hole saws for fibrous cement sheet?

Fibro cement sheet (the stuff that replaced asbestos) seems to be tough. I needed to make some ventilation holes, and got out my hole saw (intended for wood). It made two 67 mm holes but the third took ages. The teeth were blunt as a budgerigar's bum afterwards. So I bought another hole saw, the cheapest I could find, but that only did one hole and the teeth were gone. So I wonder: are there hole saws made for masonry? I have not seen such item at local hardware emporium.
P.S. I did use a dust mask and ensure others were away while attacking this fibro shit.
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They must be available. Had one years ago (4 inch) for cutting through brick veneer house walls to install dryer vents. Google for them. WW

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Just dont try to find it at any major hardware stores, theyre too stupid to even know what it is.
http://www.google.com/images?hl=en&biw=1020&bih=596&gbv=2&tbs=isch%3A1&sa=1&q=diamond+hole+saw&aq=0&aqi=g1&aql=&oq=diamond+hole+s
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On Sun, 16 Jan 2011 05:19:42 +0100 (CET), Anonymous

Yes, they have a grit for the cutting edge. I have one. I think it's carbide. They may even make diamond blades but that will be costly. I cut thru ceramic tile with mine, and I think thats what they are made for.
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On 1/15/2011 11:49 PM, snipped-for-privacy@myplace.com wrote:

Yes, my brother has the diamond one. Not sure how it's made, but as it wears, it is always using new diamond grit as it goes. Doing my electric service he measured wrong and drilled at the wrong spot. It drilled through 12" block, filled with concrete, and some half inch rebar. The rebar is really tough on the diamond hole saw, although I always picture the concrete as harder to drill through.
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zAnonymous wrote:

You mean like hardiboard? I just used a cheapy arbor-type hole saw from harbor freight and it went through quickly and cleanly. Still working great, too.
Jon
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snipped-for-privacy@remailer.paranoici.org says...

This Harbor Freight carbide hole saw set works fine for that sort of stuff. The sizes are what you need and the whole set is only 20 bucks:
http://www.harborfreight.com/9-piece-tungsten-carbide-hole-saw-kit-90721 .html
--
DT



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