How do you motivate collaborators to meet deadlines, when there is no financial incentives involved in their work?
Perhaps you are asking for more than can be delivered. The other person, I assume, has his own projects and deadlines and, perhaps, needs to put those first. 

Incentives can be other than financial, of course, but perhaps the incentives important to the other person are all directed toward making progress on work more important to them than to you. 

Trying to beat up on someone who has been valuable to you is a mistake, I think. Setting deadlines for someone who is neither your advisee nor your employee is likely to be fruitless. 

What incentive can you offer. The carrot, not the stick.