Baltimore 24 of the 6 mo 1808.
My dear Friend,
A few days since, I returned from the Eastward, where I had been viewing and examining in operation the various machinery for manufacturing cotton. Thy favor of the 12 ultimo came to Brookeville during my absence, and remained there until my return. This will account for my not sooner attending to thy request. I am so far from feeling it a trouble, that to have the power and opportunity of executing any of thy commands, is to me always a high gratification.
I have visited the Oil-mill mentioned by General Dearborne. On the shaft of the water-wheel is a Spur-cog-wheel; on the top of this wheel, and driven by it, is a smaller spur, the shaft of which lies horizontally. In this shaft, about its middle, are inserted cams to lift two drivers—one to drive the pressing wedge, the other to drive the inverted or releasing wedge. On the end of this shaft farthest from the water wheel is a wallower which drives a face-cog-wheel on the upper end of the perpendicular shaft which governs two vertical stones in the manner of a Tanner’s bark mill. These stones grind the seed, on what is called a Bed-stone, they being called Runners; all of the thickness of common millstones. The bedstone is 4½ feet diameter—the runners 5 feet 10 inches; these run upon an iron axle (passing through the perpendicular shaft) 3 inches square, and 20 inches long, between the shoulders. The curbing round the bedstone is 7 feet diameter, surrounded by a hoop 9 inches high. There are two sweeps or tenders to keep the seed under the runners. The proper velocity for the perpendicular shaft is 10 revolutions in a minute.
The Press is a piece of timber 2 feet square and 8 feet long, with a mortice in it, 2½ feet long, 9 inches wide at top, 8½ at bottom, and 18 inches deep, lined at each end with strong sheet iron which should come about 7 or 8 inches along each side to prevent its leaking.
The forcing wedge is 18 inches long and tapers 3 inches, the length and taper of the releasing wedge is the same. The Drivers are hickory, 14 feet long, 6 inches by 9, and are lifted 2½ feet above the forcing wedge when driven home. [GRAPHIC IN MANUSCRIPT]
I have supposed it unnecessary to give any description of the contrivance for warming the meal before pressing in order that it may yield a greater quantity of oil, as I take it for granted that oil for the Table ought always to be cold-drawn.
I will now describe a mill and press, in my judgment, every way better adapted to thy purpose than the preceding—more neat, more compact, more powerful, and less expensive.
The mill is now in use for grinding flax-seed at Ellicott’s near Baltimore, and consists simply of two equal, cylindrical, cast-iron Rollers, running in contact or nearly so—their axes placed in the same horizontal plane. The seed is received between them above and is discharged below. These rollers are 15 inches long, and 6 inches diameter. A pinion of 12 leaves on one roller is connected with a pinion of 11 leaves on the other. The pitch-circle, of the larger pinion is 6.26 inches diameter, and that of the smaller 5.74 inches. The sum of the diameters of the pitch-circles must be equal to the sum of the diameters of the rollers. This difference of velocities in the rollers produces the effect of rubbing or grinding what is between them, of making the rollers themselves perfectly true if they were not so at first, and of continuing them so forever. They should make about 100 revolutions in a minute.
The Hydrostatic Press (a description of which is in the british repertory of arts, and a model of the same in the U.S. patent office) is in my opinion far preferable to any other press I have ever seen—where it is desirable to have neatness of construction, great power, and facility of application, in a small compass. I have seen this press in operation in New Orleans, packing cotton for exportation.
Wilt thou be able to preserve our beloved country in Peace, externally and internally? I am persuaded it is the honest wish of thy heart. Accept my salutation of affectionate esteem and respect.
DLC: Papers of Thomas Jefferson.