Drilling cleanly through FG

What are some techniques to leave a clean hole on the back side in FG?
I've used forsner bit, regular drill bit, high speed, low speed, even trying CA on both sides, but still leaving fibers on the back side.

i put a piece of masking tape on the back side.

timbucktoo said:

i put a piece of masking tape on the back side.

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This works.

Or a piece of wood on the backside.

I've actually taken the time (for multiple holes) to tape a piece of sandpaper inside the rocket (grit side exposed) and sand a piece of pine to conform to the id. Secure and then drill from the outside. Remove it and place a drop of CA in the hole and ream again. Try not to force the drill (they dull quickly) so you don't delam the FG. Good holes for the most part. A drill press helps. If it's a bigger rocket and not in the recovery bay, you can re-use the block by trimming it down and using a threaded insert to retain a rail button, similar to what qquake has documented in his gazzilion build threads.

Sacrificial piece of coupler. Works perfect for a nice clean hole, every time.

Or section of airframe with slice out of it, so it will fit inside.

I also put a piece of masking tape on the outside surface and make my marks there. When the inevitable mismeasurement occurs, I can remove the tape and start over. The trick is to catch the error before drilling the hole.

All the time I thought the little fibers where by design, to keep the rivets, switches, shear pins in place....

I haven't done FG but for those splintery woods using a Brad point or Forsner with a big point in the center drill one side till the point just breaks through then flip it over, put the point in the small hole and drill from the other side. Works for fins and plates but obviously not for tubes.


Richard

blackjack2564 said:

Sacrificial piece of coupler.

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Aren't all airframe and coupler tubes sacrificial? But seriously, great timing for this thread - I have an order of fiberglass coming from Tim, and I beat up the last tubes pretty badly.

Jim