This is a guide for cutting 45 degree miter joints in wood up to 2x4 inch (1.5x3.25 actual).  It uses toggle clamps to lock onto the wood thereby providing a 45 degree surface to guide a flush-cut pull saw.

The design is available on Onshape

I used 1/4-20x4 threaded rods and t-nuts but it is trivial to change that to whatever hardware you have.  The foot pads should be printed in TPU, everything else doesn't really matter.  The knob and foot pads just thread on without needing anything to lock them in place.  Very little force should be applied when the toggles are snapped in place.  They're just holding the guide in alignment and it sees practically no force pushing it out of alignment.  The toggles pivot on M4 x 24mm binding post screws.  Again, this can easily be changed to use, for example 4mm dowel pins or just screws by changing the size of the holes.

If anything asymmetric will be cut (such as a frame with a rabbet) it is a good idea to have a second mirrored version.

I found that this worked well after a little practice. The first two attempts were a little off but by the third all went well.  Although this is completely original, I did crib the pivot distances from Funi's design.