We put _iron backs_ on our under-runners, to protect the stone from wearing out of balance.
Millers as a rule know that a stone in standing balance is not always in running balance, and _vice versa_, yet they are well aware that a stone should be in both. The reason these two balances do not always exist at the same time, or why the _light_ side of a stone standing should seem the _heavy_ side on running, is not clearly understood, and hence the difficulty in obviating the trouble. The importance of a correct standing balance and at the same time a true running balance, cannot well be over-estimated. Suppose the balancing weights in a runner are so adjusted that the stone stands in balance on the cock-head when raised above the bed-stone, but on starting, instead of its face remaining true and running steady, one side droops, and it runs with an apparent vibration or oscillation of the face. It will be found, however, upon examination, that it will always run with the same side low--going to show that the difficulty is centered in one certain point.
In these cuts are shown the improved balance boxes adopted by us. The one on the right is the box complete. They are placed in the runner with the rounding part in contact with the band, with the lid of the box a little below the plaster back. The figure to the left illustrates the inner adjustable box and screw for adjusting the same when in the stone. It will be noticed it has two parts divided by a partition. The cover to this inner box shown in the middle figure is secured with a screw, and fits down upon the box and close over the division, so that either side may be used when the weight is wanted at a point between any two of the balance boxes. We put five of them in a runner stone. This number is deemed entirely sufficient. They are made of cast-iron and fit up in good style, the wrought screws being all tapped into the iron. We find this balance box gives the miller entire control of the runner, and easy to operate, simply by removing the curb and letting the stone rest in position. A wrench is all the tool needed; the weights when in position are not subject to derangement, as those ordinarily used.
Now that we have the means explained by which this important work is to be done, next comes the question, How shall I do it? First, we would say, put the runner in standing balance in the usual manner, and lowering the required weight to the bottom of the boxes. In mills with the old style of stiff driving irons the spindle and driver must be _carefully_ trammed to the runner, as well as a proper bearing and a good fit of the cock-head into the cockeye; unless this is attended to it will be no use to proceed. Where our self-tramming driving irons are used, the process of putting in a balance will be a pleasure instead of a long disagreeable process, and it will be more perfect than is possible with any other appliance for this purpose.