## Perfect miters every time

16

2

I'm using a table saw to make picture frames with mitered corners. It turns out that even tiny inaccuracies in the miter angle or the lengths of the frame pieces cause gaps that make a frame look sloppy. I know there are ways to fine tune a miter joint, like using a plane and a shooting board to trim the pieces. And there are specialty tools like a Lion Trimmer. But we're talking about fairly simple geometry here, so I feel like there must be some technique behind perfect, repeatable miter joints.

How can I create perfect miter joints every time without needing to measure each one veerrry carefully?

1I doubt this is an answer will stand on its own but are you using a mitre saw? Have you measure with a square that your blade is true? I did recently and found I was out by almost a degree. Had the same issue when I was making my frames – Matt – 2015-05-14T20:08:21.363

1@Matt I agree about making sure tools are properly adjusted, that's a great point. But I mean to ask here specifically about table saw techniques. – Caleb – 2015-05-14T20:13:20.433

2Yeah.... I missed the part about table saws. Sorry about that. The sled is a great answer. – Matt – 2015-05-14T20:19:12.980

3It may seem counterintuitive, but measuring is often the enemy of precision in the shop. Parallax and even the thickness of a line on a scale will challenge your ability to set up equal-length or perfectly-mated cuts. Use stop blocks, and gauge against known reference surfaces. – rob – 2015-05-14T22:24:31.943

@rob Although certainly related, repeatability and precision aren't synonymous. An operation can be precise without being (easily) repeatable, or repeatable without being very precise. Maybe a question for meta. – Caleb – 2015-05-15T13:42:04.880

19

There's two ways that immediately pop to mind- one involves spending a significant amount of money, the other a significant amount of time.

You can buy replacement miter gauges for most table saws (e.g. Incra) that are very very accurate. Couple that with a good tune-up, and you'll be cutting perfect miters in no time.

However, the other option is to make a nice miter sled.

Both options will provide a nice stop block system, which will give you exact, repeatable lengths. Couple that with accurate angle measurements, and you're really good to go.

1The slick thing about a miter sled is that the only measurement that matters is the "finished" angle. It works regardless of the two sides are exactly 45 degrees. As long as they add up to 90 (or whatever angle you're shooting for) it doesn't matter if one is slightly more acute and the other is slightly more obtuse. – rob – 2015-05-14T22:29:43.680

3@rob, that's true if a 90 degree angle is all you care about. But with a 90 degree angle that isn't perfectly bisected, the faces of the miter won't be the same length. You could just reduce the width of one of the pieces and it might work out though! – lars – 2015-05-15T03:28:10.600

10

The miter sled and precision miter gauge suggested by TX Turner work great for picture frames since your table saw's maximum depth of cut does not become a limiting factor.

To make mitered boxes--including shadow boxes with mitered corners--there is another technique that works well, which involves tilting your saw blade and using a crosscut sled.