Engine Cowl Part 6 (Final Plaster Work)

I had hoped to be farther along at this point in the project, we have had some bad weather down here that has caused a bit of a disruption in the build. Either a tornado or straight line winds of 95 mph hit our area and damaged some of my fencing. I had to use some of my free time to straighten and fix this. Then I was sent on another trip to Charleston and thats actually where I am at right now. Before I left last Monday I was able to complete both the upper and lower final splashes. I am using the plaster splash method of making the final mold masters for my cowling. This process is needed because of the desire to build a lower cowl that joggles under the upper cowl. This means that the lower cowl OML (Outside Mold Line) will transition to a negative .080 offset from the master OML surface. In order to do this a female plaster splash of the foam master had to be completed. This is where I left off on part 5. The foam master had the actual trim lines scribed into it so the location of the joggled flange could be determined.

Upper cowl splash

The first splash taken from the female was for the upper cowl. By reversing these molds, low spots become high spots and pin holes become "pimples" That means that the surface quality actually keeps improving as I get closer to the final lay up tool.

This is the upper splash. The next step will be to make the upper cowl lay up mold.


The main reason for doing all of this additional work was to make lay up mold with the flange joggled. Here is a picture of the female splash with the pattern wax laid in to simulate the joggled area.

Female Splash with pattern wax


This is a standard product called pattern wax. It comes in various thicknesses. This particular thickness is .080" I cut two inch wide strips of this wax and set them in such that they extended upward past the lower cowl trim line.









another view of pattern wax

 
This is another view of the pattern wax showing it as it transitions thru the L/H inlet area. Pattern wax can be bought with an adhesive backing or bare. The adhesive has about the same "Tackiness" as a Post it Note, so I sprayed some 3M 777 adhesive in addition to the supplied adhesive.

The pink area on the female splash is a repaired area using bondo.



Lower Splash mounted on MDH Board


This is the lower cowl mounted on a piece of MDH board and ready for the lay up of the actual mold. The splash was mounted with  plaster and an extension was added with plaster to the flange to ensure enough excess tool margin. The raw plaster will be coated with a mixture of Shellac thinned with alcohol . 5 coats of Carnuba mold wax will be applied and then a coat of PVA water soluable release coat.

I will update this blog when I return from Charleston in early June.