TWF Techniques: Sparless Wing Joiner Tube Installation (Part 3 of 4)
Posted by J.S. Decker on Dec 30, 2007, 15:03
11. Fit the joiner tubes. Test fit the joiner tubes in the cores using straight piece of 3/8-inch rod or brass tube in the joiner tube halves. Relieve the root rib holes as necessary to achieve the correct alignment. I use a Perma-Grit round rasp to enlarge the holes as necessary. You are ready to advance to the next step when you can easily and quickly push the joiner tubes through the root ribs, insert the 3/8-inch joiner, and accurately align the right and left side.
Test fitting the jointer tubes.
12. Tape the bottom of the joiner tube slot. Tape over the bottom of the slot with packing tape. Obtain a good seal around the perimeter of the slot.
13. Tape around the perimeter of the joiner tube slot. Tape around the perimeter of the joiner tube slot. Masking around the slot makes doctoring and cleaning up the "goo" easier. I typically use masking tape, but use clear tape whne the tape is applied over the reference line used to align the right and left wings.
Taping over the bottom of the slot (right) and taping around the top of the slot (left)
14. Mix the joiner goo. The goo is a mixture of laminating resin, 1/32-inch milled fiberglass, and microballoons. Mix the resin, stir in the milled fiberglass, and finally mix in enough microballoons that the mixture is pretty stiff and does not form a shiny surface when allowed to stand. I do this by feel, but I’ll give you some rough guess at the proportions. I mix up 20 grams of resin and hardener. I add about ½ to 1 teaspoon of milled fiberglass. I add several tablespoons of microballoons until I get the desired dryness/consistency that will glue everything together and sands reason able well. This amount of resin and the resulting goo will fill the annular volume of the right and left joiner tube slots.
Mixing the goo. I typically make about 20 grams of resin and hardener and add about twice this much 1/32-inch milled fiberglass.
Add microballoons until the mixture thick enough that the surface does not shinny.
15. Fill the joiner tube slot with goo. With cores held in the core beds, fill the joiner tube slot about half way with goo. Make sure that you work the goo into the corners and avoid creating air voids.
Fill the bottom of the slot with goo.
16. Insert the joiner tubes. Insert the joiner tubes, making sure that you put the plugged end in first and insert them angled toward the top surface as you insert them so that goo is not lift from the bottom of the slot. Once the joiner tube is inserted to the sub-rib and with the core held in the core bed, push the tube down into the goo until top of the tube is level with the sub-rib. DO NOT PUSH THE JOINER TUBE TOO DEEPLY INTO THE GOO. Doing so will require you lift the end of the up, which sucks the goo up and can create a void under the end of the tube that will have to be fixed later.
Insert the joiner tube. Angle the tube upward so that is does not push the goo off the bottom of the slot.
17. Set the alignment. With the cores held in the core beds, insert the straight joiner rod or piece of brass tubing. Align the right and left wings and the joiner tubes using weights to hold components in place as you proceed. Make sure the joiner tubes are pushed to the sub-rib and that the joiner tube is properly aligned horizontally and positioned vertically within the slot.
Insert the a joiner rod and set the alignment.
Final alignment check.
18. Crown the goo. Add more goo to fill the slot. Work goo around the joiner tube and crow the goo about 1/16 to 1/8 above the edge of the making tape. Check the alignment, you can check to see if the joiner tube is level by pushing something into the goo to check the depth of the joiner tube at each end and then carefully push a little additional goo into the void.