How to Calibrate a Miter Saw: Pro Guide
We used a good bit of digital ink writing about miter saws in our Pro Guide series. If you’ve missed any series installments, they are great resources, if we do say so ourselves! For this edition, we’re looking at how to calibrate a miter saw. What good is a great saw on paper if it makes inaccurate cuts on wood? So before you go making some sawdust with that ol’ miter saw (or better yet, a shiny new one), be sure it’ll make true cuts. You’ll also need to tune it up occasionally over its life. Here are some Pro tips.
How to Calibrate A Miter Saw
We have a saying around here: it’s wise to de-energize. Before inspections and adjustments, either unplug or remove the battery from the miter saw. Yes, there are now battery-powered miter saws. And although they aren’t suited for all projects, they are awesome. Here are a few to check out:
Inspect The Blade
If your crosscuts, miters, and bevels aren’t as tight as they should be, the culprit may be a bum blade – or just a dirty one. It’s the easiest place to start your investigation. A little visual inspection goes a long way. Carefully spin the blade and look for warps, bends, or any other irregularities. If you find any, it’s time for a new blade.
But you might be able to improve your cuts and extend the blade’s life simply by cleaning it. Pitch buildup, sap, adhesives, and general gunk can accumulate around the teeth, gullets, and in a concentric ring around the broadside of the blade. Solvents – including some homemade concoctions we’ll discuss in a different article – can get you back on the road to true cuts quickly.
The major tool manufacturers make miter saw tables to tight tolerances. But there’s a slim chance that a new saw – and perhaps a larger chance that an older saw – will have an untrue table. To test it, put a reliably flat level on edge across the table. Now inspect for gaps between the level and table – on each end and in the center. To really dial in the inspection, try to slide a sheet of paper underneath the level to reveal gaps you might not be able to see.
In contrast to other miter saw adjustments, making an out-of-whack table true is somewhere between difficult and impossible. If a couple sheets of paper can fit in the gap, then the table could be ground/scraped or pressed flat at a machine shop. If a larger gap exists, you should probably go shopping!
Square Up The Fence for Good Miters
Believe it or not, your miter saw fence might not be square to the table. Kickbacks and other use/abuse can knock it out of alignment. To find out, pull the blade down to its fully depressed position and lock the arm in place using the pin. Pull the articulating blade guard up and out of the way so you can place a square of some sort – combination or even the plastic triangle that comes with many saws today – against the blade and fence. Any gap between the square and the blade or fence means the blade won’t cut 90° – and won’t cut accurate miters, either.
To rectify the problem, loosen the bolts holding the fence to the table and square it up. Then carefully tighten the bolts, making sure the fence doesn’t move in the process. Some saws have a solid fence while others have a split fence. You can square one side of the split fence and then use a level to align the other to the first.
Take It To The Next Bevel
Now it’s time to true up the bevel angle. Use the 45° or hypotenuse of your square and tilt the saw to its 45°. If there’s a gap between the blade and the 45° of the square, use the bevel adjustment bolt (often located near the back of the miter saw) to bring the bevel into alignment.
A Quick Note
Many saws have immovable miter gauge scales with the hash marks and numbers stamped into the metal. On these, you can loosen the screw on the indicator to give it a little adjustment. Once you’re confident that the fence is square to the blade and the bevel angle is accurate, take a quick look at the miter gauge. Does it match your adjustments? If not, you can bring the gauge into alignment with just a Phillips head screwdriver in most cases.
If it’s way out, some miter gauges are held down by a few screws to let you adjust them.
Checking Your Work
A quick way to check a miter saw’s accuracy is the Flip Test (we might have made that name up). But it’s quite simple: set your saw up for a 90° cut and shave the end off of a piece of lumber. Then make another cut, only this time make it a few inches long. The length doesn’t really matter. Now, flip that newly created piece over so that the shaved end butts up to the end of the second cut and be sure both pieces are firmly against the fence. If the miter wasn’t a perfect 90°, you’ll see a triangular gap between the pieces. Adjust accordingly. You can also perform the same test with bevel cuts.
How to Calibrate A Miter Saw: Epilogue
A little Google searching will reveal several different methods – from simple to sophisticated – for how to calibrate a miter saw. We’ve boiled it down to the methods that we think represent the most bang for your (time) buck. If you’re a Pro and have some tips on how to calibrate a miter saw, add them in the comments below.