Two sided routing accuracy is a direct product of your hold down accuracy. If your hold down is off by 2 or 3 thousands your route will be off. Most of what I do is in wood and so that is not that big of an issue, in your case that may make a big issue. I have used pins, adjustable stop blocks, etc,. The cutting pressure also has a direct bearing on how will your hold down methid will work routing two sided. Russ