Miter Box with quick clamping system.
 

You just need: 

M8 threaded shaft

2 x nylon straps 20/30mm wide

2 x M8 nuts 

Optional some M8 spacers to protect the straps
 

Feel free to share any comment, thanks!

Demo:
https://youtube.com/shorts/_bNxrlp7j60?feature=share

Fully parametric model available on Onshape:
https://cad.onshape.com/documents/31bcd0ce9bd8dbfd1e879866/w/f64da36f92f3e52298c46afc/e/72b4b0be1f269191c28dd5fa?renderMode=0&uiState=663b8e1b1825c3633d4a318a

Standard printing settings should work just fine. Only advice is if you print in ABS, given the size, you need some tricks to avoid warping: Add large brims, keep bed temperature between 100-110 celsius, place the part as far back in the bed / enclosure as possible, use abs glue.