If you befriend a mechanic, he may lend you a small measuring tool
which they use (SHIM?) to adjust the engine, it is paper thin
pieces of metal moving up in scale to several mm, and you just
slide the measure along the roller from one side to the other,
leaving the left alone and adjusting only the right hand, this way
will ensure your rollers end up exactly the same height.
From an engineering aspect, this is NOT the way. When a rolling mill
is used, the pressure required to squeeze the metal being rolled is
transferred to the bearings at each end of the rollers. After a
period of use there will, inevitably, be some wear in the bearings,
making them slightly oval instead of round.
For the bottom roller this is not a real problem because it’s own
weight ensures that it settles with the gap above the roller axle.
The top roller is a different matter. When the gap between the
rollers is measured with a feeler gauge, or piece of shim moved
across them, it doesn’t lift the top roller to make the wear gap
below the axle, which is where it is when actually rolling something.
In other words, any adjustment made without pressure being applied by
the bearings will ignore any wear that has developed.
The correct way is to take a bit of copper sheet, about 3mm wide,
and roll 20-30mm of one end at the left-hand end of the rolls, then
reverse the direction to take it out and then roll the other end at
the right-hand end. You then carefully measure the thickness at each
end and adjust the rollers accordingly.
I usually take a longish strip of copper, bend it into a long "U"
shape so that the two ends are at either end of the rollers, and
roll both ends at the same time. I then measure with a micrometer and
adjust as required.
Regards, Gary Wooding