and valleys needs to be minimized. In engineering terms this is referred to as surface finish. If someone wants to make a wing .235" thick at the high point and wants the thickness to be precise to .001" then it should be clear one needs to be sanding with at least a 320 grit sandpaper (see table above).
Going Through The Grits
Woodworkers have used the term "going through the grits" to describe how one should properly sand. What this means is that you should start with low number grit sandpaper and as you get closer to the desired shape or thickness you start going up in grit number. Here’s my general rule of thumb;
|Grit||Distance From Desired Shape|
At the low grit numbers I find that the stones tear the wood and one needs to be careful not to tear the balsa wood which creates large valleys.
Making A Sanding Block
Making a sanding block is easy once you know how. Get a piece of balsa wood and cut it into a block. Shape the top and sides of the block to make it feel good in your hand. Next make the flat sanding portion of the block by using your flat sanding surface. Typically you want a very flat, smooth surface on the sanding block which you attach the sandpaper to. To get your sanding block flat and smooth, I use sandpaper, a aluminum plate and some double sided tape. Attach a large 8.5"X11" piece of sandpaper to the aluminum plate using the double sided tape and then just take your sanding block and sand the surface flat. See Photo 5. Be careful not to rock the sanding block as you move it across the sandpaper.
Flat Aluminum Surface with Sandpaper attached to make sanding blocks.
A roll of dou