Best Grinding Discs?

Discussion in 'Fiberglass and Composite Boat Building' started by LMB, Mar 19, 2011.

  1. LMB
    Joined: Nov 2008
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    Location: North Carolina

    LMB Junior Member

    Anybody found one type of grinding disc to be superior than another for big material removal jobs? I'm removing gel-coat from the deck of a work boat. Doesn't have to be pretty, just need to get down to the underlying mat quickly.
     
  2. Dean Smith

    Dean Smith Previous Member

    60 or 80 grit on an angle grinder 7 inch with backing pad, or try Rondella which is esp for aluminium but methinks would work
     
  3. LMB
    Joined: Nov 2008
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    Location: North Carolina

    LMB Junior Member

    Started with 7" 24 grit on grinder. Gel-coat is thick and it's a little slow. I sometimes use the flap style discs for smaller areas on a 4.5" grinder which generally work pretty good but I didn't have any larger ones in a courser grit. I figure some materials or brands might last longer as well. All are fairly pricy so I want to stock up on the right thing.
     
  4. CatBuilder

    CatBuilder Previous Member

    I use 35 or 40 grit on a 7" polisher/buffer. I just use the crap at Home Depot or Lowes. They last forever and tear right through fiberglass like it's butter.

    They really don't lose their bite very quickly at all.
     
  5. iceboater
    Joined: Jan 2011
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    Location: Iceland

    iceboater Junior Member

    I use 5" inch diamond segment grinding disc. It lasts forever, but you have to be careful to keep the disc moving or it will grind in very fast.
     
    BrissoDamo and CDK like this.
  6. Landlubber
    Joined: Jun 2007
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    Location: Brisbane

    Landlubber Senior Member

    "I use 35 or 40 grit on a 7" polisher/buffer."...yep, works for me too...soft backed pad, varieble speed AEG electronic unit and it rips it off and basically never blocks up, you can go coarser too if you like.
     
  7. CatBuilder

    CatBuilder Previous Member

    Same setup here. Variable speed is the key. I use a rubber back pad, which is less forgiving, but I got very artistic with it after doing hundreds of scarf joints with this tool for my failed wood/epoxy hull. :D

    I have a confession to make: I really enjoy this tool. It is my favorite in the entire shop. I even use it to cut peel ply off fiberglass edges! ha ha ha

    Only complaint? I filled my entire shop (and several meters outside the shop) with fiberglass dust today taking the overhanging glass off my hull that is nearing time to pull from the mold. Now, it's a very itchy place.:eek:
     
  8. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    A polish/buffer type of grinder with a 7", 9", 10" or the rare 12" pad is the fast material removal tool. If you're serious about material removal, then it's all about the grit and speed. 16 grit on my 10" will eat through most anything in very short order. The 10" is a beast and not easily used in confined spaces, plus it has so much torque, you have to use both hands. 24 or 36 grit on the 7" are the usual choices. They cut aggressively, but with a lot more control on the 7". 40 and up grit is for sissies. Do yourself a big favor and learn how to fabricate a hood for this tool and plug the shop vac hose into it.
     
  9. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    And step up to an actual grinder, 5000 RPM and heavy, it will have a great deal more power than a buffer/sander.

    Check your local abrasive supplier if you want better discs, they will a few grades to choose from.
     
  10. Landlubber
    Joined: Jun 2007
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    Location: Brisbane

    Landlubber Senior Member

    "it will have a great deal more power than a buffer/sander."....wrong mate, the AEG is UNSTOPABLE cos it is electronically controlled, it runs same speed no matter how hard you can shove it. Mine is about 10 years old now, has a little light that is supposed to show overload, never seen it on mate. It is a supurb tool.
     
  11. War Whoop
    Joined: Jun 2003
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    Location: Sunny Ft Lauderdale Fla

    War Whoop Senior Member

    Peeling gelcoat?? I use a makita planer, the carbide knives are cheap and reversible,Cleanup and tight areas with a 4" grinder.
     
  12. Frosty

    Frosty Previous Member

    Do you want to play with it or get the job done,--- 16 grit on a 10inch.

    If your ripping anti fouling off as well 60 70 is usless.

    Value for money ---Bosch.
     
  13. michael pierzga
    Joined: Dec 2008
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    Location: spain

    michael pierzga Senior Member


    Power planer does a good job. If its a big job with resonably flat surfaces..

    Also consider renting a concrete planner or a PPT.

    http://www.novatekco.com/html/ppt.html

    http://www.makita.com/en-us/Modules/Tools/ToolDetails.aspx?ID=316444
     
  14. Wynand N
    Joined: Oct 2004
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    Location: South Africa

    Wynand N Retired Steelboatbuilder

    use a buffer/sander type grinder with 60 /80# Abramat discs. Ones with velcro at the back. If clogged up, take it off, knock out the dirt until see through again and go again.
     

  15. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    Iceboater in post #5 offers the best solution. You can do the whole boat without changing discs and you don't get tired because there is hardly any pressure required. All you need is someone to wipe the dust away and a long shower afterwards.
     
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