Find paper gap thermal printer 2844 i have 4x6

#1

I have thermal printer 2844 i have 4x6 paper and other sizes .
i need to find the CLEAR ( not BLACK) paper gap.
HELP !!!

i used
this is some of the items i think can help

https://www.ebay.com/sch/i.html?_from=R40&_nkw=Infrared+Reflective+Photoelectric+Switch+IR+&_sacat=0&_sop=15&rt=nc&LH_BIN=1

i need to feed 1-2 page a second or you tell me the speed

it is not stable ,