Ask anyway.
I was cool with asking actors to work for nothing, they wanted to. I was cool with asking a cinematographer to work for free, in my case they wanted to get a feature under their belt. Similarly, but to a lesser extent the same goes for your effects team, costumer, and most anyone who has some creative input into the film. I didn’t ask anyone to be prop master or a dedicated continuity person, or drivers, or runners. Basically if it seemed like a task job rather than a creative job I assumed no one would want to show up and do it for nothing. By the time I was thinking about those tasks I was deep into pre-production, and as a writer/director/producer most every aspect of the film was tedious to me already, I couldn’t imagine someone giving up days to a tedious gig for no pay.
My thinking at the time was that with enough planning we could go without a prop master, or our script supervisor could pull double duty and keep an eye on continuity. And let me just say that was insane wishful thinking. At some point in a day on set your plans are going to change, most likely numerous times in a day, its just the nature of it. Weather forcing you to rearrange the shooting schedule, an actor needing wardrobe worked on, little things mean you shuffle things around. And then what? If you have someone tracking all the props you don’t have to rely on them being where they should be based on a plan you made a month before the shoot.
The oversight here, for me at least, is the notion that your making a film. Folks dig movies and are down to just hang around and watch it be made. If they have a job on set it makes them a participant rather than a spectator. Sure it’ll get boring for them, but everyone from the actors to P.A.s to the director will have a moment of boredom at some point or another. It is all ‘hurry up and wait’ remember.
Simply put if you don’t ask people to help you’re gonna be short handed. If you do ask you still will most likely be short handed, but probably less so. I personally got sort of lucky as I have a big family who all pitched in without me asking. They saved me and the production in a number of ways, too many to count actually. I’m eternally thankful for the help, but had I asked ahead of time I wouldn’t have had the amount of stress and concern I did going into the shoot. And if being thankful is all you can offer them, well then ask them and thank them if they lend a hand.