Table Saw Alignment

What

A sliding table is your best choice for cross cutting large panels.  Instead of being guided by a bar in a miter slot, the sliding table runs on rails - often with ball bearing slides.  Some industrial machines utilize a sliding table for all cross cuts and don’t even have a miter slot.

There is one aspect of sliding table alignment which is very similar to aligning a miter gauge: squaring up the fence.  But, that can only be done properly when the table height and travel are properly adjusted.  On a Table Saw which has both a miter slot and a sliding table, the motion of the sliding table should be aligned parallel to the miter slot (which is also the alignment reference for the blade and the fence).  On saws which have no miter slot, the motion of the sliding table becomes the alignment reference.  The blade and fence are aligned parallel to the motion of the sliding table.

Most people recognize the folly of attempting to align a sliding table by holding a square between it and the blade.  The issues I raised describing this procedure in the miter gauge article get magnified with the larger dimensions of a sliding table. 

Unfortunately, darn few recognize the folly of using a test cut method for aligning a sliding table.  Traditionally, a large square panel (piece of plywood or other sheet good) is sacrificed in what is called the “four cut method”.  An edge is cut and the panel is rotated so that the freshly cut edge is against the sliding table fence.  Then the next edge is cut and the panel is rotated again so that the freshly cut edge is against the sliding table fence.  The next edge is cut and the panel is rotated again.  Finally, the last edge is cut.  If you follow the process, any error in the angle of the cut will be added to that of the preceding cut.  Essentially,  measuring the angle between the first and last cuts with a square (typically a framing square) will show the alignment error multiplied by four.  Then, as the advocates say, it’s a “simple” matter of adjusting the fence on the sliding table to eliminate the error.  So, if you have a lot of spare time, and a big budget for turning sheet goods into sawdust, then this is a great method.  Fortunately, there is a better way!

Why

If the sliding table doesn’t travel in a plane parallel to the main saw table, then the depth of cut will vary.  This might be OK when you are cutting through a panel, but it’s not so good when you are cutting dadoes. 

Then, if the table doesn’t travel parallel to the miter slot (or blade for those machines that don’t have a miter slot) then you can see poor quality cut, burning, wandering, and sawdust in the face exactly as if the blade was poorly aligned.

Finally, if the fence isn’t squared up with the travel of the table, then the cuts won’t be square.

How

View the video…

Read the text…

 

The first step is to adjust the height and travel of the sliding table so that it matches the main table of the saw.  A good long straight-edge is essential.  A long level (like this one) will handle the task nicely.  Place it across both tables in several locations checking for gaps.  Adjust the height of the sliding table so that it is in the same plane or very slightly higher than the main table.  Be sure to check that the tables remain co-planer as you move the sliding table through its travel.  The alignment is important, but it’s not critical so a more elaborate jig (with a dial indicator) isn’t necessary.

Next, place a large indicating square against the sliding table fence as shown.  Its size should be close to the largest cross-cuts you anticipate using the sliding table for.  There is a detailed description of indicating squares in the miter gauge article so I won’t repeat it here.  However, it doesn’t hurt to emphasize the importance of accuracy.  A framing square just isn’t going to provide good results.  Move a stop into place to prevent the square from sliding around.

To align the travel of the of the sliding table, move the dial indicator jig to the base of the square and zero the indicator.

Now move the dial indicator jig and the sliding table together.  Any change in reading indicates that the sliding table is not traveling parallel to the miter slot.  Adjust the travel to minimize the change in reading.

Now, move the dial indicator jig to the far end of the square.

Push the sliding table forward and zero the indicator at the base of the square. 

Pull back the sliding table and observe the reading on the dial indicator.  A change in reading indicates how far the fence is from being squared up.  Adjust the fence to bring the reading back to zero.

Push the sliding table forward again and re-zero the indicator.

Pull the sliding table back and observe the reading.  The error should be considerably less.  Adjust the fence to bring the reading back to zero and check again (push forward, zero the indicator, pull back, check for error).

Ed Bennett
ejb@tablesawalignment.com