Method #2 for duplicating the white plastic parts
This method uses sheet plastic and a vacuum former.
- Sheet plastic
- Plaster of Paris (or similar plaster product)
- Rubber mold making materials (optional)
- Vacuum cleaner (a standard household vacuum cleaner is adequate)
- Heat source (electric burner, oven, etc)
- Vacuum former (build your own or buy one from Shorty's Basement - they are made by Chris Boehm)
- Heat resistant gloves
Hints and Tips
- Remove the dust bag/filter from your vacuum cleaner for a stronger vacuum source
- Make sure the plaster mold is as smooth as possible and free of dust or it will show up in the new part. Micro-Fill or just about any other filler/putty that dries hard will help fill holes. You can alter the plaster mold to fix errors in the original part or add details like rivits.
Vacuum Forming a New Part:
- Make sure the part is clean and is held level, then pour it full of plaster. It will be helpful to insert a dowel or thick balsa stick into the plaster to provide a handle for demolding. After about 1 hour carefully remove the plaster mold and set it aside for a day or three to fully dry.
- Shown below is the plaster mold removed after an hour. I did a poor job of pouring the plaster and managed to trap three air bubbles that will need to get filled. Fill in unwanted imperfections with you favorite filler/putty (I used Micro-Fill) and sand smooth.
- Cut a piece of sheet plastic the size of the holder (6" x 8" for my vacuum former). Shown below is a 10.25" plastic plate I purchased at a local grocery store, $3 for 15 plates. Chris Bohem found that plates like this average 0.016" in thickness, which is great for fliers (cosmetic parts) but not so good for cowls and other structural components. Plastic sheet can be purchased from Micro-Mark or your LHS, but they will cost about $1-3 per 6"x8" piece, depending on thickness and material type.
- Clamp the plastic sheet into the frame as shown below. I found out that these clamps need to be slid out to the edge or they will get in the way and the metal frame will not seal well against the vacuum former box.
- You can heat the plastic by holding it about 2" above an electric stove burner (or hot plate) or in a 350F (177C) oven. I chose to use a small toaster oven that I got from a local store for $30. Since plastic sags when hot you need to raise the holder. The picture below shows a drip pan that came with the toaster oven and four sockets being used as spacers.
- Set up the plaster mold on the vacuum former base as shown below. Plug your vacuum cleaner into the box and set it all up as close to your heat source as you can. Note that later on I raised the mold to 1/2" above the platen to avoid webbing.
- Preheat the oven to 350F (177C) then insert the plastic sheet. If using a burner then hold the plastic about 2" above the burner while wearing gloves. The plastic will start to wrinkle a bit then start to sag down. I waited till I had a little over 1/2" of sag before removing it from the oven. The picture below was a few seconds before the proper sag was reached, if you took it out at this point it would be too cold and not form properly.
- The next series of steps can be taken in any order you like, except that you must have the vacuum running before removing the plastic from heat so that you can immediately place the hot plastic onto the vacuum former. When the plastic is starting to sag I flip on the vacuum cleaner, then when the plastic has sagged sufficiently I remove the holder from the oven (while wearing gloves) and quickly set it down over the box, making a seal against it. Then I turn off the vacuum cleaner and the oven. Do you see those ridges or "webbing" in the plastic? This was not an issue on the canopy but plagued me on this part. It is essentially an effect of the plastic stretching in the oven then the excess having nowhere to go.
- If you take the plastic out too soon it will not form properly as seen below.
- Carefully trim the plastic part around the edge of the plaster mold and remove the mold from the plastic. Shown below, from left to right, are the original cowl, the vacuum formed cowl, and the plaster mold. The webbing on this cowl could be trimmed off and the gap that is left filled in, but let's try again to see if we can get rid of the webbing completely.
- One way to remove the webbing is to raise the mold up so that the webbing falls below the mold and does not effect it. On the cowl I needed 1/2" but the canopy only needed about 3/8". Another possible solution may be to just lie the part flat on the platen with no stand off, I will update this page if that works out for me.
- Trim the part to fit your plane and install.