After posting my Circular Knitting Machine (thing:6273014) I received several requests for a larger version, apparently to make hats and such. Here is a design for such a beast.. The OpenSCAD file gives you the opportunity to make any size you want (within reason). The accompanying .STL files are for a machine that should fit on a 220x220 build plate (I hope)
The central cylinder measures 194 mm diameter and holds 120 needles.
The machine is still bi-directional, however the yarn carrier does not relocate automatically anymore. You need to swap the yarn between the two carriers manually. I do not immediately see the need for this functionality while knitting hats, but it is there. If you do not need it you only have to print one yarn carrier and use it left- or right handed.

You can use the missing parts, like hand crank and knobs from the original design and the build method is similar.

CAVEAT: I have not built this machine myself, nor do I intend to build it at all. I also do not know if the size is adequate for any practical hat or beanie. You are on your own here...

Update: To make bi-directional use easier I added a yarn shuttle. You can mount that instead of the yarn posts. The shuttle screws on top with 2 M3 screws. The original guide slots into the shuttle as normal.
To use, pull the shuttle back and slide over, then forward. The threads tension keeps the shuttle into the recesses and should stay in place while knitting. (see third image )
I realized you may want to knit a "toe" on top of your hat :-)

Let me know if you require further modifications

Creality

CR-10S

No

No

0.2 mm layer height 0.4mm nozzle

20%