Three models, as shown in Fig. 1, were exhibited; all were of the same general dimensions and containing the same amount of material.  The one made on the box principle, c, proved to be fifty per cent. stiffer in a vertical direction than either a or b, from twenty to fifty times stiffer sidewise, and thirteen times more rigid against torsion than either of the others.

However strong a frame may be, its own weight and the weight of the work upon it tends to spring it unless evenly distributed, and to twist it unless evenly proportioned.  For all small machines the single post obviates all trouble, but for machine tools of from twice to a half dozen times their own length the single post is not available.  Four legs are used for machines up to ten feet or so, and above that legs various and then solid masonry.  If the four legs were always set upon solid masonry, and leveled perfectly when set, no question could be raised against the usual arrangement, unless it be this:  Ought they not to be set nearly one-fourth the way from the end of the bed? or to put it in another form:  Will not the bed of an iron planing machine twelve feet in length be equally as well supported by four legs if each pair is set three feet from the ends—­that is, six feet apart—­as by six legs, two pairs at the ends and one in the center, and the pairs six feet apart? there being six feet of unsupported bed in either case, with this advantage in favor of the four over the six, settling of the foundation would not bend the bed.

It is not likely that one-half of the four-legged machine tools used in this country are resting upon stable foundations, nor that they ever will be; and while this is a fact, it must also remain a fact that they should be built so as to do their best on an unstable one.  Any one of the thousand iron planing machines of the country, if put in good condition and set upon the ordinary wood floors, may be made to plane work winding in either direction by shifting a moving load of a few hundred pounds on the floor from one corner of the machine to the other, and the ways of the ordinary turning lathe may be more easily distorted still.  Machine tool builders do not believe this, simply because they have not tried it.  That is, I suppose this must be so, for the proof is so positive, and the remedy so simple, that it does not seem possible they can know the fact and overlook it.  The remedy in the case of the planer is to rest the structure on the two housings at the rear end and on a pair of legs about one-fourth of the way back from the front, pivoted to the bed on a single bolt as near the top as possible.

[Illustration:  a, b, c, Fig. 1, illustrate the models shown by Mr. Sweet, which represented three forms of lathe and planer construction.  The box form, c, proved to be fifty per cent. stronger in its vertical direction than either a or b, fifty times stronger sideways than a and twenty times stronger than b, and more than thirteen times stronger than either when subject to torsional strain.