13 replies to this topic

[mic]

Heard of em but dont really know the difference in one o them and a standard 'box!

is the one with s/c the 'loud' one? (i want one if it is )

mic

[Guess-Works.com]

In a standard box, the 2nd 3rd and 4th (technically not a gear at all) are helical cut, meaning the gears are ground on an angle or helix. Straight cut gears are cut parallel to the centre of rotation, 1st is straight cut in all mini boxes...

[Bungle]

is there a reason 1st is straight cut ?

[Big_Adam]

Right,

S/C or Straight Cut as it is know is a way the gears are cut. On a standard gearbox their cut at a weird angel. Straight cut are cut like regular cogs and wheels with straight teeth. Developed/used in mini's for rally as the drivers just kept their foot planted to the floor so with a regular gear box they spun bearings out. Straight cut was used to solve this problem. As well as straight cut loose less energy in the drive train. So more power to the wheels.

Their "loud" beacuse of teeth chatter (anther reason the angel cuts ones are uses, quietness).

Good Mr Guessworks is the gearbox man and does build straight cut boxes if you are interested but they normally cost around £1000 +

edit

damnit. waffled on too long!

Edited by Big_Adam, 23 March 2007 - 06:14 PM.

[Guess-Works.com]

is there a reason 1st is straight cut ?

Yes....

[Guess-Works.com]

Spose you want to know why aswell

[The Matt]

Spose you want to know why aswell

Teaser!

[Guess-Works.com]

Well...

The reason the 1st gear is Straight cut, is the reverse gear...

basically, reverse is provided by what's called the reverse idler, this is a crash gear which slides across when selected, and locks into the 1st gear on the laygear and the geared ring of the 1st/2nd synchromesh... This arrangement is fairly unique to the mini gearbox (and spridget gearbox which you may no know shares a lot of components with the mini box), most other gearboxes have a dedicated gear ground on the laygear for reverse

If 1st gear were helical cut it would be near impossible to get reverse gear to engage...

Edited by GuessWorks, 23 March 2007 - 06:38 PM.

[Guess-Works.com]

I think I also out spammed bungle 4 to 1 then

[Bungle]

can i now have that expiation in idiot form ?

[The Matt]

the teeth are straight so that the reverse idler can slide in easier from the side

[Dan]

Straight cut boxes pretty much only exist now because it is much easier and cheaper to produce the gears and easier to change the ratios. This is really why racers use them as they will tend to change ratios often (sometimes for different circuits) and buy new gears regularly. They are weaker than helical cut gearboxes and consume slightly less power but not much. Helical gears put more side loading on the thrust bearings but that is easily dealt with especially as racers re-build or inspect so often. It is an old fashioned design really.

[fikus01]

old design maybe but stil used to this day in race cars and high torque producing engines alike!, especially commercial lumps!

[mini93]

to stop side loading come comersials use double helicle cuts basicly "v"-ing towards each other