Tips for drilling medium (e.g. 1/4”) to larger size holes in G12 Fiberglass tube?

[jahall4]

A regular all-purpose drill bit like you use on metals (and sometimes wood) seems to work the best so far, but I’m not quite getting the results I would like to see. Every whole has at least a few strands that
“splinter” off the back side. I'm using a low RPM like you might use for metal.

 

[watermelonman]

Are you using an inner section as a drill block?

 

[jahall4]

Unfortunately these tubes would not have anything tight enough (say a matching coupler) to matter. Even if one used coupler for back blocking I suspect you would still get splintering right at the surface of the back side.

 

[JJSR]

I'd say don't push the bit, let it "feed"it self through per-say.

 

[blackjack2564]

Higher speed seems to work better for me.
Don't force bit...pushing down, forces splinter out the back.

Light touch works best, sandpaper wrapped around dowel to remove any fuzzies .
When I can use sacrificial coupler scrap for back-up, I get perfect holes.

 

[jahall4]

Higher speed seems to work better for me.
Don't force bit...pushing down, forces splinter out the back.

Light touch works best, sandpaper wrapped around dowel to remove any fuzzies .
When I can use sacrificial coupler scrap for back-up, I get perfect holes.

Do you typically use a standard twist bit? RPM?

 

[Bat-mite]

https://www.rocketryforum.com/showt...ean-holes-in-FW-FG-without-flaking-the-inside

 

[blackjack2564]

Do you typically use a standard twist bit? RPM?

Yes.....3000.

 

[jahall4]

Thanks for everyone's help on this including some great links to other threads. After some experimentation I have had what you might call perfect results using:

1) A high carbon steel brad point bit (1/4")
2) A back block of thick wall PVC pipe
3) RPM around 1400

You'll note a slot is cut out of the PVC pipe, which is slight larger that the G12 tube, so that it expands and effectively clamps itself to the tube.

Also note that nothing has been done to the tube in these pictures to that last hole, no sanding, no trimming the glass hairs, it is "as drilled"!

 

[Bat-mite]

The only difference between yours and mine is that I also put a strip of duct tape on the interior surface. Looks good. I still have a bunch of shear pin and rivet holes to drill.

 

[jahall4]

I do too. Everything is all jigged up and aligned on the press. I'll post some pics once I'm done.

I can see how the tape could be beneficial if your not sure the PVC is right up against the inside, but so far the FG has transitioned into the PVC in the hole with not discernible gap even when viewed with magnification.

 

[ChrisAttebery]

I back each hole with masking tape and a wood block. Then I drill a 1/8" pilot hole at each location. Finally, I use a Unibit to open the holes to the correct size. I usually sand the back side of the holes with 220 grit when I'm done to clean up any burrs.

 

[Flyfalcons]

Unibits are great. I use a sharpie to completely blacken the step of the diameter I want to drill to, this makes it easy to right step when drilling.