I have an FMT Pro jig that I bought about 10 years ago. It's very precise, if used correctly, and there is an adjustment for the "FIT" of the tenon to the mortise that lets you change the relationship by just a few thousandths at a time, which most other versions of mortise and tenon jig cutting systems do not have. The "Super" version of this jig does the same thing as the Pro version, but it's made from steel stampings and not CNC machined aluminum. The manufacturing process to build the "Super" version is cheaper, but the dimensions of stamped parts are not quite as accurate.
Still, when using a friend's Super FMT, I found that it worked about the same as my FMT Pro jig. I suspect that users of either jig that did not get good results just didn't follow the instructions as well as they should have. Learning to use the jig is quite easy. Learning to use it well takes some time to wrap your head around the features of the jig, what it can do.
and how to best use it, takes some time. Those who buy cheap are usually the ones who don't read instructions well or not at all.
I found that my jig works very well when making "floating tenon" joints too, by making the tenon stock for this using my Unisaw, and then getting the tenon thickness just right using my DeWalt 735 planer. When making attached tenons you need to account for the added length of the part before cutting the tenons, and then get the router attached to the FMT at exactly the right depth ao the shoulders of the opposite ends of your work piece end up at exactly the right length. With floating tenons, all of the work pieces can be cut to the desired length and the router depth isn't as important. Cut a mortise in the right place in both pieces, then cut the floating tenon stock to the needed length and the project goes together with the right dimensions. There is no need to round the edges of the floating tenons. Just make them as wide as the flat sides of the mortise. Leave the 1/2 round ends of the mortise for excess glue space. The mortise and tenon joint strength comes from the quality of the flat sides of the mortise and the tenon, and the glue used to join them.
Charley
