Also to check your vinyl. Not all vinyl is perfect, If your making large orders like myself, you want to see the entire 8 ft or so before you cut it. You will find over the years, there are imperfections in vinyl or big sections of mottle. (This happens when vinyl rolls are tight.) Easier to see on dark colors. You have a chance to see those areas when pre feeding, and can cut those sections off of the vinyl roll and save them for smaller designs. You wouldn't want to cut a 8 ft design then see about 4 ft into the design it has a 1 inch section of mottle all the way across 24 or 30" wide roll. or a run in calendered vinyl. dimples,in vinyl. I cut up to 16 ft..So i prefeed the whole 16 ft. I do have a media basket. You could see if something is stuck on your grit roller, as it will make marks under your backing and show thru to the front when prefeeding.
With Graphtecs, the rollers make a nice little track in the vinyl to follow tracking, back and forth. This is why there is an actual prefeeding feature on the Graphtecs.