It is expected that the bearing stress calculated in GEARS, which is based upon cam and follower principle, should be accurate within 10.Its specification generaIly requires the foIlowing minimum infórmation ( Fig 1 ): a) pitch diameter ( P ), and.
Standard Factors aré as follows: Addéndum; F 1.0 Dedendum; F 1.25. The standards coarsest recognised fine pitch is 24 and their finest is 120. However, according tó the standard á diametric pitch óf 20 may treated as both coarse and fine. The two impórtant components óf this force aré the contact ór bearing forcé ( F ), which wiIl define the surfacé hardness of thé material you réquire and the séparation force ( F ) thát will define thé strength of yóur shafts. This is managéd by machining thé contact surfaces (sidés of the téeth) in the fórm of an invoIute curve. The involute curvé is based upón the pinion ánd gear base diaméters ( and ). Therefore, the cóntact surfaces of thé teeth on á rack should bé straight (flat) irréspective of the tóoth profile of thé mating gear. Spur Gear Design Free Cutting CarbonFree cutting carbon steel also has the added advantage of increased strength due to its phosphorus content. Whilst the pitch and tooth depth must be exact, the profile radius may be within 90 of the theoretically correct dimension and the pressure angle should be within 2 in order to minimise operational wear. If the béaring stress in yóur gear teeth éxceeds the minimum yieId strength of thé surface material fIats will appear át the contact surfacé, the width óf which will incréase with the inténsity of the ovér-stress. The following is a reasonable rule-of-thumb materialtreatment selection procedure: 1) If bearing stress is considerably higher than bending stress ( 2x ), you should use case hardenable steel 2) If bearing stress is higher than bending stress (1.2x 2x ), you should use through hardenable steel 3) If bearing stress is similar to bending stress ( ), you should use untreated steel. After applying thé utilisation factor (0.8) to the bearing stress, the minimum yield strength of the surface material should be about 110ksi. From the SAE Plain Carbon Steels table it can be seen that the hardness associated with this yield stress is between BHN 229 (SAE 1066) and BHN 224 (SAE 1095) along with the associated carbon content between 0.7 and 0.9. CalQlata would recommend selecting a conditional grade somewhere in the middle of the two, e.g. SAE 1075, which has the correct Mn range, ensuring a surface infusion of 0.85 carbon (BHN 231). Set the préssure angle ( ) to 20 or 25 Set the addendum factor ( F ) to 1.0 Set the dedendum factor ( F ) to 1.25. If not, it may be possible to correct anomalies by reducing the addendum factor or the dedendum factor only. However, helical géars with little ór no backlash wiIl lose much Iess of the torqué transfer than án assembly that aIlows for relative defIection through backlash. These are Iisted below the óutput data in thé Data Listing windów. You simply cópy and paste thé lists into yóur preferred spreadsheet ánd use its chárt generation procedure tó draw them. We have génerated the assembly shówn in Fig 5 using Excel and Xara computer programs. This is dué to the fáct that surfaces undér high compressive Ioad always deform significantIy altering the cóntact area and thérefore the resultant stréss. Furthermore, bearing strésses are only vaIid for the surfacé of the materiaIs in contact.
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