Rebuilding disintegrated deflection yoke covers

[ohohyodafarted]

As many of you are aware, many early color deflection yoke covers were made of a plastic that was prone to disintegrating over the years. The plastic used to make these covers is a molded thermoplastic that is made with nitorcellulose and camphor. It's called Celluloid. Here is a link to information about this old type of plastic which is not used much anymore.

http://plastics.inwiki.org/Celluloid

So the question is.... What can be done with the disintegrated celluloid deflection yoke covers. The answer is nothing... you must fabricate new parts from scratch.

This essay is a tutorial on how you can make replacements using easy to obtain user friendly materials.

The material I am using is model builders Styrene. I get it from Walthers model train supply but most hobby shops carry it too. It is made by Evergreen. I use .080" thick for the round discs, and .040" for the edge material.

Cuting the styrene is very easy. All you need is a utility knife to score the styrene. Then you place the score along the edge of a table and bend at the score. The styrene will snap where you score it.

Gluing, or more correctly "fusing" styrene is very easy and fast. Styrene will fuse with a liquid cement that sort of melts the styrene. All you have to do is hold the two pieces together and let the cement seep into the joint. In a couple minutes the joint will hold and in about an hour the joint will be very strong.

Here is how I rebuilt a delfection yoke for John Folsom's very rare 21" 1956 Motorlola that is in the process of being restored. Thumbnails 1 and 2 show the condition of the yoke as I received it.

The first step is to carefully disassemble the yoke so it can be worked on. In this case, both the back cover and the body of the yoke that the cover mates with, were totally shot. (thumbnail 3 is the disassembled yoke)

I started by building the body first.

First step is cutting a square peice of .080 thickness styrene about 1/2" larger than the diameter of the cover. I find the center of the square and drill a 3/8" hole. Then I mount the styrene in my lathe and turn the outside diameter to the correct size. (thumbnail 4 and 5) Then I reset my lathe tool and cut through the disc to make the correct diameter for the hole in the middle of the disc that will go around the body of the yoke. (thumbnail 6)

The disc is now ready for attachments of the edge pieces. The edge pieces are made of .040" thickness styrene. I cut 2 strips 1.125" wide by 21" long. I drag the strips of styrene over my thumb to creat a curvature in the plastic. (sort of like when you drag a ribon over the edge of a scissors to make it curl) Then I place the strip of styyrene around the circumference of the disc, and trim the strip to the correct length so the ends of the strip meet precisely.

Before attaching the edge strips, I took the disc and scored a line across the disc in the exact center so that LATER ON I can snap the disc into two equal semi-circles.

It is now time to attach the edge strip. Take a piece of scotch tape and join the ends of the edge piece together to form a circular ring. Place the ring around the circumference of the disc, making sure that the disc and the edge strip are flush to each other. Then apply the liquid cement and wait for the disc and edge strip to fuse together.

When the joint is solid (about 30 minutes) I took a tin snips and cut through the edge strip at the exact two points where the score I made previously on the disc, meets the edge piece. Then I snaped the disc into two halves. (thumbnail 7)

Edges of the parts are always made of two strips of .040" thick styrene bonded together in a fashion so as to stager the glue joints. So now I attach a second edge strip as shown in (thumbnail 8). AFter attaching the second edge strip to one half of the part, I installed the two semi-circular parts around the body of the yoke, and then I fused the edge strip to the second half of the part, thus joining the two halves of the body together into one solid piece. (thumbnail 9).

There are two terminal strips in this yoke. I used 5 minute epoxy and clamps to glue the terminal strips to the inside surface of the edge strip. (thumbnail 10)

The rear cover is fashioned in much the same way but it dosen't need to be cut in half like the body part was. The cover disc is made in the same fashion on the lathe, but it is about 3/16" larger in diameter and the center hole is smaller. The edge strips for the cover are also only 5/8" wide. Two edge strips are also used to make the edge of the cover, just as was done for the body part. Additional holes were drilled to accomodate aditional hardware that needed to be attached. (thumbnail 11 and 12)

Thumbnail 13 shows the completed deflection yoke with it's newly installed covers.

When attaching hardware such as screws or other fasteners, always use brass, aluminum or nylon fasterners. Never use any steel, or other fero-magnetic materials that will disturb the delicate magnetic fields that are createc by the deflection yoke.

Your deflection yoke may be different from this one, but the basic principals used on this project can be applied to almost any deflection yoke that has a disintegrated celluloid cover.

I hope this will be of help to some of you. Good luck!

Bob