Grafting tomatoes

You can graft aubergine and peppers onto tomatoes and some people have grafted a tomato onto a potato but that would need to use a different technique. I think another method is to half cut through both plants when they are a bit bigger than i do it. then join them together and when the join heals, cut off the unwanted top and bottom. A nursery I visited earlier this year was selling grafted plants like that. A problem with that method can be that the 2 plants grow at different speeds before it heals so the graft pulls apart.
There are a few YouTube videos on grafting.