I just received my first Graphic camera... a Crown Graphic 23. The camera came with a "23" Graphic 6x9 roll film back (knob wind). When I remove the ground glass, and secure the roll back, it seems to seat properly, but there is nothing stopping the entire back from sliding off the camera to the right. There is enough friction that it doesn't just fall off, but a nudge will push it pretty easily, potentially exposing my roll. Am I missing something here? It is a graflok back, btw.

Did you move the Graflok sliders down to hold the roll holder?

Correction: NOT DOWN

Move the bottom slidelock UP and the top slidelock down. You do this by sliding each slidelock to the RIGHT.

This question was also asked on apug.org and was answered there.

The OP put up images of his roll holder. It is a Graflex "23" -- so marked -- and was made to fit on a Graflex SLR with a Graflex back. That's why it doesn't have a ridge that engages the slot on the right side of a Graflok back.

The OP added to the general confusion by insisting he had a Graphic "23" but his images say otherwise.

And there are some Graphic cameras that the graflok sliders slide left to secure the accessory onto the back.

Yes, there are all kinds of ways of attaching a "23" graphic to cameras. I've got a Busch Pressman C with a "23" roll film holder. I'll post pictures of it soon. It has the slidelocks for a roll film holder but the problem is there's no way to attach the groundglass view back.

http://graflex.org/helpboard/viewtopic.php?t=6329

There are four configurations for the sidelocks. Slide-to-the-right to fasten the film holder is factory default, but you could change it to any of the other right-left/up-down configurations if you wanted to.

It sounds like the OP might have a problem with ridges.