Why Are My Miter Cuts Not Lining Up

Why Are My Miter Cuts Not Lining Up

Miter cuts give such a professional and aesthetically pleasing appearance to picture frames, window and door trim, even framed tabletops.  When the 45-degree cuts create perfect miters and the joints align as one, it’s a happy feeling.

But, when the cuts are off slightly, our eyes are drawn to it like ants to honey and we can’t help but notice them every time we look at the painting on the wall or sit down for a meal at that table.  In woodworking, there’s nothing worse than bad angles and uneven corners.

Why, we ask?  Jeepers, I did everything correctly, I thought, with my miter saw or table saw.  The project was supposed to be so easy – make the cuts, add a little glue, maybe use biscuits or corner staples to secure the pieces, and it’s done.  

What Do I Do Now?

How To Fix Bad Miter Cuts

Miter Cut

The two most common causes of miter cuts that just don’t fit the way we want them to is because:

  • We cut one piece too long or too short.  If you cut the piece too long, there will be an overhang on the outer corner.  Since that is the thin end of the cut, that overhang can be pliable, meaning it can be folded over just a little bit to meet the other piece smoothly.

Something metal can do this for you, perhaps a screwdriver or the flat blade of a firm ruler.  Be gentle, and apply only enough pressure to fill in the gap.  This technique will work well if the gap is small.  Fold the grain over, hide the gap, and go lightly on any sanding.

  • The blade of the saw we used was not perpendicular to the base.  This gap is going to be something you’ll need to fill, but don’t fret.  If the gap isn’t too large, and you don’t want to adjust the blade on your miter saw back to perpendicular to recut the pieces, a little glue and some saw dust will do the trick.

Because the pieces will not align properly for a tight joint, you’ll want to use biscuits to give you more wood surface to glue.  Add plenty of glue to the biscuits, enough to spill well over the entire surface of the gap.  Then, add and rub in saw dust from the same wood, letting it mix with the glue to create a matching wood filler.

We wrote about DIY wood fillers in previous articles, including here and here.  Making your own wood filler for small holes and gaps is easy, and it works well.  You’re likely to have what you need already in your shop – glue and saw dust.

  • Of course, the third way is simply to start all over again, being sure to measure your pieces carefully, and ensuring the blade of your saw is perpendicular to the saw’s base.  But, consider the first two options first, as they can help you avoid an entire do-over.

How Do I Make Sure My Miter Saw Is Accurate?

There are several tests you can conduct on your miter saw to determine that everything is aligned properly to give you an accurate and true cut.  Some inspections are obvious and results can make corrections and adjustments easy; some become a bit more involved.  

Here are some to consider:

The blade.  Blades can become damaged over time, so start here.  Unplug the saw and inspect the blade for flaws like warps, bends, and broken teeth.  These are the easiest to inspect, and if any defects are noted, it’s time for a new blade.  

The table.  Make sure the table is level.  Using your most trusted level, look for any gaps between the table surface and the level, in addition to determining it’s true.  Make any adjustments to the table based upon this inspection.

The fence.  Unplug the saw and pull the blade all the way down, locking it into that position.  Then use your speed square to determine that the fence is properly aligned by holding it against the fence and the blade.  If it’s not aligned, adjust accordingly until it is.

The miter gauge.  Adjusting the miter saw’s gauge is not a difficult task.  For miter saws that have immovable gauge scales, with hash marks and numbers actually stamped into the metal, simply loosening a screw on the indicator will enable you to adjust the gauge.  After making sure the fence is square to the blade (the previous test), check the gauge to see if it matches your adjustments.  If not, continue to work the gauge adjustment until it does match.

How Do I Make My Miter Joints Tighter?

The surfaces of the wood being jointed in miter joints is end grain, and end grain soaks up glue very well.  Gluing miter joints can last for years, even as the wood expands and contracts, since all of the pieces will expand and contract together.  

However, eventually, the joints will weaken (perhaps over many years, though), so tightening the joints from the beginning can eliminate the need to repair them at that future date.

The easiest way is to use a nail.  You do run the risk of splitting the pieces, though.  A brad nailer is another option, again an easy and quick solution.  Either of these will leave a hole, though, so you’ll need a little filler or putty, and some sandpaper, to do what you can to hide it.

Makita AF506 2" Brad Nailer, 18 Gauge

We’ve already suggested the use of biscuit joinery for tight corners.  In fact, we’ve written about it in previous articles, including here.

It gives you more wood surface for gluing, and provides a tighter fit that is well aligned.  Biscuits are inexpensive, and a little glue is the rest of the expense.  If you have a biscuit joiner handy, it’s an easy task.  

Splines will also work to tighten the miter joints. Even using a biscuit to create the spline will work. 

There are also corner staples that you can apply to the back of the joint where they will not be seen.  The most common staples used for corner joints include the standard D-shaped staple, V-nails, and cable staples.  These are inexpensive and easy to find at your local hardware store, the large DIY stores, and even from online retailers.

Rather than go on about the numerous ways to tighten your miter joints, here’s a video that offers 10 different ways with demonstrations for each.  Some are a bit involved and will require tools you may not have in your shop.

Check your saw and its component parts, make all necessary adjustments, and get the miter cuts right the first time.  Or, if you at least get it close, you now know how to fix a cut that doesn’t quite make it.  And, if you want to make the fit and connection even tighter, you now have a bunch of options to choose from.

Then, you have that professional and aesthetically pleasing appearance you were hoping for in the first place.