donkey ear for mitered boxes

There’s a conception that ‘Donkey’s Ears’ will true a hand-sawn mitred edge with the exactness of a well-adjusted shooting board. In my experience it probably won’t. They look the part but don’t do what you are thinking, otherwise every workshop would have them in a prominent spot.

Made from wood, there is often an amount of play within the clamping mechanism, so in reality, consider it an angled vice – something to hold your work at something close to 45 defrees.
That’s my experience of them.

Small pieces are best trued up on a shooting board. Larger pieces respond as well and as quickly, trimming to an accurate line with a sharp set of paring chisels and a good block plane. For final top-notch mitres, you can’t beat precise hand work with sharp tools.

If you have hundreds to do, a good quality chop-saw is the way to go.

Good luck.

Searching about, I recalled that Paul Sellers featured making a Shooting Board.

Here’s a link from 8 years ago: https://woodworkingmasterclasses.com/videos/shooting-board/

Spending some time making one of these will probably do what you want.
It’s important to use either good quality ply or very well seasoned wood that is stable because you don’t want any unpleasant twists if there’s a change in humidity – also to spend some time getting the angles exactly right. Coupled with a keen plane iron that is set at exactly 90 degrees to the edge this will produce exact mitres from the plane.

Good luck with it.