table saw-router combo mobile base design

[Andy Maldoror]

i bought a mig welder to build some mobile bases for my tools.
first one i need to do is a unisaw with router extension...it sits in a tight spot and i have to drag it out every time i use it.
http://img191.imageshack.us/img191/4033/tsrt.jpg

i just started welding and have done lots of practice welds, but that's it...so bear with me.
i was thinking of maybe using 3" tubing around the bottom with angle welded on the inside under the saw...the cabinet will sit on top of the tubing...something like this that chip lindley posted:
http://www.sawmillcreek.org/attachment.php?attachmentid=160206&d=1283483881
except i will need swivel casters on all points to move it in all directions. would i need larger casters than those under the saw?
can someone explain the general layout and parts i will need? for instance, do the support legs have to be adjustable? do the bolts help support the caster brackets through the whole tube in addition to welding them on?
i haven't priced materials yet...about how much might it cost to build something like this?
thanks,
andy

[Trent Shirley]

It's hard to tell from the picture but I think this is all angle iron rather than square tube except possibly for the center cross brace and the legs supporting the extension.
Your casters should be chosen based on the amount of load they will be holding so the ones under the saw might need to be stronger but not necessarily larger. The diameter of the wheel and the material used will alter the way it rolls so consider if you have a nice smooth floor or a bumpy one and go larger diameter for a rough floor.
You might want adjustable height for the extension end if you have an uneven floor and may end up with one caster not actually touching the floor when it is in the preferred position in your shop. If you want/need to level your table then adjustable casters would be needed as well, probably on all four corners.