. Machine design. rectangular, hollow andI shaped sections were tested until a maximum wasreached in the I section with heavy tension flangewhich broke under a load of 38,000 lb. Channel andT shaped sections such as are appropriate for fly-wheelrims were also tested with the ribs in tension and incompression. The strength of such sections was- found to be fromtwo to three times as great when the ribs were in com-pression as when they were in tension. Resistance to Twisting. Thehollow circular section is the idealform for all frames or machinemembers which are subjected totorsion. If subjected
. Machine design. rectangular, hollow andI shaped sections were tested until a maximum wasreached in the I section with heavy tension flangewhich broke under a load of 38,000 lb. Channel andT shaped sections such as are appropriate for fly-wheelrims were also tested with the ribs in tension and incompression. The strength of such sections was- found to be fromtwo to three times as great when the ribs were in com-pression as when they were in tension. Resistance to Twisting. Thehollow circular section is the idealform for all frames or machinemembers which are subjected totorsion. If subjected also tobending the section may be madeelliptical or, as is more common,thickened on two sides by makingthe core oval. See Fig. 6. AsFig. 6. has already been pointed out the box sections are in general betteradapted to resist twisting than the ribbed or I sec-tions. Frames of Machine Tools. The beds of lathes aresubjected to bending on account of their own weightand that of the saddle and on account of the downward. MACHINE FRAMES. 23 pressure on the tool when work is being turned. Theyare usually subjected to torsion on account of the un-even pressure of the supports. The box section is thenthe best; the double / commonly used is very weakagainst twisting. The same principle would apply indesigning the beds of planers but the usual method ofdriving the table by means of a gear and rack preventsthe use of the box section. The uprights of planersand the cross rail are subjected to severe bendingmoments and should have profiles of uniform uprights are also subject to side bending when thetool is taking a heavy side cut near the top. To pro-vide for this the uprights may be of a box section ormay be reinforced by outside ribs. The upright of a drill press or vertical shaper isexposed to a constant bending moment equal to theupward pressure on thecutter multiplied by thedistance from center ofcutter to center of up-right. It should then beof constant cross-sectionfrom t
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Keywords: ., bookcentury1900, bookdecade1900, bookpublishernewyo, bookyear1906
