I started out using regular box tape (2 inch shipping tape). The material that I have been machining is 3/4 inch oak.
I would vacuum any dust off of the surfaces and then use a plastic card to squeegee the tape tight competley on all 4 sides. This has been working very well although I knew that I would want to put a better system in place at some point.
I was surprised that I was not able to not find more posts about holddown options. There does seem to be many people using vacuum systems.
Here's a solution that I came up with recently thats working great for me. It works great for wood or a material that can be nailed into fairly easily.
-I made 2 side rails out of oak about a foot long ,3/4 inch high, and 1 1/4 inch wide.
- I then drilled pilot holes and inserted some decking screws long enough to leave the screw tips exposed on the other side (I used 1.5 inch screws and had quarter inch exposed tips). I also used a dremel to sharpen the screw tips very well after installing.
-The end bolts on the rails are counter sunk and attach to nuts in the slotted channels of the table.
I keep the left rail locked and then tap my work piece into the screw tips with a tack hammer. I then tap the second rail into the workpiece and tighten its end bolts.
I keep my router away from the screw tips by homing my x half an inch from the left rail and also make sure that the object I'm going to cut (its dimensions in my gcode file) do not come closer than a half an inch to my right rail.
Here are a couple pics: