Does a leg vice have to have a plate under its foot to support it or can it just be put on the ground? If it does need a plate to support it what would an ideal size be?

I am mounting my vice on a gum pole cemented into the floor and need to know if I should cement the plate in as well.

Bolt a clip to the pole with a hole in it to receive the leg. It wil save you some work and cement.

I recommend a plate so that forging force is distributed into a larger area. Otherwise you can drive the post deeper into the ground or chip/crack your concreat floor. I use a 6X6 inch square plate 1" thick to accomodate the post on a typical vice.
I hope this helps you.....

You do need something to absorb the shock on the leg and not transfer it to the mounting bracket.

 

For my portable vise I use an old hand  tamper plate about 8" square.  For my heavy duty shop postvise I have an old grader blade that is about 18" wide and 4' long and has nice sized holes in it to fit the vise leg acorn.

 

The "Ideal" one would be a slab of nickle steel about 20'x20' and 6 inches thick; though some will claim that 60'x60' is better...

 

Generally folks use whatever they have on hand in their scrap pile

I have a vise that is in daly professional use that has a simple bracket bolted to the mounting post it is made from 1 by 1/2". I often hammer on it with a 3 lb hammer and it is quite solid. It is only 4.5" vise. No need to build a battle ship.

Could I sink another gum pole directly in front of my original one like this?

Like you say Im trying to use whatever I have lying around and I don't have a plate that big.

 

ps. What do you think of my paint skills ha ha.

Bolt the two poles together so they cant move apart.

Here it is!! all set up and ready to be concreted in.

This is to show the size of this vice.

And here is the plot of land I cleared out today. (My brother in the background)

Another of my brother. This is about as much work as he did the whole time he was "helping" me 

Looks like that soil has a good clay content so cement might not be necessary if you tamp it good.  How is gum wood in terms of rot?

 

And don't fret, I have a brother that's about as helpful.  You get used to it.

Ha ha, this soil has no clay in it at all, just soil and a ton of rocks that are harder than hulks forehead. Had to beat them into submission with a steel pipe and a 9lb sledge to get the hole deep enough. The poles I have used are treated with special sealants so will last in excess of 50 years at leas before they start to deteriorate. Also I will be coating them in motor oil from time to time.

I use a small plate- an offcut about the sisize of a playing card, I welded about half an inch of heavy pipe that the toe actually stands in. The plate is anchored into my concrete floor with a couple of rawlbolts.

Well here is the finished product.

And here is what my shop looks like so far.