1/4-Scale 5 HP Red Wing: Part 2

| December/January 2004

Engine frame and jig attached to the lathe

Photo 1: Engine frame and jig attached to the lathe in preparation for boring.

Editor's note: This is part two of a four-part series. Read Part 1 

Last month I told you about how I became interested in model engines. We also went over a few milling steps that let us get started. This month I want to mill the engine frame as well as bore the cylinder. I think there will even be time to work with the flywheels, so let's get started.

Before the engine frame can be milled any further, it has to be attached to a jig. Some of the milling steps require that the engine frame be held sideways or at an angle. Because of the irregular shape of the engine frame, it would be very difficult to do without some type of jig.

Fabricating a jig
The jig I made is simply a flat piece of 3/8-inch steel that has been milled square on three sides. I made it about 12 inches long and 7 inches wide so there would be plenty of room for the jaws of the vise to grab. By having the three sides milled square, I just have to let the jig touch the bottom of the vise and it will square itself with the table.

With the engine frame attached to the jig, I decided to bore the cylinder. It is important to bore the cylinder before some of the other machining on the engine frame can proceed. This is because the cen-terline of the bore is used as a reference for some of the other steps.

I started by attaching the jig and engine frame to the lathe table. As you can see, I had to use several V-blocks and plates to center the bore with the center of the lathe.