Best Grinding Discs?

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

  1. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

  2. Frosty

    Frosty Previous Member

    Have I got this right --your ripping off gel coat and antiflouling for osmosis treatment with 60 grit ? Come on guys --60 70 grit, I do my toes nails with that.

    What do you get 10 seconds a pad, no wait 5 seconds.

    What do you think they make 16 grit for?
     
  3. CatBuilder

    CatBuilder Previous Member

    A real man uses two grit! You're all a bunch of sissies! ;)
     
  4. LMB
    Joined: Nov 2008
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    LMB Junior Member

    I appreciate the input and can relate to most responses. For moderate material removal and prep a disc sander with 36 grit on a soft back up pad has worked well. For rough stuff that might tear up a pad I usually use the 24 grit flap discs on a 4.5" grinder. Neither of those are cutting it for this job. I tried the somewhat standard 7" 24 grit on a 5000 rpm grinder and was not overly impressed either. The 16 grit was not readily available but I may special order. I'd also like to try the 7" flap wheel in a 16 or 24 grit to see how it compares. Those Zec wheels look real interesting too. Similar to the flap wheels which have worked well for me.

    I'm also going to try a dust collection shroud. Product called the dust muzzle is cheap enough and looks like it might work. I'm open to suggestions here. Not my first rodeo but I'm always looking a better way.
     
  5. Frosty

    Frosty Previous Member

    2 grit might work, but if you really want to get on with the job tie 2 house bricks on some 6mm steel wire on a good 110 V drill.

    The dust is a problem,-- If I had air drills I would use 16 grit and have the wife stand by with a hose pipe.

    16 grit wont clog,--well like 60 would, a 16 will last a long time.

    I recently had a cock up with a job joining a dinghy to make it smaller . The resin did not go fully off,-- I guess the hardener was old or something. I didnt have time to mess about. The 16 grit ripped off a 2 meter by 4 inch strip of soft resin and glass in minutes. I used but 1 16 disc and it is still usable. On the floor was a bunches of cotton wool like mush.
     
  6. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    I had a crew of 6 guys that would grind for 8 to 10 hours a day, we used 16, 24 and 36 grit on big grinders (5000 RPM), finer grit than that and we would drop down to a lower RPM. We used several different brands of grinders, each had a purpose.

    At the time the diamond discs weren't as easy to get and cost far more than they do now. If you want the surface to be smooth it may be difficult for less experienced person to do it with a stiff diamond wheel.

    A 4.5" is OK for small stuff, but won't cut it for high speed removal of material.

    There is huge difference between a polisher/buffer and a high speed grinder, even if its an electronically speed controlled model. We burned of several models of these when guys would use them in place of the big grinders, they would use them because they are lighter and easier to hold in difficult positions.

    Flapper discs are a waist of time because you are always grinding with worn out grit, rookies like them because they are easier to control and remove material slower. If the backing wore away quicker it would expose fresh grit faster and speed things up.

    How big of an area are you working on?
     
  7. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    Believe me, the ZEC discs will leave a flap disc behind in a cloud of dust, last like 10-20 times as long as an ordinary disc & cut well until worn right out. Regards from Jeff.
     
    Last edited: Mar 21, 2011
  8. CatBuilder

    CatBuilder Previous Member

    Lmb: thanks for the tip about the dust hood. Will get one of those before my next grinding job.
     
  9. Steve W
    Joined: Jul 2004
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    Steve W Senior Member

    Agree, those zec discs are the ****, 16 or 24 grit work best,i actually prefer the 24grit. You can make your own dust shroud out of fiberglass which is what we did 20yrs ago when you couldnt buy them,we screw on one of those bristle type door sweeps to the bottom, i buy them at home depot and cut to length,when we first made the shroud we actually used a seal on the bottom edge and drilled a series of holes in the shroud that we could tape over to adjust the vacuum so that with it on a milwaukee grinder we could grind a hull bottom with the vacuum supporting the weight of the tool. We have just recently bought some metabo shrouds for 4 1/2" and 9" grinders which are made of urethane so are flexible, we bought one of those clear lexan ones too but decided upon looking at it that its too wimpy for shop use,probably fine for home handyman use.
    Steve.
     
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  10. michael pierzga
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    michael pierzga Senior Member

  11. LMB
    Joined: Nov 2008
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    LMB Junior Member

    All great input. I ordered a 16 grit Zec this morning. Based on responses I may go ahead and order a few more. ondarvr, you definitely get where I'm coming from. When grinding I routinely change tools, discs, grits and RPMs to fit the task. The current job is really not so big - but it has caused me to look for a more efficient system. Just a 17 foot skiff with maybe 100 square feet of sole to be stipped down to the mat. Sounds easy enough but there is probably 1/16" of gel-coat on this thing ( part of the problem). After about 3 hours of grinding we've stipped maybe 15 square feet. That's using a 7" 24 grit on a 5000RPM grinder. I'm a patient guy - but not that paitent.

    Also, I've been post-poning dust collection for a while but its at the fore front again. Between the health risks, the mess and lost time cleaning up I've got to employ a better system. I'm a small tight budget operation but I think I'm onto some cost effective solutions. Thanks michael for the link to the dustie. Their line of products is the kind of stuff I'm looking. Call me a sissy, but I'm looking the cleanest, safest, most efficient tools and processes, that I can afford to use.
     
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  12. Frosty

    Frosty Previous Member

    Im interested in the dustbag. I have a rotten little job on the bathroom window.

    Do you get in the bag or do you work outside it--if you do how do you see or work the grinder.

    I was thinking of taping a black bin liner round it but got no further.
     
  13. mark775

    mark775 Guest

    Yes, Zeks take off some material but listen to Par on this one. Course grit, large disc, more control (larger area in contact at one time) with larger diameter for more even finish. I am happy leaning on a nine inch Milwaukee. You're gonna end up with a comparatively choppy surface with the Zek.
     
  14. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    Sounds like you've got it sorted, typically when I've ground out a cockpit sole say for a 40' game boat say 10' x 10' / 9-10m2 prepping for an overlay decking, including tenting & clean up would be about 4 hours.
    As Mark alludes to using a large "footprint" does the job most evenly on the job, I see plenty of people driving sanders around on the edge of the disc only & "chopping" up the surface, try & tell em, some listen, some.........
    With your 7" sander/polisher an 8" soft pad set up for velcro discs is a handy addition too.
    Regards from Jeff.
     
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  15. tunnels

    tunnels Previous Member

    Have found over the years the really coarse disc's are not nessasrily the quickest or best . If the disc is just glogging up Take them off and drop them in acetone ! the grap just falls off revealling an almost unused disc . :D
    let them dry before you refit to the grinder . The saving on discs can off set the price a litre of acetone . :p
     
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