AusBonsai

I bought my first two Japanese maples back in November one is just a standard Acer palmatum and the other is a Sango Kaku.

When I bought them they looked pretty much as they do now, just kinda like long twigs haha. However, they are growing so tall now that when there is a bit of wind they tend to move quite a lot so I was wondering if now would be a good time to prune them back a bit?

I am still not sure what kind of design I want to go for with them but I am just a bit unsure whether I should prune them back a bit now or wait another year so they can get some more growth and then I can prune them back with more of a design in mind. Pruning them now would just be to make them a bit smaller so they dont get damaged by the wind.

Yes cutting them in half shouldn't be a problem.

You can certainly prune JM any time through summer. With good feed and water regrowth is usually pretty rapid so you actually lose very little trunk growth.
They generally shoot new growth close to the cuts so pruning high will not usually give any more or better options for shape. Chopping lower in winter will usually give you better placed new shoots the following year that can be better for design. I generally do a series of grow and chops over a number of years with most species before really looking at any style or design.

I agree with Shibui. When I have maples at this stage I cut everything to the lowest possible shoot (leaving a stub, of course, so that the dying back doesn't kill the dormant bud you want to shoot). They grow back readily, but with more branches than before the cuts. You can do this for multiple years. This increases your options when you come to do some proper design work down the track.

Thanks heaps for all the help.
I didn't want to do any damage by cutting too much in summer but if making some big chops is standard for maples then I will definitely cut it back quite a bit to get some new growth.

If it were mine i would get it grow for the remainder of the growing season and then cut it back leaving about a 6 inch stub at the end of winter.
then i would try and encourage multiple branches to grow long from different areas to add size thickness and taper to the trunk.
it would much faster to have 4 branches growing from a chopped stub than just one big long branch with the added benefit of adding taper and smaller cuts in the future. Imagine one big long branch has to thicken along its entire length . where as a 6 inch stub with 4 branches coming off it would thicken faster and more efficiently. also a few years in the ground somewhere sheltered wouldn't hurt.

are any grafted?