Fiber cement saw and shear tips
The best fiber cement saw is a good high quality table saw with a diamond tooth blade spinning at 6000 rpm. The blade would need an arbour almost 2/3 it's diameter to stabilize the blade as much as possible as it spins.
This would produce as perfect a cut as possible accurate to within +/- 1mm or +/-.030. This is the kind of setup used by the fiber cement manufacturers for their trimmed panel sizes. They also make use digital backgauges such as a Tiger Fence to assure consistent repeat cuts when there is a large quantity of panels to prepare.
Since fiber cement panels sometimes have to be cut on site a special circular saw can be used. Manufacturers typically ship untrimmed panels for this purpose.
The best fiber cement saw for working on site are circular saws purpose built for use with fiber cement such as the Mafell or Festool. Both these saws have built in dust collection as well as dust collection devices purpose built for collecting fiber cement panel dust.
Dust is an important concern because the fine dust produced by cutting panels is harmful even with the most expensive of saws breathing protection must still be worn.The Festo and the Mafell also have long accurate fence guides to aid in making long accurate cuts.
The blades for these saws are tungsten carbide as opposed to diamond tooth blades in the table saw. The feed rate is much slower for the tungsten carbide blades used in the circular saws. This is a compromise to produce accurate cuts in the field.
Another difference is the number of teeth on the saw blades. Fiber cement cutting blades for circular saws have only 4 cutting teeth. Popular blades are 7.25 diameter items made by Freud and Irwin.
These 4 tooth blades are made to get proper chip removal from the circular saw which can only spin at 1800 rpm unlike the table saw which can be set to spin much faster.
It is not reccomended to use diamond or silicon carbide cutting disks for fiber cement. The material is not as hard as stone and would be easily chipped using blades such as these.
Another option for the lower quality fiber cement siding boards is the fiber cement shear.The shear works by taking small nibbles. It works best with thinner softer composition boards such as Hardie Board.It does not work well however with more expensive panels such as SwissPearl and EuroPanel
The shears chief advantage is that it produces far less harmful dust than any of the saws making very handy for the jobsite. It also works well for thin panels used for ship lap applications