Another arc at the shore power plug

[Sunbeam]

A trick I've heard of for dealing with screws in fiberglass to prevent cracking-

After drilling the hole, get a larger bit and with the drill going in reverse, run the larger bit over the hole. It takes off some of the gel coat, and is supposed to help with spider cracks.

We may not be talking about the same cracking (not that your tip is not great for dealing with the gelcoat layer). What I was referring to (and I think Roger was too) is that along the length of the hole, unless you drill a very large pilot hole, you are cracking the deeper fiberglass as you turn the screw (not the gelcoat layer on top). It works, but never feels very elegant to me, so I usually do one of three things:

1) Through fasten.

2) Use something that doesn't require a hole (Weld-Mount, etc.)

3) Slightly overdrill and then set (pointy) screw in thickened epoxy. For future removal, you can either wax the screw when you set it in place (then remove, remove wax, and reinstall) or, when the time comes to remove it, touch the head with the tip of a soldering pencil - this heats up the epoxy and you can then unscrew the fastener.

(I usually chamfer the edge of the hole up on the gelcoat if I'm bedding hardware, because not only does it alleviate the spider cracking issue, but it makes a nice little "well" for bedding compound to fill.)

Roger if you were talking about gelcoat cracking then I didn't mean to misspeak for you.

Sunbeam :hot

 

[rogerbum]

A trick I've heard of for dealing with screws in fiberglass to prevent cracking-

After drilling the hole, get a larger bit and with the drill going in reverse, run the larger bit over the hole. It takes off some of the gel coat, and is supposed to help with spider cracks.

We may not be talking about the same cracking (not that your tip is not great for dealing with the gelcoat layer). What I was referring to (and I think Roger was too) is that along the length of the hole, unless you drill a very large pilot hole, you are cracking the deeper fiberglass as you turn the screw (not the gelcoat layer on top). It works, but never feels very elegant to me, so I usually do one of three things:

1) Through fasten.

2) Use something that doesn't require a hole (Weld-Mount, etc.)

3) Slightly overdrill and then set (pointy) screw in thickened epoxy. For future removal, you can either wax the screw when you set it in place (then remove, remove wax, and reinstall) or, when the time comes to remove it, touch the head with the tip of a soldering pencil - this heats up the epoxy and you can then unscrew the fastener.

(I usually chamfer the edge of the hole up on the gelcoat if I'm bedding hardware, because not only does it alleviate the spider cracking issue, but it makes a nice little "well" for bedding compound to fill.)

Roger if you were talking about gelcoat cracking then I didn't mean to misspeak for you.

Sunbeam :hot

Nope - you hit the nail (or screw in this case) on the head. In addition to the the possible gel coat and fiberglass cracking issues, I've also had a screw break off in fiberglass because I didn't drill the hole large enough and had a number of factory screws pull out because the holes were too large or too shallow. Hence, IMHO, screws directly into cured fiberglass are an "iffy" proposition and there seems to be more ways to screw it up than to get it right (of course that's true in many endeavors). So like you, I prefer to through bolt when possible. I do chamfer the through bolt holes but I use a countersink drill bit to do that.

 

[Sunbeam]

At least I'm not the only one!

I realized that I left off one way I sometimes use, which is (for a blind hole) to drill and tap for a machine screw (that does not go all the way through to accept a nut).

 

[rogerbum]

At least I'm not the only one!

I realized that I left off one way I sometimes use, which is (for a blind hole) to drill and tap for a machine screw (that does not go all the way through to accept a nut).

What size machine screws have you done this with? I can see it working well for 1/4-20 or larger thread sizes but I guess I'd be afraid to try it with say 6-32 or 8-32 as I'd worry about it pulling the internal threads out of the glass. However, I suppose if you have enough depth to the hole, it would work pretty well.

 

[Sunbeam]

What size machine screws have you done this with? I can see it working well for 1/4-20 or larger thread sizes but I guess I'd be afraid to try it with say 6-32 or 8-32 as I'd worry about it pulling the internal threads out of the glass.

I haven't done it with any smaller screws (6,8 ). The other thing is that usually (was trying to think if it was always?) I'm going into new, thickened epoxy, not existing fiberglass/polyester. It's been some time (since previous boat), so my memory is a bit foggy on details. That said, ask me in a week! I'm about to tap a bunch of holes for my trim tabs (tho' those will be 1/4-20), but also I'm going to first try tapping the holes for the #10 screws to fasten my new drain plug. That will be into 50% existing fiberglass and 50% new fiberglass. I'm not sure the holes are going to be deep enough to work really well, so my fallback is to just run them on through and use nuts and washers. I was actually figuring on doing that in the first place, but the new glass plus the old glass turned out to be thick enough that I'm going to try tapping first in the spirit of experimentation.

I still don't really favor blind holes, but sometimes they do seem to end up as the best choice.

Sunbeam

PS: I just remembered that I did tap into glass/polyester to fasten some seacocks, although it was new backing blocks not old work. That wasn't small screws though - if I remember correctly they were 5/16" They seemed to tap well however.

 

[Captains Cat]

Just got my smart plugs in the mail! Thar receptacle is one HEAVY sucker! Should correct our starboard list! :wink:

Charlie

 

[rogerbum]

Just got my smart plugs in the mail! Thar receptacle is one HEAVY sucker! Should correct our starboard list! :wink:

Charlie

I don't know about that. From where does that starboard list come? Aren't you normally at the helm? :wink: :lol:

 

[Captains Cat]

Just got my smart plugs in the mail! Thar receptacle is one HEAVY sucker! Should correct our starboard list! :wink:

Charlie

I don't know about that. From where does that starboard list come? Aren't you normally at the helm? :wink: :lol:

Hey, I resemble that remark. Since we last saw each other I've lost about 25#! That's a goodly portion of a 'box 'o Bumgarner's'. See if you get birthday greetings initiated by MOI next year!

 

[thataway]

I prefer a counter sink to a larger drill bit, run in reverse, to chamfer the edges of the hole and prevent glass splintering. The drill and tap method depends on the thickness of glass. I have done it, with smaller screws, in thicker glass panel. The counter sink is much less likely to grab the edge of the glass, and will give a smoother edge. I keep a counter sink in each of my sets of drill bits. Also the pilot hole has to be the correct size for the screw size and type.

 

[Sunbeam]

I prefer a counter sink to a larger drill bit, run in reverse, to chamfer the edges of the hole and prevent glass splintering.

That's what I generally use too, most of the time (conveniently, I have a cordless drill with THE MOST irritating chuck, so I just leave the countersink bit in it all the time to avoid getting irritated with it ). But sometimes I will run a drill bit backwards - like say with a hole saw because my countersink bits aren't that large, or even with a regular bit occasionally (can't think of a good example now, but there must be a reason!)

But it's the (comparatively) large pilot hole for a pointy screw into fiberglass that never really feels that great to me. Especially since that often seems to be into a not-very-thick layer of glass.

I always enjoy reading about other people's problems and solutions, because there are so many different ones (and different workable solutions). It's never boring and I always learn something (and sometimes get that "yup" camaraderie feeling too) :thup

Sunbeam

 

[rogerbum]

Just got my smart plugs in the mail! Thar receptacle is one HEAVY sucker! Should correct our starboard list! :wink:

Charlie

I don't know about that. From where does that starboard list come? Aren't you normally at the helm? :wink: :lol:

Hey, I resemble that remark. Since we last saw each other I've lost about 25#! That's a goodly portion of a 'box 'o Bumgarner's'. See if you get birthday greetings initiated by MOI next year!

Congrats on the weight loss. I've had some health issues (pinched nerve in my back that's almost now healed) that prevented me from running for awhile so I'm going in the other direction lately. So I think the starboard list might have been transferred from your boat to mine.

 

[olsurfdog]

Wow, As it turns out I'm on my way out to do this very project. In the fall I removed my fuel tanks to refasten them and install a new kicker mount and swim platform. Like Sunbeam I would prefer to thru bolt, it just feels more secure to me but for this part of the job it also seems like over kill. The bracket and platform will be thru bolted but while I was at it I removed the fish finder and speedo sensors to refasten them correctly. They were fastened with # 6 or 8 screws in holes in transom and silicon as bedding. To be sure to get all silcone out I over drilled the holes to 1/2". I did this in 3 or 4 steps ( ie with 1/4 then 3/8 drills to try to be sure to get all silcone residue in the hole out,then undercut with the dremel bit). I use an old and dull countersink bit to chamfer the hole. Now I'll drill the pilot hole with a bit at least the same diameter as the screws root. This is bigger than you would use in wood but it allows the screw to go in with out cracking the epoxy. There's no science about the bit size its more or less by feel with test holes in a piece of hard wood. Then I pretap the hole with the screw, I don't worry if the hole is a little big as long as the screw gets some purchase. Then remove screws fill the hole with some 5 minute epoxy from the hardware store, allow it to set up, coat the screws with a thin coat of grease and install the fitting with the appropriate bedding compound. I try to do this before the 5 min.has completely hardened. This has worked well for me in the past-- mostly I use West epoxy but the 5 min comes in syringe and meters the epoxy evenly for such a small amount.
I try to use thickened 5 min. whatever I have on hand even thicken it with silica or micro fibers. With 5 min. you have to move along but it's nice to be able to finish up the job right away. Snug things up and them come back in an hour or two and tighten.
Michael

 

[Sunbeam]

If you like using the 5-minute, but would prefer not to use "just" hardware store epoxy, WEST System does make G/5, which is fast. Also nice for screws and things (but not fast) because it's a bit more flexible and can be easily mixed in tiny batches is G/flex, also by WEST. I haven't used the G/5, but I do keep a couple of small containers of G/flex on hand (it's one to one mix and the containers have those tapered, restaurant-ketchup-squeeze-bottle type tops).

http://www.westsystem.com/ss/specialty-epoxies/
Sunbeam

 

[olsurfdog]

Thanks, I'll have to check it out- sounds like just the ticket. Small amounts are always a problem also nice if it doesn't harden to much.
In rereading my post I left out the part where I fill the 1/2" hole with thickened epoxy allowing to harden and then drill the pilot hole for the screws.
Michael