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The cost of power for turning an engine on a flat disk is very small. Referring to Table 1, the cost for turning any of the engines did not exceed one-eighth of a cent with power at 3 cents a kw.-hr. Really, the power cost is a very small item for the usual center, disk or roller. Hence, a center which is low in first cost and maintenance, is the most desirable. A simple flat disk meets the requirements.

Now, how about turning by hand? If the table is at a point where only a few turns a day are made, a roller center is desirable for hand power. Although, a well-worn and lubricated disk center will answer as well. A new disk center would not receive enough wear to make it smooth. But wherever a tractor is used, I see no economy in a roller center. If there is a failure of power, the resistances are too great for hand operation, if the tractor is allowed to remain attached to the table.

The experiments show very clearly the relative great loss in the tractor. It is easily seen why it is difficult to turn, by hand, a table with the tractor attached.

A short time ago, I made an examination of a flat disk center which had been in service, for three years, at a point where about 100 engines a day were turned. The disk was very smooth; there was scarcely any

wear.

I have modified the design of the disk center. The thickness of the disk has been reduced to 27/2 inches. Other minor changes were made. The pedestal has been made lower. Recent bids for the modified design are as low as $400.00.

If any trouble arises in a properly designed flat disk center, it will be found due to a lack of a little common sense. This sense should be applied with the lubricant.

Why use a complex devise, like a roller center, when a simple disk is more economical?

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