Straight cut gears?

"BaconSandwich is tasty." (baconsandwich) 11/13/2015 at 22:57 • Filed to: None

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I’m curious - is there any advantage to straight cut gears vs. a more traditional cut gear? I mean, other advantages, other than the wonderful noise they make.

aberson Bresident of the FullyAssed Committe > BaconSandwich is tasty. 11/13/2015 at 23:02

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They’re stronger

and less chance of them popping out in high stress situations ( i think.)

bob and john > BaconSandwich is tasty. 11/13/2015 at 23:07

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that “wonderful’ noise gets really fucking annoying real quick.

like aperson said. stronger and less stress on the gear box, as the gears arent pushing themselves sideways under power

BaconSandwich is tasty. > aberson Bresident of the FullyAssed Committe 11/13/2015 at 23:12

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Makes sense. I did come across something that essentially said there are less stresses trying to push the gears apart.

BaconSandwich is tasty. > bob and john 11/13/2015 at 23:14

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I do think they have some interesting applications in electric motorcycles, though. It gives a bike a bit of futuristic noise. The Harley Davidson Live Wire seems like it uses some sort of straight cut bevel gear:

bob and john > BaconSandwich is tasty. 11/13/2015 at 23:14

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all motorcycles are straight cut gears to begin with. that just the sound of the electric motor.

Distraxi's idea of perfection is a Jagroen > BaconSandwich is tasty. 11/13/2015 at 23:15

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Straight cut gears (which are the “traditional” one - helical is a newfangled invention from the late 1800s) offer more strength for a given gear width and tooth size, due to the tooth engaging across the full width (depending on the design, helicals often only have partial engagement at any instant), and because 100% of the contact force is in the direction of drive - with helicals there’s also a sideways component, which means a greater load on the contact area per unit torque.

They also run cooler, because there is less sliding contact than with a helical.

Plus they can be manufactured faster and on cheaper equipment.

Against that, they have more uneven force transmission as succeeding teeth engage and disengage, which leads to noise and vibration, and possibly less durability than helicals (depending on whether fatigue or heat is the dominant ageing factor in the installation in question).

BaconSandwich is tasty. > Distraxi's idea of perfection is a Jagroen 11/13/2015 at 23:19

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Excellent answer. It makes me wonder - would shaping the teeth a little differently would help cut down on the noise.

Distraxi's idea of perfection is a Jagroen > BaconSandwich is tasty. 11/13/2015 at 23:25

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Possibly, but there would be negative effects which would presumably be larger than those of cutting the gears at an angle - a lot of smart people have spent a lot of time on gear noise, and helical is what everyone uses.

The standard gear profile is called an “ involute curve ”, and it’s designed to ensure the force transmission remains at a constant angle throughout the engagement, giving even torque transmission while avoiding any sliding contact of the teeth. It’s actually pretty ingenious. And what makes it even better is it can be drawn by wrapping a piece of string round a circular blank and attaching a pencil to it, which made it feasible for your 18th century carpenter or blacksmith to manufacture.

BaconSandwich is tasty. > Distraxi's idea of perfection is a Jagroen 11/13/2015 at 23:59

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That is incredibly neat!

I Will Always Be The Honey Badger > BaconSandwich is tasty. 11/14/2015 at 00:59

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I love planetary gears. So mesmerizing to watch them go around.

Drakkon- Most Glorious and Upright Person of Genius > BaconSandwich is tasty. 11/14/2015 at 08:54

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Straight cut gears make that ear splitting noise you call wonderful.

Straights are also stronger and usually used in sequential boxes because you can only go 1-2-3-4-3-2

Helical cut gears are not as strong, they are much quieter and they are easier to shift. The curve allows them to ‘take up’ smoother and with less effort. Because of this (plus synchro cones) they are easily shifter in any order. You don’t have to be a rev-matching guru to drive them well.