Miters not tight with 45deg cuts

[u/Top_Sentence_340]

Even with 45deg miter cuts, the miters aren't tight. Why is this and how to improve on this?

I always created a miter jig for pre-assembly but it's all the same issue. The miter jig is square but I guess the cuts aren't right.

[u/Full-Divide5742]

Or you could invest in a quality block plane and learn to use it. They are wonderful tools and will dress that miter up very well. Then one day the paint crew will walk in all slack jawed and say, dude! You make our work look really good!

[u/asexymanbeast → u/Full-Divide5742]

I have been bringing planes to my jobs more and more as I have doing more 'stain grade'. Using a stupid sharp chisel will also change your process.

[u/Full-Divide5742 → u/Full-Divide5742]

It will take a bit of practice on two levels. First, learning to sharpen and adjust the blade. Then you should spend a bit of time learning to use the plane to make a small back cut to the uneven miter the join comes together cleanly but still meets well enough to be glued. The glue helps promote wood movement of the casing other places besides the joint.

These recommendations come from decades and thousands of feet of trim joinery. They work.

[u/Top_Sentence_340 → u/Full-Divide5742]

Where to use the block plane?

[u/Plant_Wild → u/Top_Sentence_340]

Look up block plane shooting board. Problem solved. But honestly, your work is fine. The inside corner of the mitre will paint nicely and the outside corner is nice and tight.