Here is a method of creating perfect fillets every time with very little sanding.
- Realize that you can only do two at a time.
- Place the airframe in a jig that will hold it horizontally without the fins touching. Hang the fins off the table top if necessary.
- Turn the airframe so that 2 fins are pointed up and the fin tips are level Should look like an upside down “V. The two fillets inside of the “V” are the ones that will be filleted.
- Put masking tape on each end of the fillet where epoxy could run off and down the side of the tube. Make a dam with it. Do this on all four corners of the fillets you are working on.
- Mix enough 15 minute epoxy to put about 1/4” thickness over both fillets and carefully pour it onto the fin/airframe joint surface and allow it to level out to both ends. Lift the airframe and tilt it forward and backward to accomodate the spreading of the epoxy.
- When the epoxy has settled evenly to both ends, rotate the airframe side to side to run it up on the fin and then airframe a good 1/4” to 3/8” above the joint. Rotate the other direction to complete the flowing out of the epoxy and then return it to the centered, leveled position where both fin tips are level.
- By this time, the epoxy should beginning to gel. Take your finger, dip it into a small container of rubbing alcohol and run it up and down the epoxy fillet to smooth it out. The alcohol will allow you to smooth the joint perfectly.
- Allow to dry sufficiently so as not to sag when rotated around for the other fillets.
- Once all fillets are done, allow to dry overnight and remove the masking tape dams. Sand smooth transitions into front and rear of fillets using a round file and then sandpaper.
The author has used this method to product perfect fillets for years.
Submitted by: Darrell Mobley