Board logo

Advantages of a straight cut box ??
wacomuk - 6/2/07 at 07:03 PM

What are the advantages of a straight cut box over a semi helical box ?

faster gear change?
handle more power?

DIY Si - 6/2/07 at 07:05 PM

Handles more power. Faster changes may happen too, but if so it's due to uprated synchro bits rather than the straight cut gears. A dog box will give a faster change though, but that's normally a whole new level of expensive!
Oh, they also sound brilliant!

[Edited on 6/2/07 by DIY Si]

kikiturbo - 6/2/07 at 07:09 PM

straight cut box has less frictional losses... and, you have no axial thrust when using straight cut gears... also, as far as I am aware, straight cut gears are a bit stronger..

now, shifting is a matter of using synchro mesh or dog angagement with no synchro rigns... but that has nothing to do with helical or non helical gears, you can have a non synchro box with helical gears...

straight cut boxes have some free movement between gears and are much more noisy...

nasty-bob - 6/2/07 at 07:15 PM

I've always found this one a bit strange because as I understand it, helical gears are inherintly stronger as the load is spread over 2 teeth as opposed to one with straight cut.

Straight cut gears don't however produce the axial load that helicals do so maybe thats why they are seen as more robust.

Also, I would imagine replacement straight cut gears are made from better materials than the standard mass produced helical ones.

DIY Si - 6/2/07 at 07:18 PM

It is normally spread over 2 or more teeth, but only part of them so the difference in contact area is minimal. The teeth on straight cut gears tend to be thicker and made of better materials, so are stronger. Ie 1 big tooth is better than 2 halves of weaker ones.

jack trolley - 6/2/07 at 07:28 PM

They sound bloody awful - an incessant whine

John Bonnett - 6/2/07 at 07:33 PM

I agree, they do sound awful. I am running a Trannex straight cut box and on the road it's a real pain but it does handle the power and on the circuit a bit of a whine is no problem.

britishtrident - 6/2/07 at 07:40 PM

Real reason is down to manufacturing it is much easier to cut straight cut gears.

greggors84 - 6/2/07 at 10:04 PM

I agree with Calvin! They sound delightful!

quote:
Originally posted by jack trolley
They sound bloody awful - an incessant whine

greggors84 - 6/2/07 at 10:05 PM

So racing cars use straight cut gears because they are easier to manufacture?

quote:
Originally posted by britishtrident
Real reason is down to manufacturing it is much easier to cut straight cut gears.

givemethebighammer - 6/2/07 at 11:09 PM

quote:
Originally posted by greggors84
I agree with Calvin! They sound delightful!

quote:
Originally posted by jack trolley
They sound bloody awful - an incessant whine


Thirded, I love the sound of my TranX box (the ratios are great too)

nick baker - 12/2/07 at 11:18 AM

quote:
Originally posted by givemethebighammer
quote:
Originally posted by greggors84
I agree with Calvin! They sound delightful!

quote:
Originally posted by jack trolley
They sound bloody awful - an incessant whine


Thirded, I love the sound of my TranX box (the ratios are great too)



I agree too.. As an ex mini-nut ..(well, scamps really) there's nothing like the whine of as traigh cut box and the wail of a stressed A-serised engine to make me smile...

The tooling and Methods of manufacturing gears either helical or straight are usually very similar. The only difference is that the helical gears need to be rotated while being cut.

The main reason Helicals are used in production machinery is the reduced back-lash and and constant mesh of the teeth, hence reduced noise.

The teeth slide against each other in more places with a helical cut: this reduces the efficiency of the power-transfer.

As has been pointed out before, Axial thrust is a big issue with helical cuts leading to the use of large thrust bearings.

Straight-cuts transfer power with more efficiency, and at the "cost" of higher noise.

Personally I'd pay more for the privaledge of a straight-cut 'box. That noise is the best soundtrack to drive with....

britishtrident - 13/2/07 at 07:42 AM

quote:
Originally posted by greggors84
So racing cars use straight cut gears because they are easier to manufacture?

quote:
Originally posted by britishtrident
Real reason is down to manufacturing it is much easier to cut straight cut gears.


It was the only option in the old days because companies like Hewland and Jack Knight started out as garden shed operations, and the Machine tool needed for hobbing a straight cut gear is much simpler ad cheaper. Also back in the early days of Formula Ford the cost of gear sets was very important.