Adjusting Miter Gauge Model

[Sawduster]

On one of the woodworking forums there was a discussion about the proper method of adjusting a miter gauge for getting square cuts on a table saw. Some were argueing that one should set the gauge square to the blade, while others said the gauge should be set square to the bar on the gauge, and thus to the miter slot on the saw table. In a perfect world, the blade of the saw would be set perfectly parallel to the miter slot and therefore either technique should work since they are indexed to each other. But for very long miter cuts on wide pieces of stock, any small amount of error will be magnified, so which method would give you the most accurate cut allowing for some minute error between the blade and the miter slot?

While some are adept at working this type of thing out in their heads, I need visual representation and proof, so I created a SU model of a table saw table, blade, miter slot, miter gauge and even some scrap wood to test it out on. That model can be found here:

http://www.sawdustersplace.com/Storage/TSCut.skp

Using the model I tested both methods with the blade intentionally tilted 2 degrees out of parallel with the miter slot. First I squared the gauge face and scrap wood piece to the blade, created a group of the scrap board, gauge and bar and carefully slid the group, keeping the bar in the slot by keeping the move on the proper axis until the front edge of the blade contacted the leading edge of the wood. I marked both edges of the blade onto the wood, then coninued the move, stopping and marking both edges of the front and rear of the blade to both the leading and trailing edges of the board. I then copied the board and moved it off of the saw table and connected the corresponding marks on the leading and trailing edges of the board to each other with lines.


Here is the resulting still of the board. Note that the lines are all 2 degrees off from perpendicular, equal to the error induced in the blade to miter slot. Note also that the two outside lines would denote the kerf width of the cut which is quite wide.

I ungrouped the board, gauge and bar and adjusted the gauge and wood square to the bar, regrouped them and repeated the above, leaving the blade to miter slot error the same as the initial setup.


The results of this setup show again a wide kerf, but the lines of cut are at 90 degrees to the edges of the board.

The wide kerf in both instances is indicative of both a rough cut and a cut which would try to pull the workpiece along the gauge. Admittedly, 2 degrees is a huge amount of error between the blade alignment and the miter slots, but every setup has some degree of error regardless of the method used for adjusting the blade to the table and that error is magnified over the length of any cut made using the one to guide work through the other, so your best results are obtained by squaring the gauge to the slot as then you have only what error there is in blade rotation to contend with.

[remus]

Cheers jerry, thats a very thorough explanation/imvestigation.