Now you need to look for one that is smaller and another that is larger. Then you can start filling in-between for a set of five. Then you will need to build a special bench just for the post vises and some other antique tools. Well, then you might as well build a bigger shop ....
Seriously, one great way to utilize a post vise is to make it a semi-portable unit. Take a 36" piece of 4X4" square tube*** and weld a round or square foot plate to the bottom. The plate can be any size around 12" to 18". Weld a 12" piece of 3/4" pipe*** about 6" from the center post. It should stick straight up parallel to the center post.
Put an old car/truck rubber tire on some sandy soil and settle it level so the soil is even with the bottom side rim. Put the post and foot plate in, centered in the tire. Adjust everything so the tire is seated level in the sandy soil and the post is vertical. Pour it full of concrete and let it set. Make sure the post stays vertical.
Once set, cut off the 3/4" pipe about 1/2" above the concrete. This will make the foot spot for the post vise. ***
Place your post vise on that foot and measure where the mounting plate meets the center post. Mark that spot.
Get a piece of 1/2" or heavier plate about 6X6" *** and mark the thickness below the height mark you made.
Double check the fitting of the post vise and cut the post off there and set the 6X6" plate on top. Figure out how much of it needs to stick out to mount the post vise vertical and weld it in place there. A couple 90° welding magnets make this an easy task. You can tack it in with MIG, but weld it up solid with a stick welder.
Drill the top of the plate to fit the mounting holes for the leg vise and bolt it on.
You now have a semi-movable post vise setup with plenty of mass to allow working steel.
***
Do a sketch first using the measurements of your post vise to decide how long the post needs to be. It is best to have extra length and cut it off exactly where needed after the tire is poured. It also can be anything from 2" pipe to a train axle. As long as it is vertical steel that you can cut and weld on.
The 3/4" pipe should fit a post vise leg foot just right. If not, pick whatever size fits your post vise or use a piece of 1" rod and cut it off almost flush with the concrete. Weld a 3/4" nut or whatever fits your post vise foot on the rod.
The top plate can be anything from 1/4" to 1" and any L/W you want to make a top table to set things on. It is positioned to allow the post vise plate to bolt on and the rest is a work area. You can hammer things on the flat table if you use 1/2" or thicker steel.
