Best tool for grinding fiberglass?

[Roger Long]

Say, what is the best tool for major sculpting such as the scarf bevel on old thru hull hole patching? I'm using a flexible mesh grinding / cutting wheel that works great for surface grinding but it's slow and turning out to be difficult to make a smooth recess with.

 

[sailingdog]

I use a random orbital sander with a 60 grit disc on it. An angle grinder would probably work quite well too, but I prefer the control I get with the random orbital sander.

 

[William12213]

I would say it depends a lot on how big the area is and what you comfort level is with a tool. If i am working on a big area I use a large body gringer with a sanding pad. when there is a lot of material to remove it does it fast and level. I do normally finish it off with a orbital for a very smooth finish.

 

[Ross]

I did a lot of work with a 25 grit sanding disk on a right angle grinder. I left the surface with that finish when I started the glass work. My bonds were excellant. I installed tie down hard points by grinding the woven roving flat and glassing down a forged bronze loop. I used 1/4 inch silicon bronze welding rod and bent it to the shape I wanted and just glassed the ends down. They distort before they pull loose.

 

[RichH]

Variable speed, small angle-grinder with 40 grit. Then rotary rasp mounted in electric drill to do the 'finishing' of the bevel.

 

[Ross]

If there is very much material to remove then it is worth while to use large and powerful tools. The details can be finished with finer tools. I didn't work very long on my boat before I up-graded to industrial quality tools.

 

[sailaway78]

Angle grinder

I got a 7" sanding disc attahment for my 4 %1/2 inch angle grinder at Home Depot. With 50 grit discs, this will remove a lot of material pretty quick. You will need to follow it up with and orbital or something similar for a final pass to smooth it out a little bit.

 

[Ross]

Re: Angle grinder

Just don't start a conversation while you are holding those grinders. They do a lot of work very quickly.

 

[Hermit Scott]

I have found the answer to this one! Twisted wire wheels will allow you to take as much material off as you like quickly. They do not fill up like sand paper, they throw the material out. I used a 4-1/2" grinder and a steel, twisted into braids, wire wheel.
This also works great if there is bottom paint that keeps clogging your sand paper. My boat had 4" diameter blisters, I can remove one in 2 minutes. Also it leaves the surface perfect for adhesion with new glass.

 

[Franklin]

I have three attachments for my 110 volt drill

1) wire wheel
2) small grinding wheels
3) very pourus grinding wheel

I got all three at Home Depot. I tried #3 first and it worked so great, I never tried #1. I used #2 for the small cracks where #3 couldn't get to. #3 didn't clog but it did get eaten up with doing 3 small projects.

 

[Hermit Scott]

If I was going to do a large area, I would try a 7" grinder with a braided wire wheel. Like Ross said though, both hands on that things. When your fingers go into the grinding wheel when you are trying to adjust the gaurd before shutting off the grinder, you could miss a few hours of work talking to an ER doctor who just might say "the flesh is gone! what do you want me to sew together?"
The rule is now, if the grinder is running I always have both hands on the handles.

 

[Ross]

My concern with a wire wheel is the very thin layer of carbon steel that get rubbed onto the substrate you are cleaning.

 

[caguy]

For your purpose have you considered a rotary file? I used one the other day to open up a hole. I have also uses mill cutters with a high speed drill mptor.
For convex contures I use a 3'' wide belt sander. It takes the material down quickly and with a finer grit leaves a nice finish. It picks up the shape of the surrounding area nicely. I will then finish with an orbital sander. I have tried large disk but inevitably end up gouging the work.
That wire brush thing sounds interesting hermit. Do you have a picture you can post?

 

[kendall]

I use the 'flat' flap type sanding isks on a small grinder.
You can get them in various sizes and grits you can select one agressive enough to make the job go quickly, but not so coarse that you'll tear holes in the boat.

Also seem to last much longer than other sanding disks

Ken.

 

[Ross]

If the glass where Roger is going to work is a half inch thick he will be opening a tapered area as big as a dinner plate. A half inch deep at the hole and almost no material removed at the outer edges. That is an average of a quarter inch thick 12 inch round piece of fiber glass that will be reduced to dust. It can't be done efficiently with hobby tools. It is near the bow of the boat so it must be done with great care because it will be subject to impact with flotsom and possibly with ice.

 

[mudtertel]

I never thought of a wire wheel would you use a cup or a round. I have a bottom job , the keel which is steel and the hull which is fiberglass. I was going to use Epiglass . then I was going to use Interlux two part bottom paint 2000e. I got three gallons for a 25.5 Hunter. What do you think? Any comments will help.
Thanks, Mike

 

[Hermit Scott]

One of the pics shows a braided wire wheel that I put a bolt through to use on a drill to hit a different angle, it has been used alot so it's a little unbraided. The other is still pretty new as you can see the braids are still together, it threads onto a 4-1/2" grinder. The other is a flap disc sander, my favorite metal working tool in the world. As kendall points out they remove alot of material fast.
In fact in another post I show a pic of a through hull in a c30 for the sink. I cut away part of the wet muffler base installed by the factory. It is 3/4" plywood on top of about 2" of resin with no fiber in it. I chiseled away the wood and then just used it to eat away 2" of resin in a few minutes. There was no paint so I wasn't worried about it getting clogged up. Otherwise I would use the wire wheel.

 

[sailingdog]

You are aware that Interlux Interprotect 2000E is a barrier coating, not a bottom paint, and you still have to apply a bottom paint to it to prevent barnacles and such from attaching themselves, right??

I never thought of a wire wheel would you use a cup or a round. I have a bottom job , the keel which is steel and the hull which is fiberglass. I was going to use Epiglass . then I was going to use Interlux two part bottom paint 2000e. I got three gallons for a 25.5 Hunter. What do you think? Any comments will help.
Thanks, Mike

 

[Prime Time]

Love that grinder

I agree with Ross. Angle grinder with a coarse sanding disc. That combination never ceases to amaze me with what you can do with it. I used mine intensively when doing my bottom job.

 

[jibes138]

Too much speed

I used an angle grinder on a hull repair but found it removed material too fast and was difficult to control. I then switched to a regular variable speed drill with a rubber sanding disc and adhesive backed sandpaper disks. The flexible rubber allows it to form to the surface and it removes material amazingly fast and very controllable with the slower speed. Angle grinders are high RPM for grinding wheels, they work great with a diamond wheel for cutting special shapes on ceramic tile. For the large radius bevel I think the sanding disk would be ideal and less chance of a screw up if it slips.