What size hole for an epoxy "plug" ?

[TimC2520]

I am going to be mounting a radar pedestal in the coming weeks on the pilot house roof of a 2520. The four bolts are 3/8". Also, best style bit for the drilling?
Thanks.

Also, do you think this could be done in one day? I only get down once a week so this could be a "2 week project" to install 4 bolts.

 

[warthog5]

Doing it right will require time.

It's a balsa cored top. The LAST thing you want is water intrusion into Balsa Core.

I mock it up..... Drill the holes 1/2in. Now take a allen wrench.... Grind the short side to a point. You want one that will fit in the 1/2in hole [short side of wrench.

Chuck the wrench [long side] in a drill motor. Your going to use this to carve out more Balsa core past the edge of the 1/2in hole.

Once that all done.... Tape the inside and fill the hole with epoxy /Cabisol mix. Don't make it to thick. You want the air bubbles to escape before the epoxy kicks off.

Usually the epoxy settles and the hole needs to be topped off again with epoxy /cabisol the next day.

Once it's all cured.... Redirll the holes to 7/16...... 1/16 larger than the bolts. Use 3M 4000UV to seal the bolts and the edge of the mounting flange.

I suggest you drill the holes.... Mock it all up dry.... Tape the top carefully 1/16in back from the flange. Now add the sealent.

When the squeeze out happens run your finger around the flange and this creates a neat little fillet of sealer around the flange. Now pull the tape.



You asked how to do it right. This is how you do it. This is NOT the way a production shop would do it. But this is the way you do it and NEVER have a problem down the road.

A production shop doesn't care if your coring is rotted 5yrs down the road.

 

[bean]

Warthog,
I love the details in your posts it is great to see someone that noes what they are doing. Keep it up.

" Bean "

 

[Brent]

Thanks

 

[TimC2520]

Thanks, how about the bit? Will a spade bit do the trick?

 

[warthog5]

Thank You Bean.....It's part of my OCD .



The bit itself is not real important, in the size holes we are talking here. Brad point will work well.


I use a set of layout punches a lot. The give you an exact center when doing your layout.

These are layout punches or Transfer punches. Harbor Freight has them. This set has all the sizes the same as a good drill bit set ..... up to 1/2in

 

[sailmaster]

Have you tried casting a nut into your cored deck?
Same system but do not drill through panel Undercut and fill with epoxy
Set WAXED bolts into wet epoxy and they can be removed
Gougeon talks about this in their book