I recently posted photos of the M-20 Diamond T prime mover and have begun to collect information on how to do the trailer. But the trailer would look pretty empty without a load of some kind. Originally designed for the Brits to move tanks to the English coast in case of attack from Europe, the M-20 also carried goods and equipment for the Allies following the Normandy invasion. Included were D-7 bulldozers. So the logical thing was to try and build one that resembled the D-7. AMT did the Cat D-8 years ago and I am fortunate enough to have a couple of them.
The AMT D-8 bulldozer kit is a great kit in many ways but the tracks that were included are absolutely horrible! First of all they are the wrong shape and have grousers that are too tall and thick. They are linked together by small pins that snap into holes in the bottom of the track plates. Real tracks do not do that.
So I decided to see if better looking tracks could be made. There are several photos on line as to how they actually look and a Tankograd booklet is on the way that will show a host of details and how they may differ from kit parts. After a couple of tries I came up with this. The kit track plates are a good width from side to side but a little wide edge to edge. I started by making a track plate from brass sheet and soldered the grouser to the plate.
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In the photo is one of the side frames of the AMT dozer with the kit tracks in front of it. In front of them are a set of links that will take their place. Beside the links is a brass master for the track plate and two links made of Evergreen strip stock. I added some pieces of hex rod for bolt heads to the brass master. In the left foreground is the initlal mold that was made using the brass master. It turned out ok but it left me with the task of making several duplicate links, each time gluing two pieces of strip stock together and then drilling out holes that were the correct spacing every time. Not only is this impractical, it is nearly impossible to do by hand.
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The photo above shows two sets of cast tracks. The portion on the right is an original try that was refined. Initially individual links were made of plastic and set in a jig for spacing. Then the track plate was glued to them. However, this meant that no two completed track pieces would be the same. The answer was to cast a track plate, add the links and then cast them as a unit. That is what the mold is to the right front. The problem there, however is to make sure that when the liquid resin is poured into the mold that it completely fills the voids and without any bubbles.
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The mold is now filled with casting resin, a little on each side before it is joined together. Quick work is the order of the day since the resin tends to set quickly.
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After a while the resin is cured white and hard. The mold is taken apart and this is what is first seen. The top of the track plate and some flash. Now comes the critical part and the hope that the resin filled the voids where the track links are.
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Well, this one for the most part is fine. However, there were some small voids in one end of the links that did not get cast. Fortunately they are small and can be fully formed by adding some putty to the ends and letting that set. A bit of filing and then opening up the holes will make it ready for connection to the track set.
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Here's the back of the track showing the links cast integrally with the track plate. With each one cast this way it insures that each one is an exact duplicate of the one before it. As you can see in the photos, they go together quite well. The connecting pins are sections of plastic rod. Now it's only going to take me several days to do a complete set!! HAH! I'm retired!!