This hold-down toggle clamp is based on the model by Izzy Swan. Although there are several models of homemade toggle clamps on the net, this is by far, the most popular and besides you can download the plans for free. And the best part is that it works!
Once you have downloaded the plans (you can choose PDF format, among several others), all you need to do is to print them, cut the parts and glue them to the wood, then cut each part with a bandsaw or similar, and finally, assemble the pieces.
This is a video and plans of the hold-down toggle clamps at thinkwoodsworks (Izzy Swan’s page) (note: if the link doesn’t work, copy and paste the address): Free Plans
This is an update video by Izzy Swan:
Here you can download the free plans: https://www.dropbox.com/sh/dildgadtv6cat03/4U7aY4pA8z
And here is an explanation of how to assembly the pieces, by CNCnutz .