A Supplementary note on the Mould board described in a letter to Sr. John Sinclair of Mar. 23. 1798. inserted in the American Philosophical transactions Vol. 4. and in Maese’s Domestic Encyclopaedia voce Plough.
The chief object in that description was to establish the true principle on which the mouldboard of a plough should be constructed, and to point out a mechanical method of making it’s curved surfaces. the mould board there described, by way of example, was made with a square toe, to recieve the sod at the hinder edge of the fin of the plough-share. but neither the principle nor the method is restrained to that single form. if it be desired for instance to give to the mouldboard a pointed toe, adapted to the fin of the plough-share, which may begin to raise the sod from the point, a small variation in the process effects it, and the principle of the curved surface is still the same. Having formed your block of the length, breadth & height, suited to the nature of your soil, to the breadth & depth of your furrow, having scribed it, & taken out the pyramidal block as directed, lay it bottom upwards and draw [GRAPHIC IN MANUSCRIPT] a line a.b. across it, distant from the fore end about once & a half the breadth of the bottom. then draw the diagonal a.c. and if you wish to make the toe with the cutting edge oblique & straight chip off the corner d. to the diagonal line a.f.c. or if you wish to make the cutting edge curved as that of the fin generally is, lay off the curvature you desire from f. to e. and either mark the curve by the eye, or with a pair of compasses, & chip off the corner d. to the curved line a.e.c. then saw in on your scribes & finish as directed in the letter. it is hardly necessary to observe that the block being here represented bottom upwards, the cutting edge of the mould board appears on the left, tho’ it will really be on the right when turned up.
DLC: Papers of Thomas Jefferson.