What size of drill for a hole in epoxy/balsa core deck fitting repair

F

FairweatherDave

Well-Known Member
Joined
28 Sep 2009
Messages
2,089
Location
Solent
Visit site
image: http://i77.photobucket.com/albums/j62/vyvcox/Yacht tech/Deckfittings.jpg

Read more at http://www.ybw.com/forums/showthrea...gs-through-the-deck/page2#IXUKLW3hgZodX2Xv.99

Apologies for the clumsy start above, please click on the link to see what I am doing. I have been following this method to the letter and have got to the stage of drilling the epoxy repairs, prior to refitting the deck fittings. The method says to drill a hole one drill size SMALLER than the bolt. (image 5). I just wanted to double check that here. I presume the idea is that my new bolts will cut their way through the epoxy reasonably easily and the end result will be a mega tight fit and a threaded hole? As usual the forum's advice much appreciated.
PS I will obviously be using sikaflex/ similar when actually doing the fitting. It is the drill size I am interested in here.
 
I have alwqays found it easier to actually tap a thread in the GRP this giving a tight fit against water ingress but also allowing me to first fit the screw then go inside and fit the nut against a tight screw. Perhaps not good engineering practice in that one thread fights against the other to a degree but certainly more convenient when working alone.
That means the hole must be the appropriate size for the tap. In epoxy then quite a bit smaller. ie a 3/16 hole for a 1/4 inch ww tap. (appologies for the imperial measurments) If the hole is too small the tap will be too hard to start if too big the tap will be too easy. If you rely on the threaded screw cutting its own way in you will need a hole only slightly smaller than the outside of the screw thread. Again if it is too hard to get the screw in make the hole bigger. good luck olewill
 
I took that as meaning you were supposed to use the first drill (i.e. the one in Step 1 that's 1mm smaller diameter than the bolt)? That said, I wouldn't do it that way myself. If it was a relatively lightly-loaded fitting, I'd be inclined to drill it with a drill of the correct tapping drill size for the bolt that I was going to fit in it and then tap it to the correct tread. So, for example, if there was an M8 coarse bolt going into it, I'd go in with a 7mm drill and if it was an M10, an 8.5mm drill. If it was a heavily-loaded fitting, I'd drill a clearance hole through it and put a nut and washer on the inside with a suitable backing plate.
 
Don't like e those instructions or the method at all. and as for drilling a smaller hole than the size of bolt, what's that about!

If your using 10mm bolt, drill 10mm hole, you don't need any stress on the epoxy plug, just compression with a decent backing pad underneath.

Personal I prefer the method where the correct hole size is drilled through the deck, a succession of bent nails held in a drill chuck is inserted into the hole and the core flailed out, epoxy is then injected from underneath till it ouses from above, using a plastic bag like icing cake decoration, seal with masking tape and when hard re drill down from the top. I have pushed softwood dowels,or pencils if using 6mm bolts, through the holes, this helps push the epoxy into the crevices and then when drilling down the drill follows the softwood.

PLank
 
See my post on previous thread via your link.
Agree with PlankWalker. I don't see the need for a smaller hole than the fastener,if you are using a thru bolt & nut-(with backer plate).
Chamfer the top of hole,to allow an "o-ring" of sealant to form around thru bolt.
Also-I understood you were fastening thru a teak deck that is on top of a cored GRP deck.Teak decks can get water between the teak & GRP-from somewhere far removed from this fitting & you should think about trying to seal this second source of leaks.

Again-please re-read my post.Cheers/Len
 
FairweatherDave said:
The method says to drill a hole one drill size SMALLER than the bolt. (image 5). I just wanted to double check that here.
Click to expand...

I can't see that this makes any sense. The hole should be big enough for the bolt to pass through easily.

Depending on how your teak deck is laid, it may be possible for water to leak from under the teak into the hole, so sealant on the underside of the deck would be a good idea.
 
I use a syringe to squirt the epoxy in from above.
put some masking tape on the deck.
Also, if it's a highly loaded thing like a cleat, I stuff the void with chopped glass from a scrap of cloth.
Heating the deck with a hot air gun helps the epoxy flow.
You can clean the syringe with hot water and fairy liquid if you are quick, but they are pretty cheap on ebay.
 
Well thanks to all. I have now done a fair bit of the work on my boat. Len, I never had a teak deck, my contribution on the last thread was only about deck fittings made of teak (ie the grab rails and deflector coaming).
To give my experience here this is what I did......
1. Probably due to cool temperatures (around 10 degrees max) I found syringe from above not very easy (although resin etc had been stored at home indoors). I had added a very small amount of colloidal silica too but looking at the mix thought it should have been syringeable.
2. So I went in from below with peanut butter consistency (as PlankWalker describes) working it into the voids and generally feeling I had not left air bubbles. Afterwards put masking tape on but this was probably unneccessary. (The holes from underneath were made using an inch hole saw as in the diagrams)
3. In the prep phase once I had hollowed out enough room I found an allen key in the drill at slow speed was excellent at removing damp balsa. I would have tried bent nails too had I had any lying about)
4. Re the drill size today I went with the one size smaller approach and found the bolts cut very nicely into the epoxy and as William H says it made tightening up a one man job as the thread just stayed there for me to tighten up the nut. Okay two people would be useful if wanting to put on a lot of torque, but these fittings are relatively light loads.
5. I have used penny washers to spread the load ( and will be using a ply backing pad under a dodgy stanchion).

And for general amusement I forgot the scales on day 2 so mixed epoxy using syringes. I was seconds away from buying some dedicated boat epoxy scales.
Then I left the hairdryer at the boat (not an issue for me but my wife was less impressed today)..... and you can't tell where the resin got wiped off them.
Finally today's issue was a new tube of time expired sikaflex, not as easy to squirt out.... it got messy:). My watch looks okay now as do the cabin floorboards.....
 
FairweatherDave said:
Well thanks to all. I have now done a fair bit of the work on my boat. Len, I never had a teak deck, my contribution on the last thread was only about deck fittings made of teak (ie the grab rails and deflector coaming).
To give my experience here this is what I did......
1. Probably due to cool temperatures (around 10 degrees max) I found syringe from above not very easy (although resin etc had been stored at home indoors). I had added a very small amount of colloidal silica too but looking at the mix thought it should have been syringeable.
2. So I went in from below with peanut butter consistency (as PlankWalker describes) working it into the voids and generally feeling I had not left air bubbles. Afterwards put masking tape on but this was probably unneccessary. (The holes from underneath were made using an inch hole saw as in the diagrams)
3. In the prep phase once I had hollowed out enough room I found an allen key in the drill at slow speed was excellent at removing damp balsa. I would have tried bent nails too had I had any lying about)
4. Re the drill size today I went with the one size smaller approach and found the bolts cut very nicely into the epoxy and as William H says it made tightening up a one man job as the thread just stayed there for me to tighten up the nut. Okay two people would be useful if wanting to put on a lot of torque, but these fittings are relatively light loads.
5. I have used penny washers to spread the load ( and will be using a ply backing pad under a dodgy stanchion).

And for general amusement I forgot the scales on day 2 so mixed epoxy using syringes. I was seconds away from buying some dedicated boat epoxy scales.
Then I left the hairdryer at the boat (not an issue for me but my wife was less impressed today)..... and you can't tell where the resin got wiped off them.
Finally today's issue was a new tube of time expired sikaflex, not as easy to squirt out.... it got messy:). My watch looks okay now as do the cabin floorboards.....
Click to expand...

Ha Ha! Nothing like working in cold temps! Sounds like you persevered & overcame the obstacles.Typical boat work in Northern climate.Our season is so short over here that nobody wants to waste a good sailing day working on boat. Good job! Cheers/Len
 
You must log in or register to reply here.

Share this page

Top