Here are a few comments about wheels for heavy power tools:
* Good quality mobile bases and similar rolling solutions are not cheap.
* There can be significant differences between mobile bases in ease of use, ability to roll over cracks, bumps, etc. without issues. Some bases "glide", others are far less smooth.
* Big wheels make a big difference in ease of use over small wheels.
* Some bases have three wheels, others have four. I do not like or recommend three-wheel bases, although it may be the only choice if you want the integrated wheels that are designed to attach directly to the tool. My old bandsaw came with a low, three-wheel, flat rolling frame designed to match the feet of the bandsaw. It must have been made at the same time, the early 1950s. Bandsaws are tall and top-heavy. The bandsaw with its all metal base and three tiny metal wheels is scary to move, especially with that single tiny metal wheel in the front.
* Look at how the tool will rotate into position. Some bases allow the tool to be rotated in place. Other bases work like shopping carts, with a pair of fixed wheels and one or more rotating wheels. In a tight space, they are much more difficult to maneuver.
* Some mobile bases allow to the tool to rest directly on the floor when ready to use, where the wheels are not supporting the tool. This is the best design.
* If you want wheels where the tool rests directly on the floor, think about how you will lower and raise the tool. If the wheels are raised and lowered independently, will it be a problem with the tool tipping back and forth? I have a set of workbench casters and noticed that a lot of people tie two casters together with a single foot-bar to raise and lower one side of the workbench without tipping.
* Sometimes a mobile base will lower feet to the floor in the front, but rest on its wheels in the back. It is not as good as when the entire tool rests on the floor, but it seems okay to me.
* Other mobile bases leave the tool on the caster wheels while in use. Now you have the issue of the wheels wiggling and vibrating with the power tool when it runs.
* Most casters lock the wheel, but not the swivel. If your tool will rest on its wheels during operation, consider "Total Lock" casters that lock both the wheel and the swivel. I have found them only at Rockler, but there may be other sources.
* Many tools have mobile bases available from the manufacturer. Sometimes they are generic mobile bases from outside the company that happen to fit the tool. They are painted and branded to look like they were designed together. Other mobile solutions are integrated into the tool itself. I have seen some that are really really good, and others that are really really bad. I know a few people who bought a better generic mobile base rather than buying the manufacturer's less capable integrated solution.
* A few tools have lower doors. I am thinking mostly about bandsaws, but some table saws have low access panels, and there are probably other tools that fit the description. Be sure that the base won't interfere with the lower door opening and closing.
* You can make your own mobile bases out of metal or wood or a combination of the two. Some bases provide the metal parts and you supply the wood frame. Don't skimp, use solid hardwood on those.
* You may have to reinforce your tool to make it mobile. Sheet metal can be thick or thin.
Example: My Delta lathe came with a stand whose bottom is made of two square steel tubes on either side, perpendicular to the lathe. The ends of each tube have a welded 1/2 inch nut on the inside, designed so you can screw in threaded casters. I bought Total Lock casters at Rockler, and screwed them in. Done, right? Nope. The top of the casters where the threaded post comes out has a welded nut on top, making the surface area of the connection between the caster and the stand small, instead of supporting the caster by its bearing race. The thin steel of the square tubes bent when the casters rolled over pillow top pavers. When the metal in the square tubes bent, it made the casters point in skewed directions so the lathe could not roll. I fixed it by installing flat Simpson ties inside the base tubes to stiffen them, and provided drilled wood supports so that the weight of the lathe was on the bearing races and not the small nuts on top of the casters.
Example of a Superb Mobile Base:
In my opinion, the standard from which all other mobile bases should be measured is SawStop's Industrial Mobile Base for their industrial (ICS) and professional (PCS) cabinet table saws. It is not the same as their "PCS Integrated Mobile Base." The Industrial Mobile Base has a "cradle" design with a hydraulic lift. You pump the foot pedal a few times to raise the saw. Another pedal lowers the saw to the floor. It has four large swiveling wheels and allows full rotation in place. Quoting from Trent Davis' blog, the SawStop Industrial Mobile Base, "Will cause you to despise all other mobile bases you ever use." He's right.