If you are cutting back beyond where the current seasons growth started, you won't get flowers and fruit, only growth.

What you need to do is only cut back in mid winter to within a couple of inches of the base of this years shoot leaving just three buds. This means that your vine will only get bigger by three inches each year and will flower and fruit too.

Select the main stems that will be the permanent framework and all subsequent growth from then on can be treated as above.

One important point, don't prune at all in early spring. The plant will just pump all the sugars and carbohydrates it has stored over winter in it's roots out of the newly cut ends as the sap rises and be either severely weakened or die. Only prune in mid winter.

Fractal - is it possible that this grapevine is an ornamental one? I have Vitis coignetiae and Vitis vinifera purpurea in my garden, purely for their beautiful leaves. They both produce tiny bunches of grapes, but not edible ones.

Maybe Wayne could post a photo of his in case it isn't a vine that will ever have usable grapes on it?

That is true. We will have to see if he does. :-)

Even ornamental ones as you know can be treated the same to restrict their growth of course. I await his reply...