Chris McLeester
04-11-2017, 9:26 PM
I've been struggling to make centered grooves in cabinet door rails. I spent some time doing some algebra today and thought I would share my formula. Now I have to actually learn how to feed the stock through. I'm even using a featherboard but get a groove that is unequal width at spots (table saw is well-tuned).
The formula assumes that you will make one groove, turn the piece so the other side faces the fence, and run it through again. This centers the groove.
x = Where to set the fence!
T = thickness of material
G = desired size of groove
K = kerf of your saw
x = (T + G - 2K) / 2
Now, it may be tough to hit this exactly -- so here's a formula for exact center. You can move the fence out from there:
x = 1/2 * (T - K)
So, if you are trying to cut a 1/4" groove in 3/4 material your final fence position will be 3/8".
x = (3/4 + 1/4 - 2 * 1/8 ) / 2
x = 3/8
But you might be better off starting at 5/16" (halfway) and working your way out until you have a tight fit.
x = 1/2 * (3/4 - 1/8)
The formulas should work for different thicknesses, grooves, and kerfs. Obviously, G cannot be smaller than K - hard to make a groove smaller than your saw blade. Also, for grooves wider than 2 kerfs, it will establish the outside lines of the groove.
The formula assumes that you will make one groove, turn the piece so the other side faces the fence, and run it through again. This centers the groove.
x = Where to set the fence!
T = thickness of material
G = desired size of groove
K = kerf of your saw
x = (T + G - 2K) / 2
Now, it may be tough to hit this exactly -- so here's a formula for exact center. You can move the fence out from there:
x = 1/2 * (T - K)
So, if you are trying to cut a 1/4" groove in 3/4 material your final fence position will be 3/8".
x = (3/4 + 1/4 - 2 * 1/8 ) / 2
x = 3/8
But you might be better off starting at 5/16" (halfway) and working your way out until you have a tight fit.
x = 1/2 * (3/4 - 1/8)
The formulas should work for different thicknesses, grooves, and kerfs. Obviously, G cannot be smaller than K - hard to make a groove smaller than your saw blade. Also, for grooves wider than 2 kerfs, it will establish the outside lines of the groove.