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Mini Spares Evo Helical Heavy Duty Gearset


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#16 Java_Green

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Posted 10 January 2024 - 08:37 PM




I have also considered using the mini spares heavy duty helical gearset. However, my main concern is about the gearbox housing when putting a lot of torque through the gearbox. Straight cut gears do not produce force transfer losses ending up as axial loads and in forth gear it should be fairly quiet as the load goes straight through the mainshaft. Worst case, using helical gears, should be in second gear during "drive" (opposite to "coast") where the layshaft is pushed towards the centre web of the gearbox housing. (At this very moment I do not have a gearbox at hand to measure the different gear radius to calculate the actual axial force level based on typical torque figures) I guess second gear is a gear that is most likely to be used when using full engine torque...

Just me thinking....

Not sure for others, but I rarely use full throttle in second. Mainly 3rd and 4th. I love the maths to this, a few people at work have crunched the numbers and it isn't as bad as i first thought. My other consideration of straight cut was the numerous gearboxes that have had the centre web split due to the gears trying to climb over each other at high torque loads. The evo helical sets are in a lot of high powered turbo A series engine set ups now. I know of at least 2 now running over 250lbft for a few years now. Time will tell on the cases, and bearings, as to the longevity!
250lbft is a lot to put through a mini gearbox.... You mentioned a reason for the centre web cracking. Is it true that it is due to using straight cut gears? I cannot see why the evolution heavy duty gearset would spare the centre web, somebody who can explain? I cannot really see why. Is it still true using a pinion support?
It's due to the opposing forces on the shafts - If leverage is the same, then load can't be added from elsewhere. In that manner helical transfers some of the load through another axis. Force = Blue + Red

HelicalGearsThrust.jpg

Imagine this as straight cut, all the forces will all be in the blue direction, therefore Force = Blue

Ive not seen a web split on a helical set yet, however that's not to say it isn't possible.

I do understand what you mean with the forces pushing the shafts apart. Still, I cannot see the purpose with using such a gear tooth profile (perhaps there could be a cost benefit...). A straight cut gear should have a gear tooth contact surface normal that is tangential to the gear. If so, I would say the forces separating the shafts would be very small and solely due to existing shaft bending. Is there someone who can share a close up photo of the crack surface? (I am interested to see, suspect the root cause for cracking could be that SC gears excitate a resonance mode of the centre web)

Helix cut gears are mainly stronger due to that they have a tooth engagement number larger than 1. (SC gears typically has 1)

#17 Java_Green

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Posted 10 January 2024 - 08:43 PM

Trouble with the forum posting several copies and could not delete....

Edited by Java_Green, 10 January 2024 - 08:56 PM.


#18 Java_Green

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Posted 10 January 2024 - 08:46 PM

.

Edited by Java_Green, 10 January 2024 - 08:53 PM.


#19 Steve220

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Posted 11 January 2024 - 05:17 PM

thats fine, but straight cut gear kits are measurably less lossy than a helical kit arn't they??

They are. But the gears themselves are weaker due to less cross section contacting.



#20 Steve220

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Posted 11 January 2024 - 05:20 PM

 

 

 

 

I have also considered using the mini spares heavy duty helical gearset. However, my main concern is about the gearbox housing when putting a lot of torque through the gearbox. Straight cut gears do not produce force transfer losses ending up as axial loads and in forth gear it should be fairly quiet as the load goes straight through the mainshaft. Worst case, using helical gears, should be in second gear during "drive" (opposite to "coast") where the layshaft is pushed towards the centre web of the gearbox housing. (At this very moment I do not have a gearbox at hand to measure the different gear radius to calculate the actual axial force level based on typical torque figures) I guess second gear is a gear that is most likely to be used when using full engine torque...

Just me thinking....

Not sure for others, but I rarely use full throttle in second. Mainly 3rd and 4th. I love the maths to this, a few people at work have crunched the numbers and it isn't as bad as i first thought. My other consideration of straight cut was the numerous gearboxes that have had the centre web split due to the gears trying to climb over each other at high torque loads. The evo helical sets are in a lot of high powered turbo A series engine set ups now. I know of at least 2 now running over 250lbft for a few years now. Time will tell on the cases, and bearings, as to the longevity!
250lbft is a lot to put through a mini gearbox.... You mentioned a reason for the centre web cracking. Is it true that it is due to using straight cut gears? I cannot see why the evolution heavy duty gearset would spare the centre web, somebody who can explain? I cannot really see why. Is it still true using a pinion support?
It's due to the opposing forces on the shafts - If leverage is the same, then load can't be added from elsewhere. In that manner helical transfers some of the load through another axis. Force = Blue + Red

HelicalGearsThrust.jpg

Imagine this as straight cut, all the forces will all be in the blue direction, therefore Force = Blue

Ive not seen a web split on a helical set yet, however that's not to say it isn't possible.

I do understand what you mean with the forces pushing the shafts apart. Still, I cannot see the purpose with using such a gear tooth profile (perhaps there could be a cost benefit...). A straight cut gear should have a gear tooth contact surface normal that is tangential to the gear. If so, I would say the forces separating the shafts would be very small and solely due to existing shaft bending. Is there someone who can share a close up photo of the crack surface? (I am interested to see, suspect the root cause for cracking could be that SC gears excitate a resonance mode of the centre web)

Helix cut gears are mainly stronger due to that they have a tooth engagement number larger than 1. (SC gears typically has 1)

 

It is merely down to how the load is distributed. Straight cut gears try and ride over each other as that's where the forces are. Helical in OEM vehicles is done for noise primarily. It's the no.1 reason i went helical over straight cut.



#21 Java_Green

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Posted 11 January 2024 - 08:49 PM

The noise is definitely a big factor when considering helical cut gears. I thought it would be barrable with SC gears since it is only 1st to 3rd.
My main concern is actually not the gearbox but instead the transfer gears which I certainly do not want to have straight cut. How do you (Steve220) and your "torque brothers" handle this?

#22 Gaz66

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Posted 11 January 2024 - 09:54 PM

AHH, a good old straight Cut Vs helical posting.
Can't beat it 😁

#23 Steve220

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Posted 12 January 2024 - 07:03 PM

The noise is definitely a big factor when considering helical cut gears. I thought it would be barrable with SC gears since it is only 1st to 3rd.
My main concern is actually not the gearbox but instead the transfer gears which I certainly do not want to have straight cut. How do you (Steve220) and your "torque brothers" handle this?


Most go straight cut, but I went for oil fed thrusts! If you check out my build thread, there's images of it.

#24 Java_Green

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Posted 14 January 2024 - 07:10 AM

The noise is definitely a big factor when considering helical cut gears. I thought it would be barrable with SC gears since it is only 1st to 3rd.
My main concern is actually not the gearbox but instead the transfer gears which I certainly do not want to have straight cut. How do you (Steve220) and your "torque brothers" handle this?

Most go straight cut, but I went for oil fed thrusts! If you check out my build thread, there's images of it.

Hmmm... And Paul made your oil fed modifications... Unfortunately, he is far from where I live...

#25 Steve220

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Posted 14 January 2024 - 08:58 AM

Same here. I shipped all the parts to him (gearbox and transfer case) and he did the work. My last version of the drops chewed the casings when the shims grabbed the idler, needed some improvement for longevity and power!




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