Cutting fiberglass holes

M

Mike_J

New member
I am planning to make a couple of holes in the interior fiberglass soon... One is to add a hatch to the v-berth (I will use one of the lazarette covers I replaced this week) and another is to install some speakers.
I would appreciate any advice on cutting the fiberglass holes. Tools and techniques?
Cheers
Mike
 
Mike, I'm not (by any means) a pro at cutting or working fiberglass. There is considerable info on the site about how to do it. I would do a search, (the button is at the top on the right side. Click on search and then put into the top right box, "Cutting AND fiberglass", or "drilling AND fiberglass" and you will probably get tons of threads.

There is probably plenty of stuff on UTube too, but I don't know for sure.

We have several folks on the site who are considerably expert at what you are wanting to do, and most of them have posted it several times. Look at the search or look through the forum index for appropriate threads.

Good look.

Harvey
SleepyC :moon
 
Many like to put tape over the area to be cut first. If you are going to use round holes--then a hole saw--I have a collection of about 20 over the years from 5/8 to 5" in diameter. They last well if you buy quality (Not HF),

I like to drill the pilot hole first, then put the 1/4" bit of the pilot in place, and run the saw backward to avoid splintering or cracking the gel coat, until the gel coat is well scored. Then go forward--I often will go slightly over half way, then go to the reverse side to finish the cut. You can use extension bits on the main shank--I have cut holes as long as over 24" for a shaft log.

A Fein type of saw will work for straight cuts. A Rotozip will also work-but be careful about control, and consider using a templates. A saber or jig saw can be used with a very fine tooth blade. Be careful because many cut on the up stroke and can splinter the gel coat. Go slowly and with little pressure. Use quality bi-metal blades, Don't let the blades get too hot, and change blades when they are dull. I have also used a small circular saw with carbide blades on some areas--as well as a carbide tip router, again with templates--many ways to do it correctly.

Always wear a respirator, cover your eyes with goggles, wear a suit to avoid getting glass splinters on your skin. Use a vacuum to collect the dust on a regular basis. Remove or cover any near by cloth upholstery.

For the hatches, often it is easy to use a hole saw for the corners, and then lay straight cuts for the sides. You can tape batons on the glass to be sure that the cut is straight and guide what saw or divide you use on that. straight edge. You want to slightly round the edge after you have made the cut with sandpaper, to remove any sharp edges.

Seal any core which is exposed with epoxy.
 
Mike,

Follow those directions and you can't go wrong.

Would love to meet you at FH or between somewhere. I usually leave Sequim very early to avoid the morning winds in the Strait so if it is nice on that side, run up and around the E and N ends of San Juan Island, looking for the Orca. Would not be hard to meet up in those waterS.

Harvey
SleepyC:moon
 
After drilling small holes for thru bolts etc. I was told to use a counter sink drill in reverse to chamfer the edge. This helps prevent the edge of the gelcoat from chipping and also from radial stress cracks forming.

Regards, Rob
 
Robert H. Wilkinson":2qe9wj6t said:
After drilling small holes for thru bolts etc. I was told to use a counter sink drill in reverse to chamfer the edge. This helps prevent the edge of the gelcoat from chipping and also from radial stress cracks forming.
Click to expand...

I do this too. For the gelcoat reason and also because it makes a nice little well for bedding compound. I run mine in forward though (with the countersink bit) and haven't had a problem (may depend on the specific bit one has though). I will sometimes make a chamfer just after my pilot hole, but before drilling the main hole, for the same (gelcoat) reason. Then I may go back and re-chamfer the main hole afterward.

Fun to read how others go about things - I always pick up good tips :thup

Sunbeam :hot
 
Rob is absolutely correct. Holes for fasteners should be countersunk (while the tape is sill over the hole), as this will help to prevent the gelcoat from chipping. A very handy tool for this and future jobs (for the do it yourselfers) is a book call This Old Boat, by Don Casey. It is very handy even if you are not a sailor...
 
Robert H. Wilkinson":abst9oke said:
This helps prevent the edge of the gelcoat from chipping and also from radial stress cracks forming.
Click to expand...

I have noticed, looking quite closely, at some of the fasteners around my boat, that there appears to be some small hairline stress cracks in the gel coat. Is this a concern I should address? If so how would one go about it?

Thanks,
Grazer
 
Grazer":2n32p2tb said:
I have noticed, looking quite closely, at some of the fasteners around my boat, that there appears to be some small hairline stress cracks in the gel coat.
Click to expand...

Presuming these are the typical cracks you see (radiating out from the fastener hole), then they are often caused by "pointy screws" being put into "straight-drilled" holes. If the original hole had been chamfered at the top then likely there would be no crack(s). If you wanted to completely repair them, you would have to eliminate the cracked gelcoat ("V" it out, or etc.) and then re-gelcoat.

So far on my boat all of these cracks have been hidden under hardware bases, so what I do is when I have the hardware off to re-bed (and also over-drill/fill), then I chamfer the new hole, and that takes care of most of the cracks. If there are any still remaining (but they are still going to be under the hardware base), I will lightly chase them out (make a very slight "V") and just let the bedding compound fill them (it's a very very shallow V).

They are likely to be "just" (I put that in quotes because once you start repairing cosmetics they no longer seem like "just"!) cosmetic if they only are in the gelcoat. There can be gelcoat cracks that reflect cracks in the underlying fiberglass and/or some stress that should be addressed (like say around stanchion bases with inadequate backing) but you can usually sort of tell if you think about what force has been applied to the item. A small screw into a hole for a lightly loaded piece is likely to have been caused by the "pinch" at the top of a straight-drilled hole.

A side benefit of chamfering is that it makes a pocket for an extra little bit of bedding compound.

Sunbeam

PS: If you post photos of the cracks you are describing we might be able to say more definitively.
 
Robert H. Wilkinson":ldv0rh4l said:
As well as V ing out a crack prior to making a repair you should drill a hole at the end of it - this prevents the crack from spreading further.
Click to expand...

I've never done this in fiberglass (I have made larger repairs, but then the repair itself eliminates any need for a "stop hole" ). Do you do it even with very small, won't-be-stressed-anymore-now-that-the-hole-has-been-chamfered, cracks like you'd find around fastener for a piece of hardware? As an example: I have a bimini fitting with two fastener holes. Into un-protected balsa core, of course :wink:

So what I do (regardless of whether or not there is any fine hairline crack) is overdrill the hole (removing core), then fill with thickened epoxy, then re-drill the fastener hole in the center of the new epoxy annulus. About 80% of the time, this also eliminates any small cracks (they are subsumed in the epoxy filled area). The other 20% of the time there remain one or two tiny, tiny hairline cracks (they type you can't even feel but can see if you look closely), which are no longer connected to the fastener hole at all (because of the epoxy). They are still (just barely) under the hardware (bimini bracket in this example). I still V them slightly, just because I think it's good form. This all stays under the bracket, and the V is very very shallow and fine.

However, if I were to then drill a hole at the end of the V, it might be outside the bracket. So then I'd have an additional gelcoat repair. Also, if I actually drilled a hole, there would be core to seal. I wonder if this is necessary, since there is no longer any particular stress on the former hairline spider crack, now very shallow V.

Here is a photo of one set of bimini bracket holes. You can just see a small "leftover" crack at the top of the left-hand hole in the tan area. After the photo was taken, I lightly "V-ed" it. But I can't see how this would need a hole drilled. Is it going to be stressed at all? Maybe so and I just can't "see" it in my mind...

By the way, this was photographed so close up that it makes the chamfers look HUGE. They actually aren't - they're just normal sized.

bracket_holes_re_drilled_and_chamfered.jpg


Sunbeam
 
Sunbeam, in your example I don't think you need to worry about drilling. It should be fine repaired as you describe. That is a practice I learned in machine shop. Just figured if it works to stop a crack on a engine block it should work on other things. I do this when repairing polyurethane bumpers at work. If the open edge of a crack has spread a bit - drilling the closed end of the crack relieves pressure and the crack will close back up(slightly). We also sometimes drill holes about a quarter inch apart all along the length of the crack - then the 3M repair material we use is forced into the holes, then the V filled, then more is applied to the back side along with a reinforcing patch(like drywall tape-the kind that looks like strings). This way the repair material is "stitched" together front to back by way of the material in the holes.

Anyway,,, back to boats - probably in most cases a small hole drilled just through the gel coat would suffice. No need to drill into the core - although I suppose if the crack included or extended to the core it would need to be sealed anyway. On boats it is not always possible to access the back side of a repair.

If only the "professionals" did things properly in the first place--- :cry

Regards, Rob
 
Robert H. Wilkinson":x44f6lj5 said:
Sunbeam, in your example I don't think you need to worry about drilling. It should be fine repaired as you describe. That is a practice I learned in machine shop. Just figured if it works to stop a crack on a engine block it should work on other things.
Click to expand...

I do understand it on metal and things of that nature. My sense is that it's not necessary with fiberglass, presuming one is making a "proper" repair for the material at hand already. However, I always like to hear how other people approach repairs :thup

Robert H. Wilkinson":x44f6lj5 said:
If only the "professionals" did things properly in the first place--- :cry
Click to expand...

Occasionally another "emoticon" or two gets added to the mix when I'm reasonably sure no-one can hear me :wink
 
V ing out the crack if it is a superficial craze is proper before filling with gel coat--fibers if a large crack--glass over if there is actually stress in this area. I agree, that fiberglass is not like plexiglass or metal needing a "stopper hole" drilled.

The small craze cracks are usually due to lack of proper installation of the screw, and as long as no core is compromised, not really an issue.
 
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