Diamond blades for composites

Discussion in 'Fiberglass and Composite Boat Building' started by Steve W, Feb 9, 2014.

  1. Steve W
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    Steve W Senior Member

    Looking for recommendations for a circular saw blade for cutting 1/4" or thicker fiberglass, I have a Crain undercut saw that uses a depressed center carbide blade meant for door jambs and while its the perfect tool for the job I have to do the blade will not go the distance. Im wondering if anyone has experience with the diamond grit blades which you can buy anywhere now for cutting concrete, marble etc. They come in solid rim and segmented types, any idea which would work best?

    Steve.
     
  2. kapnD
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    kapnD Senior Member

    I like to use abrasive blades on composites, they wear out more quickly than diamonds, but are appropriately priced and make a very clean cut. The diamond blades i've tried are pretty slow cutting, and will get too hot if they are pushed. They thrive on water feed to cool the blade and carry away debris, not necessarily a good thing for your laminates.
    Carbide blades are dangerous to use on anything other than wood or soft products, unless they are specifically designed for that use. The carbide tips can fly off, creating dangerous hot projectiles!
     
  3. PAR
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    PAR Yacht Designer/Builder

    I use diamond blades all the time, they're about the best thing going. Abrasive blades just get eaten up quickly and create more dust. The smooth edge blades make a cleaner cut for more precise work, while the notched edge blades are more aggressive.

    They're available in the usual sizes: 4", 5" 7" and 10" are most common. A 4" in an angle grinder can do some serious work. They also make offset blades for flush cuts.
     
  4. Steve W
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    Steve W Senior Member

    Yeah, ive used abrasive blades mostly but now that the diamond blades are available at a decent price I thought id give them a try. Paul, any ones you like more than others,are the ones from home depot or northern tool ok.

    Steve.
     
  5. PAR
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    PAR Yacht Designer/Builder

    Northern Tool and Harbor Freight blades are the worst. It boils down the to quality of the particulates and resin used to get the grit attached to the the blade. The same deal as with sand paper, you'll get what you pay for generally. Simply put, try a comparison between Harbor Freight 40 grit and a nice 3M sheet and see which holds up longer. I've found diamond blades pay for themselves, while abrasive blades don't. You can clean a diamond blade and keep going while an abrasive is just worn down.

    If you get "into" these blades, there are lots of choices, mostly arranged around intended use, cutting conditions (wet and/or dry) and most importantly the actual material used for the abrasive. The best are natural diamond, but a 4" disk will cost $150 bucks, which is hard to take. Cubic zirconia steps up as a very close second and the cheapest ones (4") will be about $10 = $12 bucks. These will easily outlast any of several abrasive disks, but their weakness is you can't get them hot. I use a weeping hose, like that used to water garden plants. You need just enough water to cool the blade, but not so much to make a mess. It also dramatically controls dust too. The better blades are also on thicker and more heat stable disks, so they hold up better if used dry.
     
  6. redreuben
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    redreuben redreuben

    Pretty much what Par said, "proper" diamond blades are worth the money if you are going to use them a lot, however for a little work "hardware chain " blades from the tiling section are just fine.
    My only suggestion is use a 5" blade if you have the tool for it, particularly for straight cuts, 4" blades are much harder to control by comparison.
    I use them in an angle grinder for versatility.
    As for using water, wouldn't go there ! But our domestic supply is 240 V !
    Air tools no problem !
     
  7. PAR
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    PAR Yacht Designer/Builder

    A good grinder and common sense can make wet cutting possible, though I do take for granted my air tools. When I say wet, it's not like a typical tile saw and spewing water everywhere, but just a light mist or spray, much like that coming from a spray bottle (which I use sometimes), to knock down dust and keep the blade cool. It's also fairly easy to tape off areas with some plastic sheeting, so water run off goes where you want.
     
  8. Steve W
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    Steve W Senior Member

    Yes, it goes without saying that the cheap ones are not going to be as good but all I need is good enough, hopefully better than the abrasive ones. The tool I want to use it on is a Crain undercut saw which is really a modified angle grinder which allows for flush cutting to the surface, its the perfect tool for the job I have to do and uses a 5 1/2" blade x 7/8" arbor, I have about 36ft of 1/4" thick glass to cut and don't want to use a freehand tool, this tool with the right blade will give a machined like cut with little fairing of the edge.

    Steve.
     
  9. SukiSolo
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    SukiSolo Senior Member

    For smaller cuts the Fein Multitool has some diamond blades for cutting composites. Brilliant little tool for flush cutting, trimming, sanding, bevelling etc. It has saved me lots of hassle on dinghy, small keel boats and small outboard boats (Dell Quay Dorys for example) glass repair work.
     
  10. Steve W
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    Steve W Senior Member

    Yes, I have a fein and its great for a lot of things but is nowhere near up to the task of what I need to do, the crain saw also cuts flush which is great for a lot of bigger jobs. I don't need the flush cutting feature for this project as I will be blocking it up to cut 4" above the surface so don't need the depressed center blade.

    Steve.
     
  11. PAR
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    PAR Yacht Designer/Builder

    A cheap, Lowe's/Depot 5" diamond blade will easily get 36' done for you Steve. Most will have the diamond knock out for the 7/8" arbor adapter. If not, this is a commonly available piece (a few bucks too). Once you go diamond, you'll never go back to an abrasive blade.
     

  12. Steve W
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    Steve W Senior Member

    Thanks Par, that's what I was after, ill give it a try.

    Steve.
     
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