Vacuum solder stencil jig remix

This is a ground-up remake of Max Scheffler's awesome solder stencil vacuum jig. I needed it to be a little larger, and while I was at it, made some structural changes for improved placement repeatability. 

Significant changes:

• increased area of PCB holder and added undercut for popping board out when done
• added collar for friction retention of springs
• changed lifter alignment pins from screws to M3x30 dowel pins for better repeatability
• added matching tapers to printed part interfaces for improved alignment
• added internal supports to vacuum chamber to prevent bowing from negative pressure
• added M3x5x4mm heatset insert pockets for fixing PCB holder to lid (longer life when swapping PCB holders) and for fixing stencil to lifter (to allow for repeated placement)
• changed vacuum adapter to screw on rather than friction fit

I find that with this jig I get sufficient alignment repeatability to stencil new boards without having to re-align the stencil, allowing me to use four M3 button head screws to fix the stencil to the lifter. 

As uploaded, it works perfectly for 190mm x 190mm stencils.

See it in action: https://imgur.com/a/DRmLaZt