Table Saw Explained, Arbors, Motors, Blades Tilting, and Fences

Arbors

The arbor is the shaft that the blade attaches to. It has a machined in flange on it's right side to stop the blade from sliding too far over and a threaded shaft that takes a large "cup" type washer and a nut to hold the blade on. These threaded shafts are always threaded in the opposite direction of the rotation of the blade so that the more the saw blade turns, the tighter it gets. The quality of an arbor lies primarily in how much 'run-out" it has.

Run-out is the amount of wobble from right to left as the arbor and blade spin. This too is most accurately checked with a dial micrometer but, if it's too bad to be acceptable, most people can see the wobble of the blade as it slows down when the motor is turned off. Run-out of less than .003" is considered 'wonderfully true' by most experts. Anything over .010" is considered poor and usually unacceptable. Quality threaded arbor shafts are machined to precise tolerances for more exact blade hole fit.

Note: The safest way to change saw blades is to remove the throat plate, cram a block of wood into the saw teeth at the rear and then loosen the nut. To re-tighten the blade, put the block of wood in front of the blade while tightening the nut. Do not use any metal object as this can bend saw teeth and break off carbide tips.

Many people also advocate unplugging the saw while doing this but this is often impossible with hard wired 220 volt tools and impractical with most others. However, be sure that all switches are locked "off" before working on any part of a table saw.

Motors

All cabinet saws use TEFC (totally enclosed fan cooled) motors because of the need to circulate more air around them in a closed cabinet. These are also totally dust proof and last far longer than ODP (open, drip proof) motors that are found on most other shop power tools. They're all at least 12amps at 220volts with the big ones ranging as high as 30 amps at 440 volt three phase. The "average" is 20 amps at 220volts (rated 3HP) and single phase.

All but the cheapest have magnetic switches that will not go on if there's no power to begin with and automatically cut off and stay off until reset if the power's interrupted. These are safety devices that prevent the motor from coming back on if you accidentally throw a breaker at the circuit box or there's a power failure while you're operating the saw. While allegedly controlled by a gizmo on the motor called a capacitor, these things can, depending on their design, also lessen the amperage draw on circuit breakers when starting the motors and, again depending on their design, give the motors a "softer start" as opposed to jerking wildly as the current hits the motors when the switch is thrown "on."

Depending on the brand and model, power is transmitted from the motor by one (1) to three (3) "V-belt's" running thru pulleys so that the 3,450 RPM motors turn the 10" blades at anywhere between 4,000 and 5,000 RPM (depending on the manufacturer).

Contractor's saws run on 110v, although all but the universal type motors can be rewired for 220v. They're generally all in the 1.5HP range, with motors that draw between 12 and 18 amps at 110v. This is more than sufficient power to cut 1" thick hardwoods all day long.

Unlike cabinet saws, which all have TEFC motors, some contractor's saws have the cheaper, and more prone to failure due to dust buildup, ODP motors. A few use induction type motors. Contractor's saws are designed to turn faster at the blade to compensate for less horsepower. Most turn 4,800 to 5,500 RPM. A few can turn as fast as 6,500 RPM.

Blades Tilting, Raising and Lower

Blade height can be lowered or raised by means on a hand wheel or crank mechanism on the front of the saw. A blade tilt mechanism is located on the side of the saw's cabinet, and operates in a similar manner to tilt the saw's blade angle as compared to the table when an angled cut is needed.

Blades raise and lower using a 2 bevel gear system or a ratchet type mechanism and a rack and pinion system for tilting the arbor in most models. The number of turns per inch on the raising screw determines how easy and how fast the blade can be raised or lowered and tilted to and from a given angle and it does vary from manufacturer to manufacturer.

Fences

Next to the motor, the most important part of any table saw is its fence. A good one locks tight, does not move after being locked and has some sort of device that utilizes a self stick measuring tape and a pointer to set precise distances from the blade for making rip cuts.  A rip cut is a cut made with the grain of the wood, sometimes known as "long cuts”.  Regardless of type of fence, it should be absolutely to the blade to prevent kickback of stock or burning and premature bearing and blade failure! If you can't get your fence absolutely parallel to the blade and keep it there without wobbling or moving, the most viable option is to set the back end (behind the blade) a few thousandths of an inch wider than the "business end" (the part of the fence that is in front of and alongside of the blade itself).

Generally, the aftermarket brands of fences are far more accurate than the standard fences that come on the cabinet saws sold in the world today. Unless one of those upscale fences is standard equipment in the first place.   

Note:  After market fences come in a variety of cutting widths: 30" - 40" and 52" being the norm.  While these fences all come with mounting rails that have dozens of holes drilled in them for mounting to various saws, you might as well plan on having to drill at least a few holes in the edge of your saw table or your extension wings to make them fit your particular setup.

Continue toMiter Gauges, Throat Plates & Splitters and Guards Table Saw Blade and Dado BladesTable Saw Explained, Part III

Return to Part I:  Table Saw Explained, For the Beginner



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