Rob,
I have a question about the drive wheel, all that I've seen have always been aluminum, machined to shape, I've never seen a contact wheel used as the drive wheel, so I'm ASSUMING there is a reason they aren't used for that purpose, my question is why couldn't a contact wheel be used for that purpose?
I'm not saying it couldn't be done. Matter of fact, it has been done, but there are some considerations- see below.
One of the largest considerations when attempting to use a contact wheel as a drive wheel is that of solidly coupling it to the driveshaft.
Most contact wheels popular for our applications are designed to have a bearing installed for free-spinning capability around a shaft, whereas an actual drive wheel will have a means of solidly affixing itself to the driveshaft in order to transmit the power to the belt (usually via keyway and grubscrew).
Another consideration is affected by many factors, including motor torque, speed, wheel design, and the counteracting pressures.
By design, a contact wheel has a solid wheel encased in a flexible outer material, be it rubber or polyurethane. When rotating speed is applied, centrifugal force causes these materials to want to expand slightly away from the solid wheel, which is not ideal for a drive application.
Depending on the factors above, a point
could be reached where the outer part of the wheel will want to slip on the inner portion, and the wheel no longer effectively transmits full power from the driveshaft to the belt.
When such a wheel is simply used as an idler to guide the belt, these concerns are of little, if any, detriment. But when used to actually drive the belt, we need to at least consider it.
That's the "theory" anyways, and if I were designing these machines, I would certainly take it into consideration.
Although it may only be theory for our application, there are real-world cases of the effect.
My first real experience with this problem was when drag racing in my younger days. "Slicks" are used for traction, and if you look at them at rest, they appear "flat". But as the vehicle picks up speed, the tire expands. Look at a picture of one taking off at the starting line compared to one halfway down the track.
That illustrates the expansion concept.
To visualize the slippage concept, take a look at the methods racers use to hold the tire onto the wheel. Screws will be installed around the perimeter of the wheel, mechanically affixing the tire to the wheel.
Of course, this exemplifies more extreme conditions. Will any of it matter for something like our grinders? I don't know. But the goal is to transmit power, and any type of machinery will have a weak link.
For some, the weak link is the motor (stalling out).
For others, it's belt tension, meaning the belt slips on the drive wheel due to inadequate tension.
I know Wayne Coe has mentioned that sometimes people have actually applied enough pressure to tilt the machine if it is not held down (illustrating motor power requirements). In this case, all the "links" are strong enough that the foundation (machine not being bolted down) becomes the weak link.
So if you use a contact wheel as the drive wheel, it becomes another "link". Whether it makes a difference or not is going to depend on all the other variables (motor torque, speed, belt tension, wheel construction, etc.).
But first you have to have a design that solidly couples to the driveshaft.
An example is the Grizzly, where the drive wheel can also function as a contact wheel. But I find it interesting that such designs are nearly always a single speed, allowing expansion of the two-piece wheel to be consistent. It would be interesting to see if any problems become evident if speeds were increased on those designs. If speeds vary, so will centrifugal forces, which is bound to have an effect on wheel expansion.
Again, I don't know. I don't own such a design, nor have I used one. Surely someone out there has modified theirs and can report on the results.
In the end, it all depends on many variables, especially wheel construction itself. Exactly how the outer contact surface is affixed to the inner portion of the wheel is paramount, and there are lots of ways to do this.
When I was younger (fresh out of high school), I got a job at Mid-States Rubber Products. You would be surprised how much back-and-forth banter went on between "our" engineers and "theirs" (the customers).
Lots of different ways to skin the proverbial cat (please note the use of the word
proverbial), but my long-winded explanation at least lets you know the obstacles. Maybe such obstacles are why we mostly see a solid one-piece drive wheel.
Perhaps contacting someone like Rob Frink (Beaumont Metal Works) can net you more detailed explanations.
Good Luck,
Rob
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