Polish and Repair

A bit of my workshop time was taken up by errands today. So my to do list didn’t get as much attention as I would have liked. Never the less, I took a few more bites of the proverbial elephant. It started with trimming the flanges.

The PVA came off with our mold, as expected. PVA basically creates a vinyl sheath around the part. PVA is, as our resident chemist Brian would say, is a polymer that is readily solubilized in water. For the rest of us, that means it washes off with soap and water. Even so, I find it entertaining, and slightly enjoyable to pull a big sheet of it off the part. I’m not going to lie, I spent an inordinate amount of time doing this, even though it would have been really quick to wash it off. Then I washed off whatever I didn’t get.

After that it was a simple matter of polishing and repair. For the polishing, I started with 1000 grit wet or dry paper on my 3 inch DA. I went over the surface paying a bit of extra time in certain areas. Anywhere where I could feel a surface abnormality, I sanded a little longer. There weren’t many of these areas. Most of them were areas where little pimples were present. These little pimples or nubs were from pin holes in the tool cowl. Even with 1000 grit, they went away quickly.

I was very happy with the 1000 grit surface, but as proud as I am of this part, I couldn’t stop there. I got the 1500 out and did the same thing with the 1500. It is amazing how smooth the mold surface feels. It is even more amazing how deft a hand is to feel little imperfections. Kinda fun.

Once the mold was polished I wanted to address some anomalies in the mold surface. Luckily, all of these spots were off the actual part and in flanges or excess areas that will be trimmed away. Even so, I wanted to fix these to ensure there isn’t any trouble pulling a part out of the mold and that there isn’t any excess epoxy curing there during a part run.

There were a few areas where there were voids. These are areas where the epoxy from the mold never made it down to the tool cowl/flange/fillet surface. There was one area where there was a large enough deformation of the clay fillet between the tool cowl and the flange to cause concern. In total, there were 7 places that required attention.

I got out my pneumatic pencil die grinder and scuffed up the surface in these areas to promote adhesion, but I left any ridges around these voids to retain the filler. I also put a piece of vinyl tape over each area to act as a mask. I then, using a very sharp new razor, cut out the profile of the void. It was then a simple matter of mixing up some micro to a wet, but stiff consistency and filling the anomalies. Once I was happy with the fill and surface of the fill, I remove the mask and had 7 nicely filled voids. A quick hit on each spot with 1000 then 1500 grit and the repairs were done.

The mold now needs to be waxed with 5 coats of PartAll No 2 mold release wax. That should be first thing tomorrow. Other than that, a quick spray of PVA and this mold will be ready to make its first part.

The first part I am going to pull from this mold will be a wet layup fiberglass part. I am going to call this Tool Cowl Serial Number 2 (TCSN2). There are a couple of reasons I am going to do this instead of going right to my final carbon fiber part.

  1. The fiberglass will be translucent, so I will be able to see through it for any potential conflicts and to ensure proper spacing from engine components.
  2. It is a cheap cowl that isn’t the final part so I won’t hesitate to cut, drill, sand, etc on this piece.
  3. It will allow me to make the plug for the lower cowl changes without worrying about damaging my top cowl.
  4. There may be changes to the top cowl like flanges, oil doors, etc that I will find as I progress along the way that can be incorporated into the mold.
  5. I can locate any mounting screws and features in the tool cowl with little repercussions to errors. Once these locations are accurately found, I can scribe them into the mold. These scribe marks will then transfer to the carbon part taking all the difficulty and guess work out.
  6. I can inexpensively try a layup schedule and new core materials to determine how I want to do the final part.

Tomorrow, I should get my carbon and fiberglass. If the day goes as planned, and my delivery arrives in a timely matter (it was supposed to be here today), I may be able to make TCSN2. Stay tuned.

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