Cutting fiberglass holes

[Mike_J]

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

[hardee]

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

[Mike_J]

Thanks Harvey, A quick search with the right terms and the AND did the trick. Hope to meet you at Friday Harbor!

[thataway]

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.

[hardee]

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

[Robert H. Wilkinson]

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

[Sunbeam]

[srbaum]

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...

[Mike_J]

Thanks for all the great advice!

[Grazer]

[Sunbeam]

[Robert H. Wilkinson]

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.

Regards, Rob

[Sunbeam]

[Robert H. Wilkinson]

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---

Regards, Rob

[Sunbeam]