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Old 06-26-2021, 07:38 PM   #1
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Drilling/grinding fiberglass/epoxy

Hello fellows,
Was wondering if anybody would have any hint about drilling/grinding fiberglass/epoxy?
1. I have a crack in my fiberglass bow pulpit, I want to grind it and fill it with epoxy and fiberglass strands. What kind of disk to use to grind cleanly the crack?
2. I am redoing my anchor capstan fixation. My plan is to drill oversized fixation holes, fill them with thickened epoxy and drill proper holes through the epoxy. I already drilled through epoxy but was wondering about any tip for clean hole, like drill slow vs drill fast etc.

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Old 06-26-2021, 08:12 PM   #2
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For minor grinding I use a Dremel with a grinding bit. For larger jobs I use a Roloc disc on a right angle drill. I use about 30 grit discs on the Roloc adapter. They cut very well and change quickly. The right angle drill allows much more control than a regular drill since it isnít so far away from the work surface.
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Old 06-26-2021, 08:39 PM   #3
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Quote:
Originally Posted by Comodave View Post
For minor grinding I use a Dremel with a grinding bit. For larger jobs I use a Roloc disc on a right angle drill. I use about 30 grit discs on the Roloc adapter. They cut very well and change quickly. The right angle drill allows much more control than a regular drill since it isnít so far away from the work surface.
Thank you David, tonight I learned something! I did not know what is a roloc disk, now I know

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Old 06-26-2021, 08:53 PM   #4
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I love the Rolocs for grinding fiberglass, they cut quickly and with the right angle drill are pretty easily controlled. I get them on Amazon.
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Old 06-26-2021, 08:55 PM   #5
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I love the Rolocs for grinding fiberglass, they cut quickly and with the right angle drill are pretty easily controlled. I get them on Amazon.
Would you have a link to the one you get from amazon? there are a ton of them!

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Old 06-26-2021, 09:02 PM   #6
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I looked and the ones I use are 50 grit and currently unavailable, like a lot of things.

3M Green Corps Roloc Discs, 3'' - 50 Grit DISC ROLOC 50GR 3 25/BX GREEN
Brand: 3M
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Old 06-27-2021, 01:33 AM   #7
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Is the crack of cosmetic concern, or structural concern?

"V'ing (More like U'ing) out a crack" and filling is great for cosmetic repairs, especially shallow ones in gelcoat, e.g. crazing.

But, if it is structural, you need to feather a wide area around the crack and build up layers of glass to fill. Going 12x the depth of the crack around it is fairly typical. Then you put sheets of fiberglass back in, saturating them with epoxy, working from large pieces to small pieces to fill the hole to the correct shape, building a few sheets at a time to avoid excess heat while the epoxy cures.You may also want to drill holes at each end (and fill with the rest) of the crack before starting to interruot the propagation.


Happen to have a picture?
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Old 06-27-2021, 01:33 AM   #8
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Donít forget the adapter.

Pro 3" Roloc Disc Pad Holder - 1/4" Shank
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Old 06-27-2021, 06:01 AM   #9
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Instead of drilling a hole and sticking a bolt in it the local ACE should have a bronze bushing to fit the bolt .

The bushings will help the deck when the hold down bolts are tightened , and as a high load item the extra diameter of the bushing will also be a help in not moving..


Auto body discs come in a course enough grit to make fast work of a small grinding job.
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Old 06-27-2021, 07:33 AM   #10
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Quote:
Originally Posted by gkesden View Post
Is the crack of cosmetic concern, or structural concern?

"V'ing (More like U'ing) out a crack" and filling is great for cosmetic repairs, especially shallow ones in gelcoat, e.g. crazing.

But, if it is structural, you need to feather a wide area around the crack and build up layers of glass to fill. Going 12x the depth of the crack around it is fairly typical. Then you put sheets of fiberglass back in, saturating them with epoxy, working from large pieces to small pieces to fill the hole to the correct shape, building a few sheets at a time to avoid excess heat while the epoxy cures.You may also want to drill holes at each end (and fill with the rest) of the crack before starting to interruot the propagation.


Happen to have a picture?
Not really structural as at the end of the pulpit, just a crack that I want to fill in to avoid water ingress that would permanently damage the internal plywood.

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Old 06-27-2021, 07:35 AM   #11
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Quote:
Originally Posted by FF View Post
Instead of drilling a hole and sticking a bolt in it the local ACE should have a bronze bushing to fit the bolt .

The bushings will help the deck when the hold down bolts are tightened , and as a high load item the extra diameter of the bushing will also be a help in not moving..


Auto body discs come in a course enough grit to make fast work of a small grinding job.
I was also looking at using bushing of some sort, if I find some of correct length and material I will use this.

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Old 06-27-2021, 07:37 AM   #12
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Quote:
Originally Posted by Comodave View Post
Donít forget the adapter.



Pro 3" Roloc Disc Pad Holder - 1/4" Shank
Have we already met? How come can you know how much silly I am? Of course I could have forgotten the adapter lol
Thank you for the reminder!

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Old 06-27-2021, 09:54 AM   #13
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I use a laminate router with a cone shaped bit to run down the cracks making a vee shaped groove then fill with epoxy and high density filler (404). Depending on location you may want to back it up with a strip of glass fabric under the crack.
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Old 06-27-2021, 10:00 AM   #14
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I use a laminate router with a cone shaped bit to run down the cracks making a vee shaped groove then fill with epoxy and high density filler (404). Depending on location you may want to back it up with a strip of glass fabric under the crack.
Good idea, did not think about using the router.

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Old 06-27-2021, 10:06 AM   #15
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You may want to do something similar with drilled holes only just use a countersink. I do this with all my deck fittings, drill, countersink, apply nonthickened epoxy then make a ring of butyl around the bolt to squish into the tapered hole when tightened.
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Old 06-28-2021, 05:49 AM   #16
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Bushing for bolts,,,"if I find some of correct length and material I will use this."

An auto body grinder can shorten a bronze bushing very rapidly.
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Old 06-28-2021, 12:54 PM   #17
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For the Roloc, if you have an air compressor on board, you can drive it easily with an air powered die grinder. If not, you can use a battery powered die grinder like my favorite Milwaukee tool. Drills really aren't made to do that and generally turn too slow for grinding.

For cosmetic cracks, the smaller you have to grind out the better. A small diamond or carbide burr in a dremel to trough out a crack minimizes the area size while creating a surface for the epoxy to stick to.

I would not used fiberglass strands for cosmetic repairs, colloidal silica would be more appropriate (for a high traffic area) or even micro bubbles (for low traffic areas).

The question will be, how are you going to finish the repair? If you plan to use gel coat to match an existing color/sheen then epoxy based fillers is probably not the right choice. If you plan to paint then it's fine.
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Old 06-28-2021, 01:24 PM   #18
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Rolocs work great. Iíve used them on car projects and on the boat. Harbor Freight has them for very good prices too.

https://www.harborfreight.com/pack-o...CABEgJGT_D_BwE
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Old 06-28-2021, 04:51 PM   #19
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For the Roloc, if you have an air compressor on board, you can drive it easily with an air powered die grinder. If not, you can use a battery powered die grinder like my favorite Milwaukee tool. Drills really aren't made to do that and generally turn too slow for grinding.

For cosmetic cracks, the smaller you have to grind out the better. A small diamond or carbide burr in a dremel to trough out a crack minimizes the area size while creating a surface for the epoxy to stick to.

I would not used fiberglass strands for cosmetic repairs, colloidal silica would be more appropriate (for a high traffic area) or even micro bubbles (for low traffic areas).

The question will be, how are you going to finish the repair? If you plan to use gel coat to match an existing color/sheen then epoxy based fillers is probably not the right choice. If you plan to paint then it's fine.
Paint it will be.

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Old 06-28-2021, 05:21 PM   #20
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My right angle drill works great with the Rolocs for grinding. It is plenty fast IMO. Really wouldnít want it to be any faster since it removes material quite fast.
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