Today I am going to be working on the Intake manifold, it can be seen below in green and indicated by the arrow. I am going to be attempting Terry’s Epoxy Encapsulation Technique (TEET) as the part is machined from two sides and work holding would be very tricky otherwise.
I design the part, then the encapsulation fixture. I go to the mill, square up a block of aluminum, then measure it and put the exact dimension back in my model. There is a runner that needs to be drilled all the way through to create the internal fuel/air passage from the carburetor to the cylinder head. Then aluminum plugs are turned on the lathe for a snug fit and pushed into position just the right depth.
The drawing below has all the dimensions I need to fabricate the initial fixture/work piece including the through hole and the aluminum end plugs for the lengthwise fuel/air passage. Note that I have also drilled two 5/16″ end mill entry holes into the work piece. My little CNC router complains when I drive an end mill straight down into the work piece, but if I provide the entry hole then only side mill, I can run at higher speeds without stressing the setup.
The tool paths are created and simulated. I use an adaptive clearing strategy to remove most of the material, a ramp strategy to mill the vertical sides, a horizontal strategy to mill the flat horizontal surfaces; these all use a 1/4″ end mill. A 1/8″ ball end mill is then used to create all of the internal and external fillets.
Below is the work piece after machining the top.
I then use 5 minute epoxy to encapsulate the intake manifold. The amount of epoxy used was great enough that the exothermic rection of the mixed epoxy cured very rapidly and I did not need to wait long to move on to machining the back. I then repeat the tool path generation and machining of the back side. When I touch off on the back side I am careful to use the same datum points as I did for the top as it is very important that the two machining operations meet as accurately as possible so the features are not noticeably offset.
Below is the back side of the work piece after machining. I am pleased with the alignment of the top and bottom machining operations.
I then heated the part for 1 hour at 275 degrees as Terry did. The 5 minute epoxy I used did not decompose, but just got soft. I was able to remove the intake manifold from the fixture, but as the part cooled the epoxy just got rock hard again. I think I just post cured it. I had to reheat and then work quickly with a rag to remove as much of the softened epoxy as I could. I used “Quick Set” epoxy from Ace Hardware instead of the Devcon 5 minute epoxy Terry used. Most of the epoxy reside was removed as I did my final filing and hand finishing of the part, and the sand blaster got the last of it. I did not want to use a higher temperature as I used Loctite 638 to secure the end plugs, which is a high strength, high temp adhesive, but it too will get soft at higher temperatures.
All for now, thanks.