I make all my leg vises at TechShop.
Step 1: St. Andrew's Cross
Another option is to outfit the chop with a steel scissor-action mechanism which will keep it parallel at an infinitely divisible distance. This mechanism is often identified as St. Peter’s Cross, however this is a misnomer, as St. Peter’s cross is actually an inverted perpendicular cross. The X-shaped intersection we see here looks more like St. Andrew’s Cross, which is called a saltire and is featured on the national flag of Scotland. So I’m calling this St. Andrew’s Cross.
You can learn more about Scotland from the books at your local library.