Grinder Question

[lucid484]

Maybe you can help out oops.....

Got my splash well cut out with a sawzall the other day and now i'm going to cut away the remaining fiberglass on the transon and about 12"'s of the already rotted stringers and then sand down evenly the inside of the outter skin.

question is what would be the best type of 4" grinding pad to cut the fiberglass and stringers away and they what would be the best type to smooth out the surfaces?

I think you once said a flapper or something is good?

 

[Bob_VT]

Re: Grinder Question

Flapdisc ....one you use one ....you will understand

 

[drewpster]

Re: Grinder Question

Agreed....36 grit flapper. Affords great control and allows you to get things flat. They also last a long time. Some like a backing pad and a sanding disc. They tend to dig in and are too aggressive in my opinion. I have used both, but I use flappers when I need more control.
I have a large grinder with a sanding pad when i have to remove allot of material. I use the 4" for all the other rough grinding.

 

[JAFO1]

Re: Grinder Question

For cutting fiberglass in areas where I didn't want to get into the hull, stringer bottoms and side tabs, I used an abrasive cut off disk. I tried one made for masonry and one for metal. The masonry cut off wheel, not a grinding wheel, is a little thicker than the metal disk and worked better for me.
For sanding, I tried both solid (non flapper) and flap wheel. As said above, the solid disk grabs and bites and is harder, for me, to control. Flap disks are very manageable.

 

[ondarvr]

Re: Grinder Question

I actually dislike the flapper discs, they work, but when I'm grinding I want it to be fast and aggressive, single discs do this much better. After many years of grinding, sometimes for weeks on end, by that I mean pick up the grinder in the morning and stop only to changes discs for about 10 hours per day. What I found was that flapper discs are much slower, which depending on what you're doing may be a good or bad thing. I also use the metal or masonry wheels, they work well for cutting and grinding. Diamond wheels and discs can work well too, they can cut a smooth straight line. I also use a circular saw with a carbide blade, its very fast but leaves a crude cut. I DO NOT RECOMMEND THIS METHOD THOUGH, the carbide tips can come loose and fly very fast and far.

I have stacks of grinders, different grit discs, different types of backing pads, wheels, blades, tools, some air, some electric and they each have there own special purpose that no other tool works as well at.

If I had only a couple of choices it would be a grinder with a backing pad and disc, plus a solid wheel. This covers most jobs and works well.

 

[kemp]

Re: Grinder Question

I found the Blackstone ceramic 40 grit disc to be fast and aggressive, even more so than the zirconian type.

 

[bob1340]

Re: Grinder Question

I just removed what seemed like 27,000 lbs of old resin off of my 12' Gamefisher. I used a 5"/50 grit hook and loop disc on a 4.5" DeWalt grinder. This works very well for a job like this. I use lots of flapper discs on metal, but never tried one on glass. I will need to give that a go.

 

[oops!]

Re: Grinder Question

a rubber backing pad (this is sometimes called a flapper) with a 26 grit pad.
don't get the plastic pad

it makes short work of grinding.....

(i really pity ondarvr for the long grinding periods. i have my go rounds....but nothing like what he is talking about )

there is a flapper with many sheets of paper overlapping each other.....it works good.

remember....you are just getting rid of the old surface......a "rough and scuff". it is a common thing for home boat builders to go too far, and spend far too long grinding......but...it is a nessary evil.

please see the safety basics of grinding and glassing in the sticky at the top of this forum.

cheers
oops

 

[ondarvr]

Re: Grinder Question

The flappers I'm talking about are the ones with overlapping sheets.

I don't like them because on the ones I've used the paper doesn't wear away fast enough to expose fresh grit. The dull worn grit grinds down the surface slower and I don't want to be grinding any longer than I need to. The slower grinding can be OK if you're not comfortable or familiar with it, and sometimes if you're trying to shape a radius the slower speed is fine.

 

[redfury]

Re: Grinder Question

The flappers I'm talking about are the ones with overlapping sheets.

I don't like them because on the ones I've used the paper doesn't wear away fast enough to expose fresh grit. The dull worn grit grinds down the surface slower and I don't want to be grinding any longer than I need to. The slower grinding can be OK if you're not comfortable or familiar with it, and sometimes if you're trying to shape a radius the slower speed is fine.

This much I will agree wholeheartedly about. I used a few of them on my boat, thinking that I had used the previous one up. Nope, they just lose their aggressiveness and tame down after a few minutes of use due to this very fact.

I use some very heavy paper sanding discs for the 4 1/2 grinder on a hard plastic backing that are held in by the arbor nut. This works the same way as our edgers do for hardwood floor sanding at work..something I am familiar with. I found that I like this personally, and it really is quite aggressive. Wish I had used them earlier in my grind. They are no good though when you get into tight spots, the flapper is much nicer for inside curves or for when you need to "bump" the edge as they won't cut into the side glass nearly as easily as a disc will.

The discs are cheap as individual papers go, and they last because they are not hook and loop and paper...more like treated hardboard. The flappers are more expensive per, but you will get a long life out of them if you have the endurance to grind more slowly and methodically. I spent a small fortune on them because I thought they were wearing out too fast...now I have a few flappers I can use on other projects

 

[lucid484]

Re: Grinder Question

Thanks for the advice guys...Went to home Depot today ad heading to teh boat tomorrow to grind out the last of the transom! Heres what I bought.

-Dewalt 4.5" Heavy Duty 10amp 11,000 rpm Angle Grinder
-Comes with a metal grinding wheel but I also bought these
Masonry Grinding Wheel (it was only 3 bucks)
Cut Off Blade
60 grit Flap Disc (what was most recommended)
-Full body coverall with hood
-Safety Goggles
-Gloves
-MSA Multi Purpose Respirator (says its good for Paint,Chemicals,Asbestos, and fiberglass.

Think I should be all set and now I can finally get my hull cleaned up and soon hopefully start the rebuilding process!

 

[bob1340]

Re: Grinder Question

That's the grinder I have. Great little tool. It would be best to have 2 of them as they can get real hot real quick. If you have an air compressor make sure and blow the grinder out once in a while as it will be full of that Satan baby powder. I had 2 of the DeWalts at one time, but one of them finally went haywire. I do a lot of welding and such and having 2 grinders makes pretty good sense.

I don't have the full paper suit as I am 6'6" and 300 lbs! I do cover up well, but you will have that dang Satan baby powder dust everywhere and it will get into everything. Terrible stuff.

 

[Yacht Dr.]

Re: Grinder Question

Hello m8..

24 grit is the best for fiberglass bonds..

You have to remove ALL the Painted/gelled surface to bare glass if you want to bond glass on glass..

Please dont scuff gel to bond glass.. That bond will fail..

YD.

PS. The "flap" disk is inefficiant for serious grinding .. go get some 24-36 grit locks ( 3m ) save you time in our grinding suits to change..

http://www.acehardwareoutlet.com/ProductDetails.aspx?SKU=1000018131

It seems this site is out of them .. but this quick change is sweet.. look for the backing pad and suppliers for the disk ( not hub tightened with a nut ).

 

[tdrudd87]

Re: Grinder Question

I got real partial to this puppy when I was grinding mine down. Took a few months of grinding before it even started to load up with anything, and stil cuts great to this day. Dirt cheap too, for how long it lasted.

I only used flappers to smooth the surface of the high spots once this was done. It is very aggressive. 24gr carbide

Item 66613

Terry

 

[Yacht Dr.]

Re: Grinder Question

And when you start grinding on some softer/clogger glass .. just put these puppies in a small bucket of acetone..

You can use this trick with acetone on some of the disks.. get them un-clogged with an Acetone bucket..

YD.

 

[lucid484]

Re: Grinder Question

Hello m8..

24 grit is the best for fiberglass bonds..

You have to remove ALL the Painted/gelled surface to bare glass if you want to bond glass on glass..

Please dont scuff gel to bond glass.. That bond will fail..

YD.

PS. The "flap" disk is inefficiant for serious grinding .. go get some 24-36 grit locks ( 3m ) save you time in our grinding suits to change..

http://www.acehardwareoutlet.com/ProductDetails.aspx?SKU=1000018131

It seems this site is out of them .. but this quick change is sweet.. look for the backing pad and suppliers for the disk ( not hub tightened with a nut ).

? YachtDr when would I try to lay glass over gelcoat? right now the innerskin on my transon is just falling apart..some of it i was able to break with my hands and the wood in whats left is all mush....i just want to cut out the last bit of perimeter glass on the transom and scuff up the outer shell.

my little dremel with 1" fiberglass cutting wheel was actually cutting alot of the inner skin....it was just taking a while with such a small tool.....but once its cleaned up and scuffed my play is to bond the new plywood to the outer shell with PL like alot of people have. 1 difference beinge the mid lower section on the transom where the outboard attached actually sticks 1" out of teh boat...so i migth make a plywood cutout and glass that in so the rest of the transom wood can go flush over it.

here's a link to my original thread with some newer pics...i'm going to be deleting it and start a proper thread that makes sence...and i'll get more pics tomorrow so I can get some more guidance.

look at the 2 newer pics I posted when i cut the splashwell out last week and you'll see what I mean.

http://forums.iboats.com/showthread.php?t=282923&page=3&highlight=lucid484