Hole Drilling

Hello,
I was wondering if anyone knew of a way to drill holes in a body tube given pre-drilled holes in a coupler. It is a 4 inch LOC tubing avionics bay, and I need to drill holes in the body tube to align with the screw holes. I would prefer not to have to drill new ones given that these already have t-nuts in there...

Thanks!


Matt

You might be able to poke a pin through from the inside to make a mark for drilling from the outside.

Try sitting in a darkened room with a small but high-lumen flashlight and a pencil. Put the flashlight in the airframe and place aluminum foil (shiny side in) on the ends and either tape or secure with rubber bands. See if you can detect light from the coupler holes and mark with a pencil.

Greg

Slip the tubes back to expose the holes in the coupler. Mark the location of the holes on the BT and use your angle to make lines along the BT (like you are marking for fin locations). Go back and measure the distance from where the end of the BT will be (switch band edge?), down to the hole and transfer that to your line on the BT. Your lines and measurements must be true for this to work. I am 1 for 1 using this method on 1.9" tube, YMMV

Test the hole in the coupler with various drill bits until you find the one that fits through the T nut. Tape the coupler into the mounting tube with the bulkhead remove. Put the drill bit that fits into the T nut and using your thumb and forefinger twirl the bit back and forth with light pressure, slowly drilling back through the airframe. When you start to see the bit push up on the cardboard tube, stop and tape a small block of balsawood covering the dimple in the airframe. Once in place, go back and resume the bit twirling. It's seems slow but it really isn't. Should be able to drill through in a couple of minutes.

I'll add another method: place BT on coupler to correct depth, draw line around bottom of BT to coupler. Measure up to the center of hole in coupler from that line. now transfer that measurement to the position on BT you want your first hole. This first hole depends on what else might be inline with your holes or the way you want your BT positioned. If it doesn't matter where the holes are the first hole can be anywhere on the BT at the correct height. Drill hole in BT. Now make a ring of typing paper, what ever and tape around BT tight enough just to be able to slide it on the BT. Your fist hole in the BT should be in position lined up with hole in coupler. Mark the center of that hole at bottom of paper ring. Slide ring to bottom of BT and line up with that SAME hole on coupler,(slide bottom of BT to holes on coupler) secure ring with tape??? keep from moving!!

Now mark the center of your other holes in the coupler to the paper ring. Slide ring back to line up with first drilled hole.(center) Transfer lines to BT. I don't know if your holes in the coupler are all at the same distance from the bottom of the coupler or not. If they are you can center that paper ring height wise in the center of your first hole and mark the bottom of your paper ring, that will give you exact centers to drill your holes. If they are not the same height measure up from the line around the coupler you made earlier to each hole and mark accordingly on the BT. GOOD LUCK !! Try the light idea first.

Matt- believe it or not, but we used a stiff wire bent in half with small 90 deg bends facing (and touching) each other at the ends on the DC10 for repairs. Position your couplers/whatever and locate the inside hole with one end of the bent wire. The 'outside' end of the wire is a good approximation of your hole location. Use a #80 drill and then pull the hole in whatever direction you need to be centered. I used music wire for locating a very strange av bay in my 6" scratcher "AfricanIzed" but a wire coat hanger could be adapted.