I have a 5" post vise that I need to mount. The post is a 6×6 sunk 3+ feet into the ground. Also does it need a plate under it or something like that? How would YOU mount it???? ( without a welder)

Thanks in advance, Hux. 

I'd put a plate under the foot with a hole drilled in it to secure it. 

The vise is missing the mount bracket and spring. There are a couple options. #1, you could forge the mount bracket and spring and mount it up. #2, you could get metal strapping or flat stock and make a U around the rear upright then lag bolt it to the beam. 

#1 would be more secure and functional. There are a couple types of brackets that they used. It doesn't have to be real fancy. 

Tho, you could also make a spring and incorperate the strapping to hold it. 

 #2a: make such brackets from flat stock and attach to post with U-bolts. This can also hold the spring.

(NB: This was in-progress, before the bracket got trimmed back and its sharp corners rounded. Another bracket got added to engage the lower U-bolt.)

My local farm supply store had u-bolts for mounting leaf springs to axles.  Fine thread so they don't back off.  It has worked well for me and the price was cheap enough.  Use the u-bolt to trap your new spring.  

Take a piece of angle iron, hefty with unequal legs is best. drill holes in the short leg of the angle iron for a U Bolt to go around vise shaft---I get unplated ones at the scrap yard and forge to square and fit to the shaft.   Drill holes in the long leg for lag bolts for the post.

What you get is very much like the mounting bracket Columbian Postvises used..

Definitely put a slab of steel under the acord to keep it from being driven into the ground shifting the vise downward.

I made this U-clamp for a vise out of scrap piece of 1/2 inch plate and 1/2 inch all thread welded together.

Definitely put some sort of a base under the post.  The whole purpose of a post vice is to transmit shock and impact down the post to the ground.  If you do not set it up for the base to accept the impact you might as well just have a machinist's vice mounted on a bench.

Also, in your mounting you will want to consider the height of the jaws of the vice.  I was told long ago that the jaws of a vice should be at the level of your elbow so that you can file on something held in the vice with your forearm parallel to the ground.  I have always used that procedure but it has seemed to me if I am hammering on something hot in the vice elbow level seems a bit high.  Others can comment on how high or low is the ideal for a post vice.

"By hammer and hand all arts do stand."

No; a machinists vise will shatter under the impacts a post vise will shrug off---even if it's being driven down into the ground stressing the mounting bracket. (Unless it's one of the crazy expensive malleable iron machinist vises...)

Thanks for the input. Here's what I used: I flattened some pipe and drilled a hole near the ends on the lower one. A spike was driven through them. The top is just hooked over and that's it. The spring is a piece off metal that was already bent so I just stuck it in.

The moral of the story: there's no need to spend hours looking for a way to do something when you can go out and take an hour to do it.  *The spring took half a minute;)*

Pretty innovative mount. I would drill the top band and anchor it with lag bolts. You will probably find without them any sideways hammering could pop the band loose at the most inopportune time.

Pretty slick, I like it.  I agree the top band needs to be anchored to the post or it's likely to slip as said already. If the vise slips up and down a wedge driven between the top band and spring will anchor it solid.

Good blacksmitherly job.

Frosty The Lucky.