Grinder / sander recommendation? - SailNet Community
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post #1 of 19 Old 09-21-2009 Thread Starter
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Question Grinder / sander recommendation?

Well, I just finished watching my first haul out. The boat is on the cradle, and I had my first look at her hull. Yep, she's got blisters. With my month-early haul-out I have a perfect opportunity to get the blisters ground out and drying. Only problem is, what to use?

I have a nice (Porter Cable) random orbit sander, and a traditional (Makita) square plate palm sander. I even have a Dremel... However, I'm thinking that working a 27' hull-o-blisters probably warrants something that will work faster, right?

Can anyone recommend criteria / features to look for (rpm speeds? sizes? amps? Something else?). I can go down to Lowe's and roll the dice, but I'm hoping someone can give me something to go on. If you have one that you really like, and you think it was reasonably priced, please let me know

I was looking at a "PORTER-CABLE 4-1/2" 7.5-Amp Angle Grinder", but it looks like these have stone wheels... Don't I want to be using sandpaper discs? Do I have the totally wrong tool here?

Thanks,
Chris

CS27 #1254 ~ Ravat
PYC, Lake Ontario

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post #2 of 19 Old 09-21-2009
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Well Chris, I have just completed grinding all of the bad paint and gel-coat off of a 42 Tayana. I used Makita products. I used the mid sized makita grinder, It had plenty of power, and wasn't such a brute as a full size large grinder. For the sanding I use either a 5" random orbit variable speed for finishing, or the 5" regular random orbit for the bulk or coarser grits. The real magic is in the abrasives you will use. Regular sandpaper loads up, and doesn't cut very well, however some very ingenious individual came up with a sanding disk that is called a flap wheel. Mounted to your angle grinder, it is capable of removing anything, and I mean ANYTHING, with EASE! they are available in grits from 36, up to 120. These discs, even at 120 grit, could go through the most tenacious material, and show little signs of wear. They cost about $10 each, but the beauty is that you will probably only need 1. I used 2, I stripped off a total deck of cracked and crazed gelcoat, and the entire topsides of 2 part polyurethane, and primer. They are by far the best thing I have used on my rebuild. I will get you the MFG. name tomorrow. I have seen a similar product by WALTER ABRASIVES, but have not yet used one of theirs, because the ones I have won't wear out! One thing to keep in mind, is if you decide to grind the old away, do it with HORIZONTAL STROKES. that way when you go to trowel on your epoxy, you will have an easier time re-fairing it. Don't do it haphazardly.

Why, why, why?
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post #3 of 19 Old 09-22-2009
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Chris,
I like Milwaukee tools myself, but they're really all about the same. Any 4 1/2 inch grinder with those flap discs capnblu mentioned is a pretty good weapon of choice. The bigger the grit the better, I'd start with 36. You may want to check with where you're hauled out, some places require you to attach a vacuum to any sander or grinder to prevent any antifouling on the bottom from getting into the environment (that's how it is where I'm hauled out in CA). I bought a Festool sander for this purpose and attached it to my shopvac with a length of bilge hose. The sander was pricey but one of the best tools I've owned. Have fun!

Ed
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S&S Swan 43

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post #4 of 19 Old 09-22-2009 Thread Starter
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Yes, we need to put a tarp on the ground when we sand, and I think use of a vacuum is a good idea regardless of the rules, so I'd planned on it. That was one of the criteria I'm interested in - how well does the dust port on various models really collect dirt. Being a woodworker I've seen all kinds of variety in how well they work on other tools.

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post #5 of 19 Old 09-22-2009
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I use a 4" right angle grinder for jobs like that, really good at taking material off quickly.

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Get out there!

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post #6 of 19 Old 09-22-2009
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We are in a "Certified Clean Marina", I rented this from the marina when I did my bottom sanding job.

Combined with their vacuum attachment for fine particles, I found it ideal and not too heavy. After many many hours of sanding my arms still felt like there were going to fall off

Random Orbital Sanders - Festool

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post #7 of 19 Old 09-22-2009 Thread Starter
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As a follow up question, is an angle grinder interchangeable with a random orbit sander for blister removal? Or do I really want to use the angle grinder for initial blister removal, then the random orbit for when I'm fairing the repaired hull?

I see the use of "sander" and "grinder" mixed somewhat inconsistently in how-to articles, so it's hard to tell just what I need...

Thanks,
Chris

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post #8 of 19 Old 09-22-2009
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the angle grinder is the tool of choice, the random orbit is good for paint and fairing but way too slow for real removal of material.

another option for blister opening is a sand blaster in very talented hands, or even a soda blaster but its slower.
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post #9 of 19 Old 09-22-2009
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Quote:
Originally Posted by T37Chef View Post
We are in a "Certified Clean Marina", I rented this from the marina when I did my bottom sanding job.

Combined with their vacuum attachment for fine particles, I found it ideal and not too heavy. After many many hours of sanding my arms still felt like there were going to fall off

Random Orbital Sanders - Festool
I do a lot of sanding every year- Love my Festool.
It won't be as aggressive as aright angle grinder if you're grinding out blisters. But my 150 with a heavy grit takes down epoxy REALLY fast.
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post #10 of 19 Old 09-22-2009
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I just finished the job using a 6" random orbit Rigid sander. Worked great and was aggressive enough to get the job done without going through the hull. On our last boat, I used an angle grinder and will never do it again. The high RPM (22,000) is too much for fiberglass, IMHO. On the other hand, the 6" random orbit sander is quite aggressive, much more than a 5" grinder. The increase of only 1" diameter yields 44% more grinding area.

The Rigid had a silly dust bag that I took off. The good news is that it easily accepts the hose of a Shop Vac. I did the entire hull with the Rigid/ShopVac setup and had great results using 40/60/120 grit. You don't need to press hard.

To get all the paint off, you may not want to grind. We used 1" wood chisels to scrape it off, sharpening frequently. We also used carbide-tipped paint scrapers. When the paint was removed, I used the sander to smooth everything out. MUCH faster than sanding through many layers of paint. Also, the chisels/scraper gave us paint chips vs. paint dust. MUCH easier to collect!

Once I got to bare glass, I used an ice pick to gouge out the few blisters that I had. I would not grind since you will end up going too deep. I also recommend popping the blisters in the fall and filling them with epoxy in the spring. You'll need the winter for them to dry out.

Good luck.

Sabre 38 "Victoria"
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