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  #1  
Old 10-26-2011
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What to use to grind/sand fiberglass?

I'm about to start a few practice fiberglass projects over the winter before doing real work on my boat. All the books talk about grinding down fiberglass/epoxy with an angle grinder, but I can't seem to figure out what sort of disk to use- my hardware store stocks metal grinding disks and masonry disks, but none specifically for fiberglass. Also, will my regular orbital sander work for finishing?
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Old 10-26-2011
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Right angle grinders? Those are for removing lots of material in short order. Like welds. Most stone type wheels clog real quick because of the high rpms when used on wood, or glass. Sanders come in the same right angle type but with lower rpms. (also used for polishing) Suggest 7 - 9" dia
Large surfaces like a deck or hull will become wavy from using right angle grinders also. (the larger the disk the flatter it can lay on the surface) Random orbit sanders (a great invention!) take less from a large area while keeping the disk flat, but take hours and hours to remove large amounts of material In all cases the sandpaper needs to be changed often since gelcoat and substrate are much harder then wood.

"Fairing" Is the making or prepping of a surface fair smooth like a table top, or fair like the curves of a boat, airplane, or car. (no ripples or dibits) is easier to maintain the fairness of a surface then fix the damage done from heavy grinding of a surface. You might take a trip to an auto body shop and watch how they work to keep the surface "fair" on cars being repaired.
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Old 10-26-2011
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I have a full collection of 5" and 6" random orbit and a 9" 24 grit disk for heavy repiars along with with a few sheet sanders for real fine work


If i had to use just one it would be the 6" with the vacume as the glass dust gets every place BUT it would take forever when grinding away places that had a lot of old glass tape to remove and replace
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Old 10-26-2011
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Chris

Tommays hits the nail on the head, but casually mentions the dust....if you are doing this in an enclosed space, wear a mask, and use the vacuum....his picture also shows the face shield....I wear glasses and still use goggles or shield...much cheaper than replacing a lens that gets spiked or liquid on it....let alone your eyes...

My favorite is a 6" grinder, too, with 60-200 grit paper then I switch to a palm sander for the finer finish stuff. As an old gear head, then I switch to a hardwood hand stick about 12-14" long by 1.5-2" square wrapped in sandpaper for the flat finish stuff.

Shop an auto parts or online for sandpaper, buying it at home stores will cost you dearly.

Good pic Tommays, I love it when tools are used...

Best of luck...
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There are a lot of ways to skin the cat -- and you may have to try out several different ones to find out what works best for you and the project at hand.

RO sanders are great for fairing and final prep before painting, but as Denise mentioned they aren't real fast or efficient at taking off a lot of material.

For big grinding chores, it's hard to beat a right-angle grinder/polisher with an aggressive grit (like 36.)

For smaller jobs (like grinding back through hull openings to glass them over) I usually reach for a 4-1/2" high-speed angle grinder with a flapper wheel instead of a grinder wheel.

Please take careful note of the recommendations above about dust -- those are dead on accurate. A vacuum will help a great deal, but anything you can do to isolate the area in which you are grinding will pay off when you start to clean up. In addition to the safety glasses/goggles/face shield and dust respirator, think about buying a Tyvek bunny suit and a painter's head cover. All those small pieces of ground up glass will get into your pores and bug the bejeebers out of you.
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Lightbulb

Plus one or two or three on wearing breathing protection and even a tyvek suit.
Also, after spending too much time on my initial grinding with some 80 and 60 grit, an old boat builder told me to use 16 grit disks. Wish I'd known that sooner!
I would put the intake for the 3" vacuum hose right in front of the out-fly from the spinning disk. Worked great.
For finishing, get yourself a "dustless" sander like the small Fein, and put that hose right on the hose fitting on your quarter-sheet sander. After many years with the Makita, I changed to a Bosch, and the paper holding mechanism works way better on it.

"Git Er Done!"

LB
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Thanks guys. I'll make sure to wear enough safety gear to make the neighbors think I'm running a meth lab in my shed.

So for creating a bevel when reinstalling a deck skin after a core repair, what would be your weapon of choice?
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1) Place a fan directed to blow the grinding dust away from their face, low speed is usually enough, just enough to make the dust flow away

2) Tape the wrists and ankles to seal the tyvek suit.

3) Use a Tyyvek hood

4) wear shoes that you will never need again - old tennis shoes ready for the trash are perfect. I think our grinders buy old tennis shoes at swap meets and garage sales.

5) Of course, get the best dust mask possible.
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Old 10-27-2011
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Flap wheels on a 4 1/2 inch sander are what I use to do the bevels, this type:

Shop 3M: Flap Disc

Note, these are normally called 'disks' not wheels. Often if you ask for a flap wheel you'll get one that's designed for sanding/grinding with the edges, not the face.

Typically, I schedule grinding for cool days, and if possible leave them for spring or fall so the heat doesn't get to you when wearing all the 'dust proof' gear.

Most important is the dust mask and goggles, an old dive mask will work, you don't want the dust in lungs or eyes.

To contain dust I lay old blankets out, the fibers seem to trap more of the dust than plastic sheeting.
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info source

Chris,

The link below is an excellent resource - inluding several how-to videos. Very helpful, knowledgeable and experienced people on the technical help line as well.

Good luck!
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