Which wheel for idler wheel?

Hey guys, I am about to order my wheels from sunray.
I am going with a 4" drive wheel, directly on the motor. It'll mean I'll have to work fixed speed for now, but at least I can get started without having to worry about getting a decent pulley setup.

I am also getting the grinding wheels from them (2" wide so they are compatible with the same belts as KMG).
But what do I use for the 3d wheel (the idler wheel)

Another 2" or 3" polyurethane idler wheel, and then crowning it with a bit of sandpaper?

No sandpaper needed Bruno. You can make enough crown with a center strip of good tape like electrical tape or the strapping tape type that has the fiberglass strips embedded in it. Use some one inch wide stuff and put a couple turns around the very center of the wheel. If that does not seem to work well keep adding tape until the belt self centers. The tendency is for the belt to seek out the highest point. Even some wheels that are already crowned may need a little tape if the angle isn't enough.

More important is a good setup for the tracking adjustment so you keep the belt in the center of your contact wheels. I checked my Bader this AM, the idler wheel and the drive wheel are both 2.5 inches (6.5 cm) wide. This gives some wiggle room for the belt to move side to side when the tracking adjustment centers on the contact wheel.

Hope this helps.

Perfect question, perfect answer, perfect timing, since I just finished welding up an adapter to my grinder to incorporate a 3rd wheel

What eexactly do you mean with tracking ajustment? Set screws?

I use a wheel like this:

Tracking / tension Wheel 3 1/2 by 2 1/2 with 1/2 bore and bea No Weld Grinder Sander - 2x72 belt sander grinder Grinder part

for idler/tracking

Good link Undream. This next site gives you an example of one type of the adjustment system. CNCCookbook: Belt Grinder Ideas

There are several good ways to do this, but the above site has some really good pictured examples of one kind of the moving parts. What is necessary is a simple two axis lever so that slight changes to the idler wheel axel can be made. This should allow the belt to drift slightly to one side or the other as needed to keep it centered on the main contact wheel where the metal removal occurs.

Despite modern manufacturing and essential sameness between belts, there are slight individual variations in belts that can occur. Sometimes the operator forgets to dump the tension in the grinder and the belt takes a "set" from the two or three points of the grinder. Then when at speed, those variations or wobbles can move the belt around significantly. If there isn't any way to keep the belt on center it can be a real PITA trying to use only half the belt, or the belt keeps running sideways off the contact wheel, or it moves side to side when you put a load on it trying to remove metal.

And, there are few things more exciting to the grinderperson, than having a 24 or 36 grit, 72 inch or longer belt come off the grinder at 5,000 surface feet per minute and wrap around your head and shoulders. It only takes once to prove why a hat and safety glasses or helmet and faceshield and gloves and apron are really good ideas. Or you can simply marvel that some crazy idiot would even approach a tool like that near enough to get some work done and make a razor shaped object. ;) The really nasty cuts are from the plastic belts with the teeny micron grit when you just barely bump up against the edge of the belt with bare skin. Like a paper cut but abrasive and really moving fast.

Sorry, you guys all probably thought the buffer was bad enough.... :)

I use the same tracking wheel that Brad posted.
As for adjusting it, I went pretty straight forward. The pic is pretty self explanatory but basically a hole cut out on one side and nut welded to the other. The adjustment screw pushes the plat/wheel out for adjustment.