Sketchup is an easy-to-learn program for 3D modeling. While it gives you an easy way to design creatively, it is a bit more challening to design accurately. If you are going to make physical models of your designs, you will need to make them small enough to fit on the tool that will make the part. You can send the 3D models to a number of toos, including the ShopBot, Mill and MakerBot, among others.

Here is a set of screenshots and a sample file that show the steps of this process.

Here are some steps to get you working accurately.

Open up Sketchup.

The default template is probably Architectural/inches.

This will give you a massive file. It is easier to work with a smaller file.

Change the snap settings by going to the Window menu and choosing Preferences.

Choose Template, and then Inches (Woodworking)-3D

To use the template, open a new file, and it will be using the woodworking inches template.

Instead of the person, you'll see an image of a carpenter's square. The increments on the square are one inch, you can test this by measuring with the tape measure tool.

Use the Tape Measure tool to make two guides at 2" from the red and green axes.

Choose the tape measure tool.

Click on the green axis and pull to the right. If you the line turns red, then you are parallel to the Red axis.

Type 2 on the keyboard. This will set the distance to 2 inches.

Click on the red axis and pull up. If the line turns green, then you are parallel to the green axis.

Type 2 on the keyboard. This will set the distance to 2 inches.

You now have guides for a 2 inch by 2 inch square.

Make the square

Use the rectangle tool.

Click at the origin, and drag to the opposite corner.

The tool should snap to the intersection of the two guides.

You can check to see if your shape is 2 inches square with the tape measure tool.

If it is not square, you can move your guides or replace them with new, more accurately positioned guides.

Extrude the square up.

Using the Push/Pull tool, push up the square.

Type 1.25 to set the height to 1 1/4 inches.

You now have a 3 dimensional shape that is 2 inches by 2 inches and 1 1/4 tall.