In this Instructable I'll show you how to cut grooves down the center of boards without the need to measure. Cutting centered grooves is a really quick and easy process and doesn't require measuring or a dado blade. Many times this process is faster than setting up your dado blade to the proper width, especially if you only have a few boards to cut.
Step 1: Set Your Blade Height and Fence
OK OK.... So you do need to measure a little, but this is just to set the proper height of the blade. After the blade height is set slide your fence over until the board you are cutting the groove down appears to be centered above the blade.
Step 2: Make Your First Cuts
Turn the saw on, make your first cut, and then flip the board 180 degrees so that the edge that was previously riding against the fence is now facing outwards and make another pass through the blade. Once you've made these two cuts turn the board over and inspect the two cuts in order to see how far apart they are.
Adjust your fence in towards the blade less than the width of one blade kerf and make two more passes in the same way you did earlier. One pass, flip the board 180 degrees, and then a second pass.
Continue this until all the excess material has been removed and you're left with a clean groove.
Step 3: Widen the Groove and Check for Final Fit
Once you've got a smaller grove down the center you can continue the process of making cuts on each side of the groove and adjusting the fence until you feel you are getting close to the final width you need, then you can start checking for fit.
One thing to remember when you're adjusting the fence between cuts is to move it less than the width of a blade kerf each time.
Step 4: Make Final Cuts and Fit the Board
Once you're close to the final width you need to accommodate the board thats going in the groove you'll want to start making even smaller adjustments to your fence in order to sneak up on the exact width.
It's important to remember that each cut you make effects both sides of the groove so when adjusting your fence move it 1/2 the distance you need in order to avoid over shooting it.
Continue to make test fits and very small adjustments to the fence until you get a nice tight fit.
Thank you very much for checking out this Instructable! I have included a link to my youtube video on this process that may give you a better idea of exactly how its done. If you like that video please be sure to subscribe so you won't miss out on my future content.