Table Saw Alignment

What

Blades are not perfectly flat, arbors are not perfectly straight, and flanges are not perfectly true.  They all wobble a bit.  This “wobble” is generally referred to as “run-out” and it can be caused by various problems:

- Warped blade
- Bent arbor
- Poorly faced flange

The goal of these procedures is to determine if any of these problems exist to an extent that they will adversely affect the performance of the saw and fix them as necessary.

Why

All of these conditions will produce a blade that wobbles back in forth while it spins.  This will produce a very poor quality cut and a kerf that is wider than the teeth. 

How

View the video…

 

Or read the text… (and get more info)

Start with the same setup you used to check for bearing side play.  The Offset Bar on the end of the dial indicator plunger isn’t necessary, you can place the stylus anywhere near the edge of the blade.  It doesn’t need to be near the table surface.  Rotate the blade by hand and observe the reading on the dial indicator.  If you are aligning a contractor’s style saw, then turn the blade by pulling on the belt.  If it’s a cabinet saw, then you’ll have to do it by touching the blade.  You have already seen how flexing of the blade can influence the reading so do your best to avoid it.  Basically, you want to measure variations in the surface of the blade (its flatness) combined with any wobble in the arbor and arbor flange (run-out).  You want to avoid changes in reading caused by flexing the blade or bearing side play.

When you locate the point with the highest reading, mark the spot with a felt tip pen.

 

Loosen the arbor nut so that the blade can rotate freely without turning the arbor. 

With the arbor remaining still, rotate the blade half way around (180 degrees) and re-tighten the arbor nut.

Now, with the dial indicator stylus against the blade as before, watch the reading as you rotate the blade.  Stop when you find the highest reading.  If you find the spot that you marked with the felt tip pen underneath the stylus of the dial indicator, then the variations are being caused by blade warp.  If the total change in reading by less than +/-0.001″, then your blade, arbor and flange are in great shape.  If it’s more, then you might want to think about getting a better blade, but there’s no reason to be concerned with the condition of your saw.

However, if the highest reading is nowhere near the spot you marked, then the variations are being caused by wobble (run-out) in the arbor and/or the flange.   The next steps will reveal exactly where the problem is.

Remove the blade and the throat plate so that you can place the stylus of the dial indicator directly against the arbor.

This close up photo shows the stylus resting on an unthreaded portion of the arbor.  You won’t be able to obtain reliable readings if the stylus is on the threads.  If your arbor is threaded all the way up to the flange, then you won’t be able to measure arbor run-out.  Also notice that the flange is dish shaped.  If the dial indicator were exactly vertical, then the plunger would rub against the outer edge of the flange.  So, the dial indicator has been tilted slightly so that there is clearance between the plunger and the flange.  Normally, your most accurate and reliable measurements occur when the plunger of the dial indicator is perpendicular to the surface that you are measuring.  This is one of those rare instances when you need to break this rule.  The tilt is slight so the effect will be negligible.

Next, you want to rotate the arbor and observe the reading on the dial indicator.  It’s easiest to do this with the belt(s) removed.  The change in reading should be less than 0.001″.  If it’s more, then you should replace the arbor or forget about using this saw for precise work.  This mode of run-out is caused by a bent arbor.  It could be a defect in manufacturing but most often it is caused by a kickback (wood binding in the blade during the cut).  The problem cannot be easily corrected in a machine shop.  A shop which specializes in straightening crank shafts might be able to do it but the cost would easily exceed that of a new arbor.

In preparation of measuring flange run-out, tilt the arbor to 45 degrees.  Place the stylus of the dial indicator against the outer rim of the flange.  Notice how the dial indicator is tilted to match the tilt of the arbor.  This arranges the plunger so that it is perpendicular to the surface being measured and will give you the most reliable and accurate readings.  I’ve seen a number of people (authors, manufacturers, and other so called “experts”) demonstrate this measurement by leaving the arbor horizontal and tilting the dial indicator at a steep angle.  This is a very poor practice that will cause the readings to be exaggerated.  Now you know better than these “experts”.

The close-up photo shows the stylus tip resting on the center of the raised rim of the flange.  This is the part of the flange that contacts the blade and is therefore the only part that matters.  As before, rotate the arbor and observe the reading on the dial indicator.  Removing the belt(s) will make the task a lot easier.  You should see no more than 0.001″ variation.  If it’s more, you can bring the arbor to a machine shop and have the flange faced on a lathe. 

So, what happens when you do all these tests and find nothing wrong?  The blade seems flat, the arbor isn’t bent, and the flange runs true but you still see excessive run-out when you measure at the edge of the blade.  Look for a piece of dirt, saw dust, or grime on the flange, or on the blade where it contacts the flange.  Make sure that all the mating surfaces are clean before re-assembling and testing again.  The problem could also be a burr or ding on the edge of the flange.  A couple of swipes with a file could clear it all up.

These photos show the tests being demonstrated on my mid-80’s vintage Delta Unisaw.  It has seen really hard use during the past 20+ years.  In addition to thousands of board feet of lumber, this saw has seen many tons of aluminum across it’s table.  Even so, it’s still accurate and still passes these simple diagnostic tests. 

Ed Bennett
ejb@tablesawalignment.com