Saw blades

Also crossposted to rec.crafts.metalworking
Installing Hardie Plank siding. (Fiber cement combination) Manufacture states that I should use a special blade. Went to Home Depot, and yes, they make a special blade. It is simply a carbide tooth blade with with a total of 6 teeth. 7-1/4 inch diameter.
Can somebody explaing why a six tooth carbide blade would cut any better than, say, a 24 or 40 tooth blade that I use for lumber? I don't understand the physics.
Thanks,
Ivan Vegvary
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The "special" blade is usually a diamond blade. The crew that did my house had a set of them. When I did the shed, I just used an old carbide, it worked OK but wore down *very* fast (we threw it out at the end of the job). Same with jigsaw blades. They work, but they last about ten minutes each.
Are you sure the blade you got was carbide, and not diamond? Diamond is common in masonary blades.
As for the teeth, remember you're not cutting wood. You aren't going to get a smooth surface, so "more teeth" is useless. As long as you have *enough* teeth, it works, and you certainly don't want to be making a fine dust of that stuff - coarse dust is better. If you have too many teeth, it acts more like a grinder and less like a cutter - and if it's a grinder, it'll be the hardie plank grinding the saw blade, not the other way around.
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http://www.coastaltool.com/cgi-bin/SoftCart.exe/a/hitachi/hardiplank_blades.htm?E+coastest
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I do not know that a 6 tooth would work better than a 24 tooth blade except for the fact that there will be better chip clearance with fewer teeth. Sorta like a single flute router bit cutting better than a double flute bit. That said, I have had moderate experience with cutting fiber cement siding and for my first project of residing the side of my home I used a 24 tooth circle saw blade. The results tend to be rough and jagged. For about $15-20 dollars I bought a diamond coated blade for cutting ceramic tile and masonry products and had very food results. These have no teeth other than the abrasive edge.
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Physics of the blades aside, I suggest looking at shears instead... The dust is brutal from the saws and the shears make none. The silica has to potential to kill you in the long run if you breath it in... I wore a mask and used a diamond blade in an angle grinder to cut the fiber cement trim on my house but the siding was done with the shears.
Porter Cable 6605 Hardiplank Fiber Cement Siding Shear DEWALT D28605 Heavy-Duty 1/2-Inch Variable Speed Cement Shear
I've got the PC shears and they work fine.
John
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wrote:
SNIP

potential to kill you in the long >run if you breath it in... I wore a mask and used a >diamond blade in an angle grinder to cut the fiber >cement trim on

No kidding. After buying a garden full of landscaping (my drifting cementitious dust was floating one way all day onto a neighbor of my client) and then later replacing the grass and dirt near the area we were using on the driveway to cut, and still later to have to buy 3 car washes....
I ONLY use shears for cementitious fiberboard siding. By the time you cut a long gable piece on a low slope with that saw they will think you are signalling them on the space station. The amount of dust is unbelievable, and in a residential neighborhood, completely unacceptable. Never again.
Robert
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So Robert, how smooth of a cut do those shears make. The first time I saw them a several years ago I could not possibly see how they would work, decently. Do they actually leave a smooth cut?
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They make a perfectly acceptable cut if you use them correctly... which means keeping the anvil side of the jaws flat on the siding. Failing to use them properly will result in a ragged edge. The learning curve is real short... if you pay attention to what you're doing!
John
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They are much improved from the ones we had many years ago. I have had the PC shears now for a few years and have cut Hardie plank, Duraplank and Maxiplank as needed. It works great on all of them and if you use them correctly the shear will roll up a coil of material in front of the shears and throw out a few chips. That's it. Cutting on a driveway it is easy to clean up with just a broom. And it cuts fast, too.
When you cut a long piece for under a gable (say in a 5/12 or 4/12 roof) it will easily handle the 3'+ cut on the long cuts up at the soffit or rake. With a little practice you can use them as a nibbler around pipes, and can even cut (large) crescents.
Make sure the two sides that ride on the siding or sitting dead flat on the siding when you are cutting though, or you can chip up the edges. It isn't as smooth as a saw cut, but who sees the end cuts under window or corner trims anyway? Applied properly, all of these products are applied so that any exposed ends are factory made, so all your cuts are covered.
On the next cement plank job, buy it, you'll love it! Any of my contractor buddies I have lent it to have gone out and immediately bought their own. That says a lot there as most would rather borrow...
Robert
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Thank you sir!
wrote:

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wrote:

I have to agree with the guys recommending the shears. You can rent some or buy a set and sell them on Ebay when your finished with your project. If you have your supplier give you the safety sheet you'll find all kinds of ugly stuff on there about breathing the dust. When these products first became available here, all the siding guys tried to use saws for cutting it but nowadays all the pros use shears.
Mike O.
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I've found the dust to be somewhat more manageable using my 18v Makita with an old carbide blade. Fewer rpms, somewhat less dust but a dust mask still a necessity. That said, if I were doing a whole house now I'd spring for the shears.
--
Dave in Houston



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I used Hardie Plank siding on my house and cut it with an old B&D circular saw with a diamond tipped masonary blade from HD. The saw was toast after this job- bearings were shot because of all the dust. If I was going to do it again (hopefully never) I would buy the shears. I bought a PC coil framing nailer just for the job and it worked like a champ. I was going to sell it again the job but because I liked it so much I decided to keep it to do fencing projects. I can't believe my neighbors didn't complain what with the dust clouds I was sending up cutting the fiber cement siding with a circular saw. Ripping a 12 foot length was a joy. To cut out small notches I used my 4" angle grinder with a diamond blade and for holes I used a Rotozip with a tile cutting carbide bit. I learned that on the ends it was necessary to pre-drill and hand nail. I'm very happy with the Hardie siding.

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