Helical gear design Helical gear design tterb83 (Mechanical) (OP) 16 Mar 16 20:11 I am working on designing a gearbox I am trying to determine what the optimal helix angle I need is and what the optimal face length should be. besides noise reduction what advantage/disadvantage is there with increasing the helix angle? between say 15deg-20deg. is there an optimal face length depending on what helix angle I have? Brett RE: Helical gear design MikeHalloran (Mechanical) 17 Mar 16 01:44 I think the tooth face has to be long enough and angled sufficiently that one end of a given tooth is leaving contact just as the surface at the other end of the next tooth is coming into contact. ... but you really should consult your Dudley Gear Handbook, which you really should have on your desk if you're designing gears. Mike Halloran Pembroke Pines, FL, USA RE: Helical gear design 3DDave (Aerospace) 17 Mar 16 02:20 This is one of those questions that costs between $1000 and $50,000 to answer, depending on the size of the drive required. You'll either spend it on gear design books, gear design experts, or pulverized failed attempts. Best bet is to buy a gearbox that carries the torque and horsepower required; the factors you mention will have been considered already. RE: Helical gear design tbuelna (Aerospace) 18 Mar 16 02:42 Quote (tterb83)is there an optimal face length depending on what helix angle I have? If noise or dynamic loading (transmission errors) are a concern, for a given helical gear face width you should adjust the helix angle to obtain a suitable face contact ratio, usually >2.0. The face width should be sufficient to meet requirements for tooth bending and contact fatigue stress, as well as providing adequate scoring margin. RE: Helical gear design gruntguru (Mechanical) 21 Mar 16 03:03 The main disadvantage is increased thrust load as helix angle increases. je suis charlie RE: Helical gear design tbuelna (Aerospace) 22 Mar 16 01:42 gruntguru- You make a good point. Gear design is always an exercise in compromise. One way to achieve a suitable face contact ratio with a single helical gear mesh, while also minimizing axial mesh forces, would be to use the widest practical face width and minimum helix angle. As a general rule, the L/D ratio of a single helical spur gear should be kept below 1.6.