I attached the starboard forward side panel last night on my weekender and although most of the evening went well, I ended up with a bit of a conundrum. I did not pre drill counter sunk holes for the screws as I figured they would pull down into the 1/4 inch ply.
Unfortunately, I was wrong. :oops:
And I've discovered that it's not good to come up with a new plan once the epoxy is mixed. So, now the epoxy is nicely cured, and I have many screw heads sitting proud on the side panel.
Do I simply take them out and fill the holes? I figure the epoxy is plenty strong and I will be glassing the hull.
Thoughts?
Thanks,
Steven Goodman
Just remove the screws and fill the holes. It is alright. Press on
Depends on how confident you are regarding how well the surface veneer of your ply is glued to the other plys. Glue is only a surface fastener so if you plywood pulls apart you have a problem. Screws hold all the layers together and in my experience it is good to leave a couple in (though i still remove a majority of them myself). One incident in particular comes to mind on a boat where I removed all screws I could to save weight. One of my 3/4 inch stringer supports for a seat split near where it was glued to the plywood seat. Something that wouldnt' have happened if a mechanical fastener was in there.
Another way around the problem of no mechanical support is to make a small cup over the screw hole with duct tape and pour epoxy into the cup intell the hole is filled and there is surplus epoxy in the cup (monitor this as the poxy will soak into the wood) and let it cure. Then remove the tape and sand the overfill flat. This will act like a screw and provide mechanical support to the entire ply structure. I wouldn't do them all this way. Invest in an adjustable countersink for your most used screw size.
Remove the screw and lightly hit the hole with a large diameter drill bit to splay out the top part to a counter sink profile. Then replace the screw.
I would simply invest a few $ in a #8 adjustable counter sink with a couple spare drill bits for it. Vermont/American makes one that is quite inexpensive and good quality. Available at ACE Hardware stores and a lot of others. You are going to be using it so much from this point on it will really make the job progress a lot faster, easier and more accurate. When it comes to drilling thru the 1/4" panels you will have a lot of issues with trying to countersink them with just a larger drill bit. Even with a depth stop on it. Aside from the angles being wrong on the sides of the drill bit the tearing out from not being able to center it accurately will make you tear your hair out not to mention doing a lot of repair/filler work.
Pulling all the screws and filling with epoxy plugs isn't really practical but it can be done. Getting thickened epoxy injected with a syringe so it won't run out of the holes is a big challenge. The resulting plug just doesn't work as well as a mechanical fastener in the same place.
Lots of excellent advice as always.
Thank you.
I think I will remove some of the worst offenders and use my countersink bit to redrill some of the other ones.
Yes, I do have an adjustable countersink bit already. Just didn't use it. I found it slowed down the process a lot on the earler stages and it was just easier to drive the screws into the wood with out pre drilling everything. I think that was okay for the thicker ply but this 1/4 inch stuff I'm using is quite hard.
I'm not using marine ply. The 1/4 inch ply is actually designed to be exterior underlay. 5 beautiful veneers with waterproof glue!! And pretty cheap too. Too bad it only comes in 1/4 inch.
Thanks again. I'll post some pics when I get the sides on.
Steven Goodman
Pre-drilling can be a pain, I know......I predrilled and counter sunk every screw on my Mini-Cat. But hey, when you have a good chemical bond held together with a good mechanical bond you have little to worry about.
It may take a while to pre-drill & countersink, but it's worth it...........at least for the screws your going to leave in.