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Scratch Building - OMG, extrusion madness


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In my tutorial on scratch building distributors, I mentioned the concept of extrusions. Real extrusions are forced through a die to create the necessary shape. The parts I am making only mimic this effect, but their usefulness is the same. To me, this concept was the most important part of the tutorial.

Here's another example to show how handy this technique can be.

Once again, I'm starting with some round and 1/2 round styrene. In this instance, the core shape, at .080" is slightly smaller than the rod used for the distributor.


This rod was too small to fit in my aluminum heat sink, so I used a triangular file to cut a shallow groove in a small wooden block. The round rod was laid in this groove with a piece of masking tape holding it in place. The half round is then positioned along the top of the larger rod and also taped into place. Liquid cement is then applied to bond the two parts together.


It's important that the pieces of 1/2 round are directly opposite each other. To ensure this, the dot on the end of the 1/2 round will make it easier to check the orientation of the parts during construction. Once the glue sets up, this part is turned 90°. The mark on the end aids in making sure the rod is positioned correctly. Place another strip of 1/2 round opposite the first and glue it in place.


That's about it. How easy was that?

Give this assembly 24 hours to allow the glue to thoroughly dry and then it's ready to slice. The next post will show a few of the uses I've found for this particular shape.

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Here's some examples of how the newly "extruded" shape can be used.

This is a close-up of a Pontiac 421 with a scratch built intake. A thick section of the extrusion was sliced off the rod we just completed. I used a small round file to shape the bottom side so it would fit like a saddle over the coolant cross-over pipe. After the part was glued in place, the large center hole and two smaller holes were drilled. The center hole will help hold the radiator hose in place.


Here's another slice used for a radiator cap. The only addition needed was the pressure release button in the center. Imagine trying to create this part by creating a small disk and then attempting to create the small ears and glue them in place. This is much easier with the extrusion technique.


Finally, here's some slices of the extrusion used on some scratch built headers.I drilled a center hole into the end of the extrusion rod prior to cutting the discs. The holes were then reamed out to the size necessary to slip over the head tubes.


Now you've seen two different "extruded" shapes used to make scratch built parts. You may very likely think of some additional shapes to create with this process. Please share them when you do.

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Thanks for the support, John. I hope this technique will help you create some really groovy parts.

I like to get my money's worth out of these extrusions. The first example of a radiator cap was a bit out of focus. Here's a better one, although I should have used the smaller rod to make it more to scale. Why make make a radiator cap when most kits either come with one, or have it molded into the radiator? In my case, they are easy to lose. I also find that with a separate cap, it's easier to do a good job of painting the cap with a clear and sharp line between the silver and black. Plus it's fun to see what you can make.


Edited by Alyn
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