External Influences on the Accuracy of Machine Settings
Setting your machines using TS-Aligner can help you completely avoid the need for test cuts. However, it's possible that accurate machine settings do not produce accurate results. Certain conditions can thwart your efforts to obtain accurate machine alignment.
Blade Flatness
If you encounter a blade warp during alignment or tilt setting it can easily fool you into thinking that your adjustment is accurate when it really isn't. So, it's important to first check your blade flatness before you make any other adjustments. This can be easily done with TS-Aligner. If you detect excessive warp (more than 0.004" total) then the best thing to do is replace the blade. If you must use a warped blade, then it's possible to obtain extremely accurate alignment by making a mark on the blade body and taking all your readings with the dial indicator stylus on that mark. Rotate the blade as necessary to move the mark to the desired location before taking the reading. The technique is demonstrated in the TS-Aligner Jr. video and is far more reliable than using a blade replacement plate.
Blades can also flex under the pressure of cutting. While they are quite useful on lower powered saws, thin kerf blades flex much more than standard blades. Taking a full cut, rather than a thin shaving will help reduce flexing. If you encounter problems with accuracy , especially if you notice that the cuts aren't straight, then switching to a standard kerf blade will likely be the answer.
Table Flatness
If your table surface has significant warp to it then your alignment and settings will be adversely affected. Such a condition can be detected using a precision straight edge. There's really nothing that you can do to compensate for or avoid such a problem. The problem should be corrected by having the table replaced or reground at a machine shop.
Don't overlook the flatness of your table insert. Be sure to level it carefully. If it is excessively warped you may need to get a replacement.
Fence Flatness
If the fence flatness is less than 0.005", you're fence is probably fine. Anything greater than that and you should see if you can get the problem repaired or get the fence replaced. You may have to bring your fence to a machine shop to have it milled or ground flat. The danger here cannot be minimized. Fixing a fence flatness problem will not only make your saw safer, but you will regain control of your rip cuts. They will not wander away from the fence, or be pinched between the fence and the blade.
It is potentially very dangerous to attempt to use a warped fence for rip cuts. If the board you are cutting becomes pinched between the fence and the blade, you will be lucky if you are not seriously injured. Don't try to align a warped fence. Repair or replace it and then align it.
The fence can also flex under the pressure you apply during the cut. The symptoms are very similar to those of a poorly aligned fence. Aluminum fences flex more easily than steel fences. If you determine that this is a problem, the far end of the fence can be clamped down to the table surface.
Dust
Any dust or dirt underneath your TS-Aligner can adversely affect the accuracy of your adjustments. Making sure that things are clean before making an adjustment or a cut will help ensure that the results will be accurate.
Clamping/Fixturing
If wood is allowed to move out of position while a cutting operation is underway, then the results will not be accurate and the situation can be potentially dangerous. Be sure to use clamps and/or feather boards whenever possible.
Creeping Adjustments
Sometimes vibration and cutting pressures can cause the adjustments on your machine to shift. You can tell if this is happening by checking the setting right after making the cut. Most adjustments have locking mechanisms to prevent this. You should use them whenever possible. A machine that cannot keep its adjustments during the cut will make accurate work difficult if not completely impossible.
Stock Preparation
Make sure you start with wood that is prepared with the same accuracy that you expect from your machine adjustments. This is probably the most frequently overlooked aspect of precision woodworking. It is most often overlooked by people using pieces of scrap for trial and error adjustments. An accurate miter can't be produced using a curved board. Accurate dado depth can't be obtained with a warped board. Take the time to make sure edges are jointed and surfaces are accurately planed.
Miter Slot Play
If the miter bar shifts in the slot during a cut then the results will not be accurate. Vibration and the forces of cutting make it very difficult to prevent. This is why most aftermarket miter gauges have adjustments for the fit of the miter bar. There are also aftermarket kits that you can use to modify your miter bar to eliminate play.
Last revised: January 21, 2006.