Fucking Machine - Forced Orgasms

Last week I teased about tying Mistress up.  She commented that she might consider it if I used the fucking machine on her.  That has had my mind spinning all week.  I think about strapping her down to our cross so she can't move her legs or hips.  I would position the machine and start slowly and let it build up until she had an orgasm, then I would turn it up a little faster.  She would try to get away immediately after orgasm but would quickly melt into the waves of pleasure.  I would use the hitachi on her clit and nipples to driver her even more crazy.  I also imagine doing it in our bed.  I would have her legs positioned through the metal part of the foot board so her legs couldn't close.  Here are some images that remind me of what I want to do to her.