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Miter Joint Tips
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Having trouble getting your miters to fit together? It's not as easy as it sounds. Below, experts Michael Dresdner and Rick White offer some tips on the subject to a Woodworker's Journal eZine Reader:

Q. I often see small boxes with near invisible joints and would love to know how to make them. I have an excellent miter saw, a great table saw, and a wonderful planer, among other tools. My parts seem perfect -- squared and sanded and smoothed -- yet I still end up with gaps in my miters. Being a self taught woodworker, have I missed some basic, simple steps in joining angles, mitering corners, etc?

A. Michael Dresdner: "Three things come immediately to mind. First, check your tools. Cut a set of 45 degree angles, put the two boards together seamlessly, and check the outer and inner angles with a good square. Often, tools cut close to 45 degrees, but for invisible joints, they must be dead on. Tweak the tool if need be. Second, cut your miters after the wood has stabilized to the relative humidity of the assembly room. If a board expands by absorbing moisture, the miter will be open on the outside. If it contracts, the miter will open on the inside. Finally, be aware of your fit before and after glue up. Waterbased glue can expand a miter enough to throw it off, and too much glue will result in a visible glue line. Use the glue sparingly, and get the piece in clamps as rapidly as possible."

A. Rick White: "Is your material flat? The longer the miter you're making, the harder it is to make sure your work piece lies flat when you cut without cupping - especially when you're using a wider board. It's also possible when you're using solid lumber that your two pieces are from different logs, or even from different parts of the same board, and are not exactly the same thickness. Then, when you flip your miters together, you get gaps.

"You say you have good equipment, but have you checked things like how sharp your saw blades are? To get your miters right, all of your tools have got to be right on."

From the Woodworker's Journal eZine archives

We'd like to add that if you are cutting miters on a table saw and they aren't coming out, the problem may be your miter gauge. Are you using the miter gauge that came with your table saw? The typical stock miter gauge that comes with a table saw "is inaccurate and awkward because of its small body and single guide bar" - to use the succinct words of Kelly Mehler, author of The Table Saw Book. If that's the trouble, a precision miter gauge might be a wise investment. At least you could rule out bad angle settings as a possible cause.

If you really want to get angle cutting accuracy and versatility out of your table saw, think about coupling a precision miter gauge with the Incra Miter Express Miter Sled. It could have a dramatic effect on the quality of your woodworking in general - not just the fit of your miters.  To sweeten the deal, there's a significant price break if you buy the Incra miter gauge and the sled together in the Incra Miter Gauge Combo Value Package.

posted on November 30, 2006 by Rockler
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7 thoughts on “Miter Joint Tips”

  • Jim Cashman

    Re: Miters<br /><br />I am going to be making some small boxes and I was thinking of using a "miter joint" router bit for this. Would this be as accurate as what you have described for the table saw ?

  • Blog Editor

    <p>A <a href="" rel="nofollow">lock miter router bit</a> makes a tight fitting, exceptionally durable joint. But the advice from Rick White and Michael Dresdner offered above also holds true for lock miter joints. The stock needs to be flat, of uniform thickness and cut square for the end results to be good. The bits can only be used with a router table, and a power feeder or featherboards (at minimum) are highly recommended.</p><p>There are reports of a learning curve on the set up of lock miter bits. For 3/4" stock, the <a href="" rel="nofollow">Rockler Router Bit Set-Up Jig</a> can speed things up (see the <a href="" rel="nofollow">Set-Up Jig Instructions</a> for a look at how it works).</p><p>(Any further comments, tips or advice on this topic is encouraged)</p>

  • Steve Jones

    Been cutting tight gapless crown and trim for quite a while. Tweaking and adjusting as I go is the norm. Rooms seem to be more and more inaccurate as time goes on.<br /><br />However, just purchased a tool that I think will revolutionalize my trim accuract: that is the Irwin after market laser disk for the compound miter saw. <br /><br />I got mine here at Rockler with a new trim saw blade to boot. Tried it out and the line is visible even outdoors on a sunny day and on my saw, the laser line leaves the line. Perfect.<br /><br />Anxious to do a job with this. <br />Steve Jones

  • darrell


  • Blog Editor

    Darrell,<br /><br />Thanks for the question. An octagon has twice as many sides as a square so half the number of degrees in each miter. Four sides - 45 degree miters. Eight sides - 22-1/2 degree miters.<br /><br />You might want to look at this page on <a href="" rel="nofollow">calculating polygons</a>. You'll find a calculator for various regular polygon dimensions. Hope this helps.

  • Bill Fisher

    Would John care to share his plan for this bookcase? We have a year-old great granddaughter who would be able to put this to very good use in the not-too-distant future. All I would need are the dimensions and possible a rough sketch of the eave trim under the roof. Thanks. Bill

  • Rockler Blog Team
    Rockler Blog Team November 20, 2009 at 11:21 am

    Thanks for the comment. It's been a while, and we haven't heard from John. If you decide to take a crack at it anyway, let us know how we can help!

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