My father and I didn’t start out using sanding shims when we created large intarsia projects for commercial installations. We would sand one piece, put it back in place and mark where it joined the next part. Then try to sand the next part down to the line as close as possible. It was years later we came up with the idea of sanding groups of pieces together as one unit. When I shape the pieces my goal is to make it look as real as possible. For example if I were sanding a horse with a white blaze, a color change on the coat does not mean the contour changes. After the parts are sanded they are removed from the sanding shim and I hand sand a very slight bevel around the edges of the parts.
The other time a sanding shim comes in handy is when you are blending in raised areas. Using the raccoon as an example, if I have two raising shims placed under the nose area to add more dimension I would need to blend the in the parts so it didn’t look like it had a stair step shaped nose. I use double-sided carpet tape to hold the parts onto the sanding shim, making sure the raising shims are taped in place before sanding.
I use an inexpensive “light duty” carpet tape. You will need at least two pieces of tape to hold each part down. I would rather turn the parts upside down to put the tape on the back of the parts rather than placing the tape on the sanding shim. This way I can make sure each part has enough tape to hold it down. Otherwise you practically have to cover the entire surface of the sanding shim with tape to ensure each part has tape. I really do not like to use that much tape, it makes it much harder to take the parts off the shim without breaking anything.
If there are more than one raising shim stacked up it is going to be easier to put the tape on each raising shim and the sanding shim. Then you have to carefully assemble the parts making sure the raising shims don’t interfere with the placement of the parts. The trick to this is not pressing anything down firmly until everything is in place.
The first piece of tape I put down I like to cover as many parts as possible to help keep the parts from shifting around. Instead of using lots of short pieces of tape I like to use long strips, it sure makes it easier to remove the paper from the tape. Sometimes it is a good idea to edge tape small parts that are on the perimeter of the section being sanded.
If you have trouble keeping the parts on your sanding shim there may be several reasons. One problem is the sanding shim is not flat or the parts were dusty and the tape did not make a good bond, or there isn’t enough tape to hold the part down, and last but not least perhaps you are pressing too hard against the sander.
We see many intarsia projects that have each part heavily rounded. It gives the project a quilted feel and accentuates each part that makes up the picture. There is nothing wrong with this, it is more of a personal sanding choice that each person decides how they want
their projects to look. As mentioned above I like to make it have the feel of the “real” subject I am making, so I have a realistic goal in mind. I think if each piece is heavily rounded the first thing you notice is all the different pieces of wood. Where as if they are sanded/contoured according to the real thing you see the completed piece and then you realize it is made up of many pieces of wood.
Another thought to keep in mind is balance. It can look redundant to have every part heavily rounded. To balance the project I like to have some mellow contours to help accentuate the more rounded parts. As an example the Mustang above has a mellow contour to the neck and the mane is much more rounded. Or the Big Foot Clown on the right, the fingers really stand out next to the flat soles of the shoes. The hair is more flat to help make the face look more dimensional. The face has a mellow contour to help make the nose stand out more. The same with the hat, it has a mellow contour, which makes the ball on top look much rounder than it is.