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How to drill clean holes in FW FG without flaking the inside?

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Bat-mite

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I just drilled two half-inch holes in the switchband of my Formula 200. I used a forstner bit. It had to get through about 1/4" of FG and the epoxy between the two layers.

The inside of the coupler flaked. I don't know if that's the right term.

Anyway, for my static ports (I'm going with four 3/8" holes), I need them to be clean and not flake. I will be buying a new bit for this. So:
  • Should I still be using a forstner bit?
  • Will a brand new one do better (cut cleaner)?
  • Should I put a layer of duct tape on the inside of the coupler?
  • Any other ideas to prevent flaking?
Thanks.
 

rharshberger

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A Brad Point bit would be a better choice along with a piece of wood against the back of the hole. Using a drill press will help as well as you can control the bits feed rate and pressure easier. Brad point bits have two longer spurs on the outer edge that will cut through the FG before the actual cutting edge hits the material, forstners are great for drilling flat bottomed holes.
 

Bat-mite

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Thanks for the suggestions, guys. If I use a wood block, it will obviously need to be at least slightly rounded. Any ideas on that? I'm trying to think if I happen to have a rounded piece of wood lying around the garage that I wouldn't mind drilling into.
 

rharshberger

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Thanks for the suggestions, guys. If I use a wood block, it will obviously need to be at least slightly rounded. Any ideas on that? I'm trying to think if I happen to have a rounded piece of wood lying around the garage that I wouldn't mind drilling into.
A piece of pine/hemlock (a piece of 2x4 works great) is fine and you can round it on a belt sander if you have one. I usually draw the profile of the tube on the end of the wood block and round it to match.
 

Worsaer

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Thanks for the suggestions, guys. If I use a wood block, it will obviously need to be at least slightly rounded. Any ideas on that? I'm trying to think if I happen to have a rounded piece of wood lying around the garage that I wouldn't mind drilling into.
I use an oak closet pole that I picked up at home depot. I place a clamp on both ends to ensure good pressure, and as already mentioned, drill holes with high quality brad point bits. Works great.
 

CzTeacherMan

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I use a fat dowel rod or spare chunks of wood. I never throw anything out, though, so I've always got a stockpile of scraps. Even with that, I'll still get a few fibers that "flake"... Just use a little sandpaper on a dowel rod to sand them off. That's as clean as it gets. If you have a big enough tube, try taping the inside where you'll drill. Basically, the point of the wood and/or tape is to hold the filaments against the drill bit so they're cut before the drill bit pushes them down/out. So a sharper bit moving faster will help also. Combine as many tips as you can to get the best cut you can get.
 

Bat-mite

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I use an oak closet pole that I picked up at home depot. I place a clamp on both ends to ensure good pressure, and as already mentioned, drill holes with high quality brad point bits. Works great.
Sounds like a winner! I'll let you know how it goes.
 

Bat-mite

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Okay, going to try this tonight. I'm using a 2" x 2' piece of PVC and brad point bits. Unfortunately, the only ones Home Depot had were rated for wood. No carbides or HSS. I think I'll put a strip of duct tape between the PVC and the coupler, too. Wish me luck.
 

CzTeacherMan

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Okay, going to try this tonight. I'm using a 2" x 2' piece of PVC and brad point bits. Unfortunately, the only ones Home Depot had were rated for wood. No carbides or HSS. I think I'll put a strip of duct tape between the PVC and the coupler, too. Wish me luck.
Good luck
 

AlphaHybrids

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I drill the hole I need 1/16" smaller. Then I apply some super glue around the edges. I then have a tapered reamer that I run through the hole to open it up. Then I follow through with a spiral fluted straight reamer.

Edward
 

Pat_B

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Put a piece of wax paper inside the airframe (or use mold release) and pour resin onto the surface. The resin will harden within 15 minutes and will have taken on the form of your airframe and will have a flat surface due to it being self leveling. You can keep the resin in place by using modeling clay around the perimeter of your intended form.
 

Bat-mite

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The duct tape/PVC/brad point bit method worked perfectly. I now have four excellent static ports in my switch band. I will use this method for rivets and shear pins, also. Thanks, everyone.
 

djkingsley

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I measure the tube I am going to drill and print a tube that is a couple tenths of a mm smaller diameter and slide in into the tube.

DrillBacking.jpg
 

mkadams001

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I know that you had success with the brad point bit but there are other options. You could use a bit designed specifically for acrylic and polycarbonate. It should work with fiberglass. The other would be a Unibit.
 
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