The wheels are as follows:
- 10" - probably the best all-around for hollow grinding. The easiest way to get it is to order one from Grizzly. It has to be modified (bored out for BB).
http://www.amazon.com/Grizzly-G9242-Aluminum-Rubber-Wheel/dp/B0000DCZX1
- driving and tracking wheels - KMG (tracking comes crowned, real nice) or DIY
http://www.beaumontmetalworks.com/
click on "Contact wheels" and "Drive Wheels" . If you order drive wheel online, make sure the hole and the key way match the motor's shaft
- the 4" and 5" contact (you can also turn it into tracking):
http://surpluscenter.com/item.asp?UID=2008062910322602&item=1-2875&catname=wheels
The poly on these machines beautifully . Removal of stock needle bearings is a 4 second affair, they come right out.
- I am not a fan of idlers - as you can see from the platen. I recommend to have a 2" and 3" contact wheels instead incorporated into the platen design. KMG or Sunray or DIY .
If you build your own contacts or adopt/modify grizzly and surpluscenter ones, you'll need to bore out the stock center holes to accept 2 of 1/2 ID BBs. That requires a mill or a lathe. For example, to bore out grizzly's 10" wheel, one's lathe might not be big enough to spin 10" over the bed - so you bore it on a mill. YMMV . If you don't have the machinery reqd, befriend a friendly machinist (6 pack ?) or buy premade ones from your favorite supplier. KMG sells the whole range of contact wheels and at smaller sizes they are rather affordable.
There's also Sunray:
http://www.sunray-inc.com/detailwheels.aspx?ID=112
http://www.sunray-inc.com/detailwheels.aspx?ID=226
http://www.sunray-inc.com/detailwheels.aspx?ID=398
driver:
http://www.sunray-inc.com/detailwheelsdrive.aspx?ID=113
They can do a small OD too, just ask. Go with harder rubber and 1/2 ID ball bearings.
The OD of the driving pulley depends on motor's RPMs. For a 3600 RPM motor a 4" OD driver is a good choice - giving you top SFPM of just under 4000, you won't need to go any faster than that
Now, the most expensive contact wheel is the 12" . I got lucky and bought some flat belt pulleys from surpluscenter when they had them - dirt cheap. I just use some duct tape (many here frown upon it, but we _all _do know 7/8 of known Universe is held together with duct tape) .
But if you ever sell a knife or two, I'd invest the money into a 12" or 14" wheel - KMG has them.
Some people come up with a "curved" platen - that simulates having a 14" or even larger wheel.
And lastly, don't use idlers or contacts at too high of RPMs as you will kill the bearing.
For example, having a 1" OD contact going @ 4000 SFPMs is a really bad idea, you need to slow down.
Don't over-tighten the bearings (races) - you want remove all the play but still have bearings rotate freely.
