Anyone Ever Use A Router On Fiberglass?

[Carl Thunberg]

I'm installing a garboard drain on the next warm day. Everything I've read on this topic says to use a grinder and a Dremel tool to grind out a depression for the garboard drain flange so it sits fair with the keel. Coat the drain with wax, then epoxy the depression to make it even, using the drain as a form. After the epoxy sets, remove the drain, pre-drill the screw holes, seal the garboard drain and screws with 4200 (5200?) and you're done.

Being a pretty fair woodworker, but with no significant experience with fiberglass, I have to ask. Wouldn't the whole process be much simpler if you cut a jig out of plywood with a hole in the center, installed a collet on your plunge router and set a rabbeting bit at the correct depth. One trip around the jig and VOILA! A perfectly round hole of the exact depth required for the garboard drain flange to be fair with the keel. No epoxy required. Just apply your marine sealant and go.

I guess my question boils down to this. Will fiberglass shatter, or can it be cut with a brand new router bit? Unfortunately, I don't have the opportunity to try this on a test patch first.

[s-dupuis]

Carl,

I have cut fiberglass successfully, with no cracking, using a Roto-Zip tool. Roto-Zip is like a mini router that is slightly larger than a Dremel tool. It is high speed and has an adjustable depth guide. They are typically used for cutting holes in sheetrock walls. The bit is about 1/8" diameter and can plunge (drill) in as well as cut laterally.
Because it is smaller overall it can get into tight spaces. A circle template can be made from wood to cut perfect holes.

Steve

[Bill Goldsmith]

I think you would save a bunch of time if you just started the hole with the right diameter forstner bit (I am guessing 2") and only take that depth down to the thickness of the flange on the garboard drain. The forstner bit will leave you with a nice center depression that you can use to guide the smaller bit for the through-hull hole.

It's probably not a bad idea to seal the exposed gelcoat and laminate with epoxy anyhow, before final installation of the drain, to ensure no water intrusion. I would seal the entire hole from the outer skin all the way to the bilge.

[Gary H]

Last year, I removed most of the aft deck on my Ty to replace rotted balsam core. I used a 1/8 inch carbide router blade to cut the perimeter of the fiberglass area to be removed. Worked just fine. I would recommend wearing a respirator.

[jbenagh]

I think the rabbeting bit would leave a pretty serious stress riser at the inside edge of the rabbet. This is one of the rare cases where removing more material will make a stronger joint. I thought this was in the West manual but I cannot find it.

I think the instructions you mentioned are right -- you want a bevel in the fiberglass backfilled with thickened epoxy. The gentle bevel will not have as many cut glass fibers at a high stress point. In fact the stress should be even -- the epoxy (probably thickened with silica -- West 406?) will distribute the load across the large beveled area.

I've fixed exactly one fiberglass boat, so make of this what you will.

[Carl Thunberg]

I think a 2-inch For$$$tner bit may be a bit pricey. The biggest Forstner bit I have is a 1-inch bit and I think it cost me about $30. I'm also worried I won't be able to control the depth very well. I like the Roto-Zip idea. I was so fixated on the router that I forgot all about my Roto-Zip. Jeff, thanks for the input on the stress concentration on the vertical edge. I think I'll use a combination of the Roto-Zip to hog out the majority of the fiberglass and get a nice flush bottom. Then I'll take my grinder to taper the edges. With that in mind, I guess it doesn't matter if the gelcoat shatters a little bit. I'll be grinding the edges anyway. And yes, I will be wearing a respirator. Thanks again. Now I need a nice warm day in the 40's.

[Steve Laume]

Carl, the router with a jig and collet will do a fine CONTROLLED job of mortising in your drain flange. The fostner bit will leave you to try to stop at the correct depth. If you are worried about a stress point, you could use a core box bit with a radiused end. A carbide router bit loves fiberglass. I have a roto zip tool but feel it is kind of over rated, Steve.

[drysuit2]

I have used a router on glass. I covered the area with blue masking tape to keep the tearing to a minimum. You will destroy a nice router bit. So be prepared. But it cut a nice controlled hole. And wear your respirator.
Hope this helps

[S/V Necessity]

Harbor freight sometimes has the larger bits *real* cheap. They are not fine German bits, but they do work, remarkably well for the price. In fact they are perfect for jobs that will be hard on the bit... disposable!

[winthrop fisher]

hey hows ever thing going,
don't use 5200 use 4200 and as far as the bit, it looks good or you could use a hole saw....winthrop