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Saturday, February 5, 2011

Essential Table Saw Tune-Up

Tuning the table saw: it's something my friend Dave - a carpenter - never really did.  But over my last ten months of woodworking, I've come to realize how important it is when making furniture.  That's because, unlike in carpentry, where poorly-fitting joints can be saved by screws, nails, and shims, perfect angles are critical to good furniture.

I use my table saw for many joinery operations.  Not only do I use my table saw to rip stock (after jointing and planing the other three faces), it's also my go-to choice for cutting square ends and miters.  the table saw excels at these tasks because it's possible to tune the saw to within 1/100 of a degree of accuracy, unlike other power tools, such as the miter saw (the best of which, by the way, could never be relied upon to cut miters for furniture). 

I like to tune my table saw before every cutting session, and sometimes in the middle of one.  That's because both the fence and the blade can drift from their settings during the cutting process, raising the blade, etc...  And I would bet that if you take the time to tune your own saw, you'll notice that it's out of tune more often than you'd like to believe.

When it comes to tuning, there are only a few parameters to check:
  1. Check that the blade is parallel to the miter slots in the table (if you'll be using the miter slot)
  2. Check that the fence is parallel to the blade (if you'll be using the fence)
  3. I like feeler gauges for tuning
  4. Check that the blade's cutting angle is set properly (for ANY cut you do)
Squaring the Blade to the Miter Slot:
The process for squaring the blade to the miter slot and fence is similar for both.  There are many ways to do it.  I used to square the blade to the miter slot or fence by sliding one leg of a big, accurate framing square up against the flat of the blade,  and the other leg flat against the fence of the sled in my miter slot.  Of course, any inaccuracy in the sled's fence can confound things, so the calibration step is really two steps in one: making sure the sled's fence is perpendicular to the miter slot, and making sure the blade is parallel to the miter slot. 

First i check the gap at the front...
First, I check the blade's orientation to the miter slot by placing the fence of a marking gauge in the miter slot, and extending the cutting disc to the flat of the blade.  Then I slide the marking gauge along to the opposite side of the blade, and ensure there's no gap between the cutting disc of the blade, or between the fence of the marking gauge and the miter slot's edge.

Second, I take that big framing square, put one leg on the sled's fence, and the other leg up against the saw blade.  To check for squareness, I look for gaps between the framing square and the blade.  But I don't look with my eyes.  Instead, I use a feeler gauge.  This lets me sense gaps that are too small to see, down to 0.001"

Squaring the Blade to the Fence:
...then I check the back
I also use the feeler gauge for this step.  First, I pull the fence as close to the full-raised blade as possible, without hitting the teeth.  Next, I find a combination of feeler gauges that will fit snugly between one tooth of the blade and the fence.  Third, I take that same group of feelers, and, finding another similar tooth on the other end of the blade, try to stick them in between the second tooth the the fence.  If I can't fit them into the gap, or if I can wiggle them at all, then I know I need to adjust the fence accordingly.

Setting the Blade's Cutting Angle:
This is the tune-up that's most important to perform regularly, as often as every few cuts.  The reason is, the cutting angle of the blade can drift wildly, since it's set with a hand-wheel on a worm drive, and this wheel is subject to lots of vibration during a cut.  Even if you lock the wheel's position with the locking nut, it's still prone to slipping. 

I love my "Tilt Box"
To set the cutting angle, you can use an engineer's square and look for light between the edge of the square and the edge of the blade.  It's not a bad way to do things. But for setting the blade to any other angle than 90 degrees, I prefer to use a digital level.  My digital level is called the "Tilt Box", and it's given me accurate readings without hassle for months. 

Once everything is tuned up, I'm ready to cut with confidence, knowing that - as long as I do my part in keeping the stock on the fences & the table top - I'll get the cuts I expect from my table saw.


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