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  #1  
Old 06-07-2021, 08:52 AM
RV10Pilot RV10Pilot is offline
 
Join Date: Jan 2005
Location: Medford, NJ USA
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Default Repairing Poorly Countersunk Holes in Fiberglass

One would have thought that by the time I got to attaching the empennage fairing I would have known how to countersink. Not. I am using tinnerman washers to hold the fairing in place, but I know I can do better.Not. The nut plates are attached. How do you recommend I fill the poorly countersunk holes and start over.
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  #2  
Old 06-07-2021, 09:04 AM
Ron B. Ron B. is offline
 
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If your not concerned about the rough hole (washer will hide ) then you can smooth out the counter sunk hole so that the washer sits better by having a piece of wood behind the glass clamped tight with the proper size hole for the center tip of your counter sink. This will stop the wandering of your counter sink.
If you want to repair the hole outside the counter sunk area you should grind a taper in your glass and glass over the hole and start over. I would try to glass from both sides, a little on each rather than all on one. Makes a stronger bond.
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  #3  
Old 06-07-2021, 09:38 AM
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wirejock wirejock is offline
 
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Default Countersink fiberglass

Once fixed try a dremel and stone to countersink.
Run the dremel on a sharpening stine to shape the point to the correct angle.
Make a nice countersink. I usually stop shallow and use a hand deburring tool with a countersink bit to finish.
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  #4  
Old 06-07-2021, 10:44 AM
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DanH DanH is offline
 
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slap some tape on the backside, wipe wet flox mix into the depression. cure, sand flush if needed, re-drill, countersink again.

Or just stop countersinking fiberglass. AN526's with nylon washers is the long term bulletproof solution.
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  #5  
Old 06-07-2021, 12:59 PM
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bjdecker bjdecker is offline
 
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Bond in some Tinnerman washers.
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  #6  
Old 06-07-2021, 05:58 PM
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To fill the holes, tape one side of the holes and the fill the hole flush with epoxy. Mix the epoxy thin enough so that it will flow into any minor cracks. Then re-drill in any manner you want. Your local marine supply store will have the epoxy you need, unless you just want to order online. Carefully dremel out the loose pieces of fiberglass on the edge of the holes before you fill.
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  #7  
Old 06-08-2021, 07:58 AM
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goatflieg goatflieg is offline
 
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Lancair sells abrasive countersink bits that are made for countersinking fiberglass. Worth the investment.
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  #8  
Old 06-08-2021, 08:26 AM
YvesCH YvesCH is offline
 
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You can use Perma Grit Tools:
https://www.permagrit.com/kt2/

Cheers Yves
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  #9  
Old 06-08-2021, 09:37 AM
John Tierney John Tierney is offline
 
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I have used this one with success, just very slow rotation:
https://www.permagrit.com/large-coun...ree-no-nipple/
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  #10  
Old 06-08-2021, 09:42 AM
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Dan 57 Dan 57 is online now
 
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Yep, did the same as Brian, bonded the fairing washers in. Better looks and durable if properly done.
In your case RV10Pilot, it looks like the cloth wasn’t properly saturated with resin in the first place...
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