The following article provides instructions on how to carry out Propeller Leading edge repairs.
|It’s easy for your epoxy leading edge to get some chips and nicks. Here’s how to fix them.
|First clean the area that you are going to repair with rubbing alcohol. For this repair, we’re going to be using an epoxy called HPR-25. This epoxy is made by Adhesive Technologies in Auckland, New Zealand. It’s a fairly thick epoxy, so you don’t have to worry about it dripping off the prop while it’s waiting to dry.
Apply just enough epoxy to leave a bump that you can trim off the next day.
| If the epoxy is not yet rock hard when you come back the next day, you may be able to remove the excess epoxy with a utility knife, by carefully along the leading edge. Now sand the prop to its final contour, starting with 240 grit sandpaper and working up to 1200 or 1500 grit sandpaper.
Next polish the prop by hand with a rubbing compound that you can buy from an auto supply store. Clean your prop up and you’re done. If you used the same type of epoxy that was used to originally make the leading edge (and if you did things right) the repair will become invisible.
Here’s a second way to repair a damaged leading edge. For this repair we’re going to cut out the damaged area of wood and replace it with toughened epoxy. This is very similar to how you would put toughened epoxy on the leading edge of a new prop.
|Take your woodworker’s marking gauge, hold it as shown on the leading edge of the prop and scribe a line the length of your repair.
Make sure that you gently curve your cut into the proper depth at the beginning of the cut, and curve out of the proper depth at the end of the cut.
|When you are finished with the cut, your prop should look something like this. Be careful with your fingers. Now, sand the surface you just cut away to remove the saw marks.
|Apply masking tape on one side of the prop right next to the place where you just cut off the wood. This will protect the wood from the epoxy in the next step. Apply a wider strip of masking tape on the other side of the prop to make a masking tape “shelf” that the epoxy will rest on. This shelf or dam will help support the epoxy while it’s curing.
|It’s a good idea to trim the edge of the masking tape dam smooth with a pair of scissors before you apply the epoxy. This will make it a lot easier to get a good bead on the leading edge of the prop.
When you come back the next day, peel the tape off carefully. If you are skilled with a grinder you can grind off the leading edge carefully. If you aren’t skilled with a grinder start with 60 grit sandpaper on a urethane foam sanding block and sand the prop to the right shape. Work up to 120 grit. Use your marking gauge to make sure you’re leaving on the same amount of epoxy as you removed as wood.
|Even though you were being careful when you put that epoxy on the leading edge, you will probably end up with some pinholes in your epoxy. Now is the time to find them and fix them. Get a sharp steel object like a pin and look carefully at the leading edge for possible pinholes. They will show up as white spots. If you see a white spot, poke at it with the pin. If it comes out, it was a pinhole that needs to be filled.
|After you have your pinholes all opened up, blast off the leading edge with compressed air (remember your safety glasses). Next, put masking tape on the wood next to the epoxy leading edge to protect it during the pinhole filling process. Do this on both sides of the prop.
|Press hard with a putty knife to get the epoxy into all the pinholes. Then wipe the epoxy smoothly into the leading edge with a thin piece of plastic as shown.
|Put the prop aside and let it dry for yet one more day. When you come back, do lots more of that sanding and smoothing, sanding and smoothing, and pretty soon you’ll be ready to paint.
|Here’s the prop tip of the day. When you are moving your prop around your shop, set it on your foot instead of on the floor. You’re less likely to break it.
For more details on prop making and repair read, “How to Design, Build and Repair a Wooden Aircraft Propeller.