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Ok, I'm bored so I'll say waaaay more on this subject than anyone wants
Most of these things used crowned pulleys because they do track the belt
AND they compensate for the fact that the shafting is usually far out of
alignment. The greater the crown, the more it compensates for
tracking/alignment problems and the more it chews up the belt over time.
Using a crowned pulley on belting causes a problem called an "approach
bulge". This bulge eventually causes the belt to wear out and track
poorly. The trick is to get as LITTLE crown as possible to avoid the
problem, and still be able to track.
Tracking is also a function of belt quality. Crappy quality belting
will always drive you nuts. It also sands far worse than good
commercial quality belting. the first time I used top quality sanding
belting I was flaberghasted at the extended life and fact that it
continued cutting almost like new throughout that life. At that time I
had only used "off the shelf brands from the home center (hobby stuff)
and ordered a box of "ends and pieces" from "the sanding
catalog"(division of Klingspor abrasives, I believe). These were ends
from fabricating industrial belts. Worth every penny to get the good stuff.
Anyway, back to my ramble to kill a little more time. Assuming that the
belting is straight and the pulleys are in perfect alignment, the
tracking errors that are seen are generally caused by the outer 20% of
the belting. That is, the center of the belt will run true and the
edges are where the tracking errors come from. To this end, a pulley
called a "Narrow Bodied Roll" is often used. A narrow bodied roll is a
pulley that is perfectly flat over the center 60% of the belt width,
with the edges turned slightly smaller in diameter under the outer 20%
of the belt width on each side. The diameter that is turned down is
only smaller by 1/5 of the thickness of the belting. What this does is
relieve the pressure under the edges that track poorly so they have less
of an effect on tracking.
One really great style of pulley for tracking with no problems was
developed by US steel. This pulley is called a Lorrig Type II.
Essentially, this is a lagged pulley where small grooves are cut into
the lagging at an angle toward the middle of the pulley. When the
rubber lagging compresses slightly under the belt, the flexation of the
rubber pushes the belt toward the center, causing positive tracking.
These things were VERY good. Pulleys cold be waaaay out of alignment
and still track the belting. The reason these never came into common
use is that they are more costly to make and US steel wanted a little
too much to license their patents.
Back to the original question.
Don't crown the pulley, taper it. Taper should be VERY small. The
smaller, the better. However, if the shafting is out of alignment or
the framework will flex under load and cause misalignment, the taper
needs to be increased. 1 degree taper would probably be a good start.
If you can get away with it, only the drive pulley should be tapered.
This pulley exerts the greatest force on tracking so is where all the
tracking needs to be done. The others should be flat if possible.
Often, because the drive needs to be lagged and rubber lagging is hard
to taper, it is left flat and tracking is done on the steel pulleys
instead. it depends on your machine.
Don't try and overcompensate for bad alignment by using extra taper.
Put your time into alignment via the use of good quality bearings in
the idlers etc. If it still won't track well, then go back and increase
Ok, I've rambled and killed enough time. I guess I should actually work.
Stan Schaefer wrote:
<pre wrap="">I picked up a new 1x42 belt grinder today and it needs a little
It is heavy cast iron and runs smooth except for the tracking of the belt.
On close inspection it has three plastic wheels for the belt to ride on.
I intend to machine up three new wheels but need assistance in the
The present wheels are all 31/2" in diameter by an inch across.
How should I finish the surface of the new wheels?
I presume I have to crown them all and should the edges be radiused or
I intend to use aluminum.
All suggestions appreciated.