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.
Step 2: You Will Need:
Vise screw and nut
2" x 8" x 32" hardwood (for the chop)
36" of angle iron (8 gauge) or thicker
12" of 5/16" metal bar
Various nuts, washers, and spacers to fit
Basic woodworking tools (saw, router, chisels, drill)
Basic metalworking tools (metal saw, angle grinder, drill)
Step 3: Making the Cross
The bolt has to hold the two bars together but not under tension. I am using a stainless steel collar bolt with just the right thickness of washers to hold the bars in place without squeezing them.
I gave the bars a patina of iron oxide and a clear-coat to prevent rust. I will lubricate them with sewing machine oil.
Step 4: Prepping the Chop
Next the 5/16" through-hole is drilled for the pivot. I used a Forstner bit and a drill press for this to keep the hole as straight and perpendicular as possible.
Step 5: Prepping the Bench
It is important that the pins holding each of the bars are at the exact same height. Here they are placed 12 1/8" on center from the top of the bench.
Step 6: Assembly
In fig. 2 you can see it holding a large block of wood at the top edge while remaining parallel.
If your chop experiences any raking, despite all parts being true, you can place a strip of sheet metal in the bottom of one or both of the channels. This will widen the bottom half of the assembly and should compensate for raking that occurs under pressure. It's okay for the chop to be out of parallel when not clamping, but slight raking while being clamped will cause a noticeable decrease in holding power as there will be only an edge of contact with the work piece on one side.