stupid question?

[bob99]

Excuse the stupidity, but whats the point of having a straight cut gearbox?

 

I know nothing about them, apart from they seem to make a lot more noise than a standard box.

[murph7355]

I think transmission losses are less than on a "normal" box and that in skilled hands the changes can be made quicker.

 

I'd also think that the internals are simpler which could result in some weight saving/better reliability/cost benefits, but possibly not all of these or very much of any...

[murph7355]

Double post. Doh!

 

Edited by - Andy Murphy on 4 Jan 2001 21:21:26

[Powderpuff]

Don't straight cut boxes have an adverse effect on your hearing question.gif wink.gif

[CHRIS CLARK]

PARDON ?

[Fast Westie]

Bob

Main reasons for a straight cut gearbox:

- Gear teeth can be made bigger for width of gear hence stronger

- Less losses than helical cut gears i.e. more power and less heat

- Less side loads on gears and bearings

- Makes the car sound like a proper racing car smile.gif

[EFA]

Errr its also much much cheaper (easier) to tool up to cut straight cut gears as opposed to helical. This means many more ratios are available.

 

The helical boxes (except the Caterham 6 speed) have gear ratio's designed for 75bhp family saloons to pull caravans. Not really appropriate for a Caterham eh...?

 

 

AW

 

Arnie Webb

Organiser- L7C Le Mans Trip

[V7 SLR]

Having heard several conversations on this topic, I would have thought there were less genuine reasons than ever nowadays to support the use of a straight cut box over a helical one. For example, it has been said the transmission losses associated with the sideways-to-line-of-rotation forces are minimal when compared to the power output of your engine and weight of your car. I read somewhere (Se7ens list..?) of someone who'd tried similar/same gear ratios in both helical and straight cut derivatives. The difference in HP measured on a rolling road between the two wasn't measurable.

 

Then there's the strength issue. All modern metals should be up to the job. If you replace a type-9 box's gearing with new Quaife gears then of course it'll be stronger. The Quaife gears have only been designed recently, out of the latest metals, whereas the type-9 gears were designed 100 years ago and were manufactured out of wood (compared to the quality of Quaife's metal anyway). Strength would appear to have less to do with the type of cut and more to do with the metal quality. I got this from the Quaife man at the Autosport show 2 years ago. They sell helical gearsets too. And I suppose you could cite Caterham's BGH-designed 6-speed box as a good example of helical gearing being up to the job too... OK, the original ones had a few failures but I don't believe this was with stripped teeth. Admittedly, a straight cut should be stronger if you use the same materials and thickness of cog wheel, but materials being what they are these days, every

 

As for bearing wear associated with side loads, well again, it's down to modern materials etc...

 

In theory the only advantage of a straight cut gearset over a helical one must be the cost. It's easier to cut straight teeth, and if engineered correctly you should be able to make your cogs slightly thinner, saving you metal/cost.