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I am thinking buying one of these https://www.amazon.com/Incra-MITER1000-18T-Miter-Miter-gauge/dp/B000051WSE/ref=sr_1_5?s=hi&ie=UTF8&qid=1483284237&sr=1-5&keywords=incra+miter+gauge

I have seen many guys using a table saw jig for this. Wouldn't the above be good enough?

MiniMe
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  • @Ashlar's answer is the usual way for making sure your picture frame miters match up. I will say the Incra miter gauge is very good, and I've gotten reliable miters with mine. But, 1. it is probably more expensive than making the miter sled, and 2. the miter sled is easier to use. With the miter gauge, you are constantly changing the angle back and forth between +45° and -45°. The sled has both angles built in. – Katie Kilian Jan 01 '17 at 18:20
  • I did not realize that I would need to change the angles back and forth, you are definitely right – MiniMe Jan 02 '17 at 12:40

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I cut miters under the assumption that getting to 45 degrees perfectly is difficult. My solution is to use a miter sled to make the cuts. The sled is uses a 90 degree angle set as close to 45 degrees to the saw blade as possible. If the angle is off a little it does not matter. Cut your boards placed on one side for one half of the miter and the opposite side to complete the joint. The sum total angle will always be 90 degrees.

Miter sled

Ashlar
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    that is a very smart observation...I did not think about that. With a gauge, if it has errors then the error is amplified when the two pieces are put together. Good point! – MiniMe Jan 01 '17 at 18:09
  • At a second thought I think that if the error is visible in your case it will look bad on the frame although the angles will be 90 degrees – MiniMe Jan 01 '17 at 18:11
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    The miter sled is set as close to 45 degree as I can make it. The angle difference is so slight as to be not detectable. – Ashlar Jan 01 '17 at 18:17
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I have seen many guys using a table saw jig for this. Wouldn't the above be good enough?

It depends on your standards, not the quality of the mitre gauge.

As the section on mitre joints in a few books shows, some people would never accept a mitre cut for a picture frame straight from the saw (any saw) but would always refine it. In the home workshop this is generally done using a mitre shooting board. Here's a pic of one from a previous Answer in case you're not familiar:

Basic mitre shooting board

Source: Wood Magazine

In addition to giving a superbly smooth surface to the cut face (important for the best glue joint, although mitres should nearly always be reinforced in some way regardless) this allows you to sneak up on exact lengths in a way that no saw will allow — hundredths of a millimetre/a few thousandths of an inch at a time. It also guarantees your mitres are at exactly 45° if you build it right, each and every time.

Graphus
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  • I use pretty exactly this setup to plane a 45 degree mitre on 1" square oak for a picture frame. My problem is, that the piece tends to get drawn to the plane, no matter how hard I hold on to it. Do you have any advice on this? – Elbonian Feb 03 '21 at 21:56
  • @Elbonian, not sure what you mean by "drawn to the plane". If it's slipping during the planing you could try lining the 45° jig surface with sandpaper, this is a common addition to jigs to reduce slippage during a sawing or planing operation. A word of caution though, by making that surface less slippy it makes a shooting board much harder to use since it's much more difficult to shift the workpiece along incrementally for each planing pass. But how's your sharpening? If your honing could perhaps do with some improvement I'd look at that first. – Graphus Feb 04 '21 at 06:21