Shaping Young Japanese Maples

I have been growing Japanese Maples that sprout in my yard. I want to experiment with shaping some of them by staking and tying and would like to know how long it might take for the stalks to take a new shape. I have a batch that are about 4 years old, quite small and still supple. If, for example, I have one that V's at the top and I want to pull the stalks in to a tight V, how long might it take for them to hold the shape?

I have never done this and am only guessing with my answer.
It sounds like you want the trees to grow into a shape that is ailien to them so to speak.

The one's you say look like growing into a V shape at the top and you wish to tighten this V, I would suggest you use a pair of ladies tights or nylon stockings as they are light, stretchy and gentle, use these to tie the branches into shape you require, you will need to leave these ties in place for several years but, they ties may need changes every year or so a) to keep infections at bay and b) to check see if the ties are needing tighting or not. It might be a good idea to use a piece of pipe insulating foam (type a plumber would use to insulate a pipe) this will act as a cushion to preven the ties dig into the bark, it will prevent the ties rubbing the bark as the wind blows in winter etc, and prevent the ties slipping should the wind be really strong.

Other things to try if these little trees are free from cost,
Get a round wooden dowleling rod, place this into the soil like a garden cane, cover with the plumbers round pipe insulating foam for the same reasons as before, gently try to wind the trunk around the doweling ? covered in foam, tie (with ladies tights again, sorry) and as the trunk grows, keep winding this around, (think spiral/ coil shape trunk as end result) this is a method often used for making standard fuchsias and other tender plants like those, the whole idea for you is to try different things to see how they grow, I have seen (never tried myself) three plants / young trees grown side by side and as the stems / trunks grow taller when still supple, they are pleated and tied as they grow, after about ten years the support cane .stout stick, is removed and the pleated stems look absolutely wonderful but you would need to look on any form of changing the form / shape, etc of any tree or plant that has the natural habbit of upright shape/ growing, but, with a lot of patience it can be done, it's a bit like Bonsi in a way, but I'm referring to the time it takes, what I do know is the younger and more supple the plant material is when you start, the better but dont over stretch the ties, or make them too tight all in one go or you end up, i did the coil shape over three years with a standard Fuchsia about 10 years ago and it was going so well but, the deer that share our garden decided to have a rut fight beside my greenhouse and they wrecked my Fuchsia and many other plants, the joys of living in the countryside, Good luck and lets know how you get on over time, pictures before and after ha, ha, ha.
WeeNel.

Thanks for the thoughtful reply - lots of good tips. My first little experiment this spring was to straighten one of the maples which had just one long stem that was growing in a pronounced arch. When I straightened it up and attached it to a support, it was completely flat, and looked like a good candidate for espalier. Now, after just a couple of weeks, the leaves are realigning with the sun and it's becoming more three dimensional, but is now upright. I really should get the camera out and take some before and after shots. I was ready to get rid of all the trees this year (I have about 80), but now I'm sparked to keep them and see what I can do with them. Yard sale in a couple of weeks, so the nicer ones will sell and I'll be left with the "interesting" ones for exprimenting. Thanks again for the advice.