Scrolling overhead projector transparencies - experiences?

Someone here is bound to have some experience - I can’t find any commentary elsewhere…

I sometimes teach in a classroom with an overhead projector and a stack of blank 8-1/2 x 11 transparencies. After each class I laboriously clean off each film with water, but it still makes a mess of me and everything around me.

Plus, the films are smaller than the projector panel, so a lot of “area” gets wasted.

It occured to me that an improvement would be to mount a roll of full-width film on the front of the projector and have it feed a take-up reel at the back, then just swab it with a sponge when the roll runs out and you’re rewinding.

I went to the 3M (projector manufacturer) web site and what do you know, they had exactly what I was looking for as an attachment for their machines.

Are they the cat’s pajamas? Anyone know?

Liquid from the sponge can inadvertantly get rolled up in with the just cleaned film. It won’t evaporate in there. This can cause ickiness.

Wow. I haven’t seen roll-fed OH projector film in 25 years. More accurately, I haven’t seen the stuff actually used in about 30 years, but our projectors had the brackets for it.

You’d need to re-wind it back in screen-sized bits - wash and dry, roll it in, wash and dry, roll it in, lather, rinse, repeat.

You may have better results with dry-erase pens, as they’d just need scrubbing off with a towel or a whiteboard eraser as you rewind the roll.

This is exactly what was used in all the lecture halls at my alma mater. Even the smallest classrooms had a pair of overhead projectors, while the largest had four of them projected on large screens. I think the professors used grease pencils and would roll the transparency during the lecture. (We used to wonder who had the job of cleaning all of those rolls.)

Yeah, I have to get the sheet film bone dry before I can stack it. I figured I could rig up a multi-fingered squeegee with three or four dry towels after a wet leading edge, but I’m worried that it really also needs a few moments to air dry, as gotpasswords indicates.

The rolls have 100 feet of film on them, so I’m hoping it’s practical to use the whole roll before the clean/rewind step, but I’m concerned that the wet-erase marker ink might start to bond if it sits too long uncleaned.

I’ll have to experiment with dry-erase markers and grease pencils.

I used one and left it until the end of the roll and didn’t have a problem with it getting messed up.

I used to have my students clean it but they were in 7th grade and thought it was fun for some reason. I don’t know what age you teach though.